Difference: GeneralTools (1 vs. 25)

Revision 252010-08-17 - SimonLeinen

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META TOPICPARENT name="WebHome"

Troubleshooting Procedures

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PERT Troubleshooting Procedures are laid down in this PDF, which also contains the User Guide for using the PERT Ticket System
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PERT Troubleshooting Procedures, as used in the earlier centralised PERT in GN2 (2004-2008), are laid down in GN2 Deliverable DS3.5.2 (see references section), which also contains the User Guide for using the (now-defunct) PERT Ticket System (PTS).
 

Standard tests

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  • PERT Troubleshooting Procedures - 2nd Edition, B. Belter, A. Harding, T. Rodwell, GN2 deliverable D3.5.2, August 2006 (PDF)
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-- SimonLeinen - 18 Sep 2005 - 20 Nov 2007
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-- SimonLeinen - 18 Sep 2005 - 17 Aug 2010
 -- BartoszBelter - 28 Mar 2006

META FILEATTACHMENT attachment="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" attr="h" comment="GÉANT2 Troubleshooting Procedures" date="1195222062" name="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" path="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" size="2033032" stream="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" user="Main.TobyRodwell" version="1"

Revision 242007-11-20 - SimonLeinen

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META TOPICPARENT name="WebHome"

Troubleshooting Procedures

PERT Troubleshooting Procedures are laid down in this PDF, which also contains the User Guide for using the PERT Ticket System
Line: 15 to 15
 

ip route show cache

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Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behavour can actually limit TCP performance - if the last transfer was poor, then the starting TCP paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
>
>
Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in response to what it learns from TCP (such parameters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behaviour can actually limit TCP performance - if the last transfer was poor, then the starting TCP parameters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
 
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-- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
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References

  • PERT Troubleshooting Procedures - 2nd Edition, B. Belter, A. Harding, T. Rodwell, GN2 deliverable D3.5.2, August 2006 (PDF)

-- SimonLeinen - 18 Sep 2005 - 20 Nov 2007

 -- BartoszBelter - 28 Mar 2006

META FILEATTACHMENT attachment="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" attr="h" comment="GÉANT2 Troubleshooting Procedures" date="1195222062" name="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" path="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" size="2033032" stream="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" user="Main.TobyRodwell" version="1"

Revision 232007-11-16 - TobyRodwell

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META TOPICPARENT name="WebHome"
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Troubleshooting Procedures

PERT Troubleshooting Procedures are laid down in this PDF, which also contains the User Guide for using the PERT Ticket System
 

Standard tests

  • Ping - simple RTT/loss measurement using ICMP ECHO requests
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 -- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
-- BartoszBelter - 28 Mar 2006
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META FILEATTACHMENT attachment="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" attr="h" comment="GÉANT2 Troubleshooting Procedures" date="1195222062" name="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" path="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" size="2033032" stream="GN2-06-094v6-Deliverable_DS3-5-2_PERT_Troubleshooting_Procedures-Second_Edition.pdf" user="Main.TobyRodwell" version="1"

Revision 222006-03-29 - SimonLeinen

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META TOPICPARENT name="WebHome"

Standard tests

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ping

Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies to determine the latency between those hosts. The output shows the Round Trip Time (RTT) between the host machine and the remote target. Ping is often used to determine whether a remote host is reachable. Unfortunately, it is quite common these days for ICMP traffic to be blocked by packet filters / firewalls, so a ping timing out does not necessarily mean that a host is unreachable.

(Another method for checking remote host availability is to telnet to a port that you know to be accessible; such as port 80 (HTTP) or 25 (SMTP). If the connection is still timing out, then the host is probably not reachable - often because of a filter/firewall silently blocking the traffic. When there is no service listening on that port, this usually results in a "Connection refused" message. If a connection is made to the remote host, then it can be ended by typing the escape character (usually 'CTRL ^ ]') then quit.)

The -f flag may be specified to send ping packets as fast as they come back, or 100 times per second - whichever is more frequent. As this option can be very hard on the network only a super-user (the root account on *NIX machines) is allowed to specified this flag in a ping command.

The -c flag specifies the number of Echo request messages sent to the remote host by ping. If this flag isn't used, then the ping continues to send echo request messages until the user types CTRL C. If the ping is cancelled after only a few messages have been sent, the RTT summary statistics that are displayed at the end of the ping output may not have finished being calculated and won't be completely accurate. To gain an accurate representation of the RTT, it is recommended to set a count of 100 pings. The MS Windows implementation of ping just sends 4 echo request messages by default.

Ping6 is the IPv6 implementation of the ping program. It works in the same way, but sends ICMPv6 Echo Request packets and waits for ICMPv6 Echo Reply packets to determine the RTT between two hosts. There are no discernable differences between the *NIX implementations and the MS Windows implementation.

fping

_fping_ is a ping like program which uses the Internet Control Message Protocol (ICMP) echo request to determine if a host is up. fping is different from ping in that you can specify any number of hosts on the command line, or specify a file containing the lists of hosts to ping. Instead of trying one host until it timeouts or replies, fping will send out a ping packet and move on to the next host in a round-robin fashion. If a host replies, it is noted and removed from the list of hosts to check. If a host does not respond within a certain time limit and/or retry limit it will be considered unreachable.

Unlike ping, fping is meant to be used in scripts and its output is easy to parse.

For more information please refer to http://www.fping.com.

Simple example of usage:


# fping -c 3 -s www.man.poznan.pl www.google.pl
www.man.poznan.pl : [0], 84 bytes, 1.44 ms (1.44 avg, 0% loss)
www.google.pl     : [0], 84 bytes, 126 ms (126 avg, 0% loss)
www.man.poznan.pl : [1], 84 bytes, 1.12 ms (1.28 avg, 0% loss)
www.google.pl     : [1], 84 bytes, 126 ms (126 avg, 0% loss)
www.man.poznan.pl : [2], 84 bytes, 2.18 ms (1.58 avg, 0% loss)
www.google.pl     : [2], 84 bytes, 126 ms (126 avg, 0% loss)

www.man.poznan.pl : xmt/rcv/%loss = 3/3/0%, min/avg/max = 1.12/1.58/2.18
www.google.pl     : xmt/rcv/%loss = 3/3/0%, min/avg/max = 126/126/126

       2 targets
       2 alive
       0 unreachable
       0 unknown addresses

       0 timeouts (waiting for response)
       6 ICMP Echos sent
       6 ICMP Echo Replies received
       0 other ICMP received

 1.12 ms (min round trip time)
 64.0 ms (avg round trip time)
 126 ms (max round trip time)
        2.548 sec (elapsed real time)

>
>
  • Ping - simple RTT/loss measurement using ICMP ECHO requests
  • Fping - ping variant with concurrent measurement of multiple destinations
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.
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  Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behavour can actually limit TCP performance - if the last transfer was poor, then the starting TCP paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
Deleted:
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-- TobyRodwell - 06 Apr 2005
-- OrlaMcGann - 26 Jul 2005 - 14 Jul 2005
 -- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
-- BartoszBelter - 28 Mar 2006

Revision 212006-03-28 - BartoszBelter

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META TOPICPARENT name="WebHome"

Standard tests

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  Ping6 is the IPv6 implementation of the ping program. It works in the same way, but sends ICMPv6 Echo Request packets and waits for ICMPv6 Echo Reply packets to determine the RTT between two hosts. There are no discernable differences between the *NIX implementations and the MS Windows implementation.
Added:
>
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fping

_fping_ is a ping like program which uses the Internet Control Message Protocol (ICMP) echo request to determine if a host is up. fping is different from ping in that you can specify any number of hosts on the command line, or specify a file containing the lists of hosts to ping. Instead of trying one host until it timeouts or replies, fping will send out a ping packet and move on to the next host in a round-robin fashion. If a host replies, it is noted and removed from the list of hosts to check. If a host does not respond within a certain time limit and/or retry limit it will be considered unreachable.

Unlike ping, fping is meant to be used in scripts and its output is easy to parse.

For more information please refer to http://www.fping.com.

Simple example of usage:


# fping -c 3 -s www.man.poznan.pl www.google.pl
www.man.poznan.pl : [0], 84 bytes, 1.44 ms (1.44 avg, 0% loss)
www.google.pl     : [0], 84 bytes, 126 ms (126 avg, 0% loss)
www.man.poznan.pl : [1], 84 bytes, 1.12 ms (1.28 avg, 0% loss)
www.google.pl     : [1], 84 bytes, 126 ms (126 avg, 0% loss)
www.man.poznan.pl : [2], 84 bytes, 2.18 ms (1.58 avg, 0% loss)
www.google.pl     : [2], 84 bytes, 126 ms (126 avg, 0% loss)

www.man.poznan.pl : xmt/rcv/%loss = 3/3/0%, min/avg/max = 1.12/1.58/2.18
www.google.pl     : xmt/rcv/%loss = 3/3/0%, min/avg/max = 126/126/126

       2 targets
       2 alive
       0 unreachable
       0 unknown addresses

       0 timeouts (waiting for response)
       6 ICMP Echos sent
       6 ICMP Echo Replies received
       0 other ICMP received

 1.12 ms (min round trip time)
 64.0 ms (avg round trip time)
 126 ms (max round trip time)
        2.548 sec (elapsed real time)

 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.
Line: 25 to 66
  -- TobyRodwell - 06 Apr 2005
-- OrlaMcGann - 26 Jul 2005 - 14 Jul 2005
Changed:
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-- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
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-- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
-- BartoszBelter - 28 Mar 2006
 

Revision 202006-02-26 - SimonLeinen

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META TOPICPARENT name="WebHome"

Standard tests

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  Ping6 is the IPv6 implementation of the ping program. It works in the same way, but sends ICMPv6 Echo Request packets and waits for ICMPv6 Echo Reply packets to determine the RTT between two hosts. There are no discernable differences between the *NIX implementations and the MS Windows implementation.
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traceroute

Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range. If there is no response to the probe within a certain time period (typically 5ms), then a * is displayed.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occasionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an ! will be printed beside the RTT in the output.

Other error messages that may appear after the RTT in the output of a traceroute are:

!H
Host unreachable
!N
Network unreachable
!P
Protocol unreachable
!S
Source-route failed (that is to say, the router was not able to honour the source-route option set in an IP packet)
!F[pmtu]
Fragmentation needed. [pmtu] displays the Path MTU Discovery value, typically the "next-hop MTU" contained in the ICMP response packet.
!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation
!C
Precedence cut-off in effect
![num]
displays the ICMP unreachable code, as defined in a variety of RFC, shown at http://www.iana.org/assignments/icmp-parameters

Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. Some *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the -I flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

Traceroute6 uses the Hop-Limit field of the IPv6 protocol to elicit an ICMPv6 Time Exceeded ICMPv6 message from each gateway ("hop") along the path to some host. Just as with traceroute, it prints the route to the given destination and the RTT to each gateway/router.
The following are a list of possible errors that may appear after the RTT for a gateway (especially for OSes that use the KAME IPv6 network stack, such as the BSDs):

!N
No route to host
!P
Administratively prohibited (i.e. Blocked by a firewall, but the firewall issues an ICMPv6 message to the originating host to inform them of this)
!S
Not a Neighbour
!A
Address unreachable
!
The hop-limit is <= 1 on a Port Unreachable ICMPv6 message. This means that the packet got to its destination, but that the reply only had a hop-limit large enough that was just large enough to allow it to get back to the source of the traceroute6. This option was more interesting in IPv4, where bugs in some implementations of the IP stack could be identified by this behaviour.

Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the -I flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter or firewall, while ICMP ECHO requests are permitted.

TCP Traceroute

TCPTraceroute is a traceroute implementation that uses TCP packets instead of UDP or ICMP packets to send its probes. TCPtraceroute can be used in situations where a firewall blocks ICMP and UDP traffic. It is based on the "half-open scanning" technique that is used by NMAP, sending a TCP with the SYN flag set and waiting for a SYN/ACK (which indicates that something is listening on this port for connections). When it receives a response, the tcptraceroute program sends a packet with a RST flag to close the connection.

There are a number of other Traceroute Like Tools available for diagnosing network problems.

 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.
Line: 60 to 23
  Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behavour can actually limit TCP performance - if the last transfer was poor, then the starting TCP paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
Changed:
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-- TobyRodwell - 06 Apr 2005 -- OrlaMcGann - 26 Jul 2005 -- OrlaMcGann - 14 Jul 2005 -- SimonLeinen - 18 Sep 2005
>
>
-- TobyRodwell - 06 Apr 2005
-- OrlaMcGann - 26 Jul 2005 - 14 Jul 2005
-- SimonLeinen - 18 Sep 2005 - 26 Feb 2006
 

Revision 192006-01-25 - TobyRodwell

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META TOPICPARENT name="WebHome"

Standard tests

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!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation
!C
Precedence cut-off in effect
Changed:
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![num]
displays the ICMP unreachable code, as defined in a variety of RFC, listed at http://www.spirit.com/Resources/icmp.html
>
>
![num]
displays the ICMP unreachable code, as defined in a variety of RFC, shown at http://www.iana.org/assignments/icmp-parameters
  Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. Some *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the -I flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

Revision 182006-01-25 - TobyRodwell

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META TOPICPARENT name="WebHome"

Standard tests

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!H
Host unreachable
!N
Network unreachable
!P
Protocol unreachable
Changed:
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<
!S
Source-route failed
>
>
!S
Source-route failed (that is to say, the router was not able to honour the source-route option set in an IP packet)
 
!F[pmtu]
Fragmentation needed. [pmtu] displays the Path MTU Discovery value, typically the "next-hop MTU" contained in the ICMP response packet.
!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation
!C
Precedence cut-off in effect
Changed:
<
<
![num]
displays the ICMP unreachable code, as defined in RFC 1812 Requirements for IP Version 4 Routers
>
>
![num]
displays the ICMP unreachable code, as defined in a variety of RFC, listed at http://www.spirit.com/Resources/icmp.html
  Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. Some *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the -I flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

Revision 172005-12-15 - SimonLeinen

Line: 1 to 1
 
META TOPICPARENT name="WebHome"

Standard tests

Line: 60 to 60
  Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behavour can actually limit TCP performance - if the last transfer was poor, then the starting TCP paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
Deleted:
<
<

Network Emulation

NISTnet and 'netem' are network emulation software that can be run on Linux machines. In particular, they can be used to introduce delays to packets, thereby simulating a long(er) distance network.

NistNet (Linux kernel 2.4 and older)
NetEm (Linux kernel 2.6 and newer)

 -- TobyRodwell - 06 Apr 2005 -- OrlaMcGann - 26 Jul 2005 -- OrlaMcGann - 14 Jul 2005

Revision 162005-11-14 - TobyRodwell

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META TOPICPARENT name="WebHome"

Standard tests

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  NISTnet and 'netem' are network emulation software that can be run on Linux machines. In particular, they can be used to introduce delays to packets, thereby simulating a long(er) distance network.
Changed:
<
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NistNet
NetEm
>
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NistNet (Linux kernel 2.4 and older)
NetEm (Linux kernel 2.6 and newer)
  -- TobyRodwell - 06 Apr 2005 -- OrlaMcGann - 26 Jul 2005

Revision 152005-10-10 - OrlaMcGann

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META TOPICPARENT name="WebHome"

Standard tests

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!H
Host unreachable
!N
Network unreachable
!P
Protocol unreachable
Changed:
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<
!S
Source-route failed
>
>
!S
Source-route failed
  !F [pmtu]: Fragmentation needed. [pmtu] displays the Path MTU Discovery value, typically the "next-hop MTU" contained in the ICMP response packet.
!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation

Revision 142005-09-20 - SimonLeinen

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META TOPICPARENT name="WebHome"

Standard tests

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traceroute

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Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range. If there is no response to the probe within a certain time period (typically 5ms), then a "*" is displayed.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occasionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.
>
>
Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range. If there is no response to the probe within a certain time period (typically 5ms), then a * is displayed.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occasionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an ! will be printed beside the RTT in the output.
  Other error messages that may appear after the RTT in the output of a traceroute are:
Line: 25 to 25
 
!N
Network unreachable
!P
Protocol unreachable
!S
Source-route failed
Changed:
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<
!F [pmtu]: Fragmentation needed. [pmtu] displays the Path MTU Discovery value
>
>
!F [pmtu]: Fragmentation needed. [pmtu] displays the Path MTU Discovery value, typically the "next-hop MTU" contained in the ICMP response packet.
 
!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation
!C
Precedence cut-off in effect

Revision 132005-09-18 - SimonLeinen

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META TOPICPARENT name="WebHome"
Deleted:
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-- TobyRodwell - 06 Apr 2005
 

Standard tests

Changed:
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Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies to determine the latency between those hosts. The output shows the Round Trip Time (RTT) between the host machine and the remote target. Ping is often used to determine whether a remote host is reachable. Unfortunately, it is quite common these days for ICMP traffic to be blocked by packet filters / firewalls, so a ping timing out does not necessarily mean that a host is unreachable.
Another method for checking remote host availability is to telnet to a port that you know to be accessible; such as port 80 (HTTP) or 25 (SMTP). If the connection is still timing out, then the host is probably not reachable; of course it is also possible that there is no service listening on that port. If a connection is made to the remote host, then it can be ended by typing the escape character (usually 'CTRL ^ ]') then 'quit'.
The "-f" flag may be specified to send ping packets as fast as they come back, or 100 times per second - whichever is more frequent. As this option can be very hard on the network only a super-user (the "root" account on *NIX machines) is allowed to specified this flag in a ping command.
The "-c" flag specifies the number of Echo request messages sent to the remote host by ping. If this flag isn't used, then the ping continues to send echo request messages until the user types "CTRL C". If the ping is cancelled after only a few messages have been sent, the RTT summary statistics that are displayed at the end of the ping output may not have finished being calculated and won't be completely accurate. To gain an accurate representation of the RTT, it is recommended to set a count of 100 pings. The MS Windows implementation of ping just sends 4 echo request messages by default.

>
>

ping

Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies to determine the latency between those hosts. The output shows the Round Trip Time (RTT) between the host machine and the remote target. Ping is often used to determine whether a remote host is reachable. Unfortunately, it is quite common these days for ICMP traffic to be blocked by packet filters / firewalls, so a ping timing out does not necessarily mean that a host is unreachable.

(Another method for checking remote host availability is to telnet to a port that you know to be accessible; such as port 80 (HTTP) or 25 (SMTP). If the connection is still timing out, then the host is probably not reachable - often because of a filter/firewall silently blocking the traffic. When there is no service listening on that port, this usually results in a "Connection refused" message. If a connection is made to the remote host, then it can be ended by typing the escape character (usually 'CTRL ^ ]') then quit.)

The -f flag may be specified to send ping packets as fast as they come back, or 100 times per second - whichever is more frequent. As this option can be very hard on the network only a super-user (the root account on *NIX machines) is allowed to specified this flag in a ping command.

The -c flag specifies the number of Echo request messages sent to the remote host by ping. If this flag isn't used, then the ping continues to send echo request messages until the user types CTRL C. If the ping is cancelled after only a few messages have been sent, the RTT summary statistics that are displayed at the end of the ping output may not have finished being calculated and won't be completely accurate. To gain an accurate representation of the RTT, it is recommended to set a count of 100 pings. The MS Windows implementation of ping just sends 4 echo request messages by default.

 Ping6 is the IPv6 implementation of the ping program. It works in the same way, but sends ICMPv6 Echo Request packets and waits for ICMPv6 Echo Reply packets to determine the RTT between two hosts. There are no discernable differences between the *NIX implementations and the MS Windows implementation.
Changed:
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traceroute

 Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range. If there is no response to the probe within a certain time period (typically 5ms), then a "*" is displayed.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occasionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.
Changed:
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 Other error messages that may appear after the RTT in the output of a traceroute are:
Changed:
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"!H" - Host unreachable
"!N" - Network unreachable
"!P" - Protocol unreachable
"!S" - Source-route failed
"!F [pmtu]" - Fragmentation needed. [pmtu] displays the Path MTU Discovery value
"!X" - Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
"!V" - Host precedence violation
"!C" - Precedence cut-off in effect
"! [num]" - displays the ICMP unreachable code, as defined in RFC 1812 Requirements for IP Version 4 Routers
"!" -


Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the "-I" flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

>
>
!H
Host unreachable
!N
Network unreachable
!P
Protocol unreachable
!S
Source-route failed !F [pmtu]: Fragmentation needed. [pmtu] displays the Path MTU Discovery value
!X
Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
!V
Host precedence violation
!C
Precedence cut-off in effect
! [num]: displays the ICMP unreachable code, as defined in RFC 1812 Requirements for IP Version 4 Routers

Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. Some *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the -I flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

  Traceroute6 uses the Hop-Limit field of the IPv6 protocol to elicit an ICMPv6 Time Exceeded ICMPv6 message from each gateway ("hop") along the path to some host. Just as with traceroute, it prints the route to the given destination and the RTT to each gateway/router.
The following are a list of possible errors that may appear after the RTT for a gateway (especially for OSes that use the KAME IPv6 network stack, such as the BSDs):
Changed:
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"!N" - No route to host
"!P" - Administratively prohibited (i.e. Blocked by a firewall, but the firewall issues an ICMPv6 message to the originating host to inform them of this)
"!S" - Not a Neighbour
"!A" - Address unreachable
"!" - The hop-limit is <= 1 on a Port Unreachable ICMPv6 message. This means that the packet got to it's destination, but that the reply only had a hop-limit large enough that was just large enough to allow it to get back to the source of the traceroute6. This option was more interesting in IPv4, where bugs in some implementations of the IP stack could be indentified by this behaviour.

Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the "-I" flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter / firewall.

>
>
!N
No route to host
!P
Administratively prohibited (i.e. Blocked by a firewall, but the firewall issues an ICMPv6 message to the originating host to inform them of this)
!S
Not a Neighbour
!A
Address unreachable
!
The hop-limit is <= 1 on a Port Unreachable ICMPv6 message. This means that the packet got to its destination, but that the reply only had a hop-limit large enough that was just large enough to allow it to get back to the source of the traceroute6. This option was more interesting in IPv4, where bugs in some implementations of the IP stack could be identified by this behaviour.

Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the -I flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter or firewall, while ICMP ECHO requests are permitted.

TCP Traceroute

 TCPTraceroute is a traceroute implementation that uses TCP packets instead of UDP or ICMP packets to send its probes. TCPtraceroute can be used in situations where a firewall blocks ICMP and UDP traffic. It is based on the "half-open scanning" technique that is used by NMAP, sending a TCP with the SYN flag set and waiting for a SYN/ACK (which indicates that something is listening on this port for connections). When it receives a response, the tcptraceroute program sends a packet with a RST flag to close the connection.
Changed:
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There are a number of other Traceroute Like Tools available for diagnosing network problems.
>
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There are a number of other Traceroute Like Tools available for diagnosing network problems.
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Linux Tools and Checks

Deleted:
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ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with 'ip route show cache'. Note, this learning behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
 
Added:
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ip route show cache

Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behavour can actually limit TCP performance - if the last transfer was poor, then the starting TCP paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.

 

Network Emulation

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 NISTnet and 'netem' are network emulation software that can be run on Linux machines. In particular, they can be used to introduce delays to packets, thereby simulating a long(er) distance network.

NistNet

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 NistNet
NetEm
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-- TobyRodwell - 06 Apr 2005
 -- OrlaMcGann - 26 Jul 2005
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 -- OrlaMcGann - 14 Jul 2005
Added:
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-- SimonLeinen - 18 Sep 2005
 

Revision 122005-08-11 - TobyRodwell

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005
Line: 54 to 54
 tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Linux Tools and Checks

Changed:
<
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ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are cahnged automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with 'ip route show cache'. Note, this learning behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
>
>
ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are changed automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with 'ip route show cache'. Note, this learning behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
 

Network Emulation

Revision 112005-07-27 - OrlaMcGann

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005
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 Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the "-I" flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter / firewall.

Added:
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>
TCPTraceroute is a traceroute implementation that uses TCP packets instead of UDP or ICMP packets to send its probes. TCPtraceroute can be used in situations where a firewall blocks ICMP and UDP traffic. It is based on the "half-open scanning" technique that is used by NMAP, sending a TCP with the SYN flag set and waiting for a SYN/ACK (which indicates that something is listening on this port for connections). When it receives a response, the tcptraceroute program sends a packet with a RST flag to close the connection.

 There are a number of other Traceroute Like Tools available for diagnosing network problems.

End-user tests

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 NistNet
NetEm
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-- OrlaMcGann - 26 Jul 2005
 -- OrlaMcGann - 14 Jul 2005

Revision 102005-07-18 - OrlaMcGann

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META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005
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 NistNet
NetEm
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-- OrlaMcGann - 14 Jul 2005

Revision 92005-07-14 - OrlaMcGann

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005

Standard tests

Changed:
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Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies. This shows the RTT (Round Trip Time) between the host machine and the remote target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually 'CTRL ^ ]') then 'quit'.

Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occaisionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.

>
>
Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies to determine the latency between those hosts. The output shows the Round Trip Time (RTT) between the host machine and the remote target. Ping is often used to determine whether a remote host is reachable. Unfortunately, it is quite common these days for ICMP traffic to be blocked by packet filters / firewalls, so a ping timing out does not necessarily mean that a host is unreachable.
Another method for checking remote host availability is to telnet to a port that you know to be accessible; such as port 80 (HTTP) or 25 (SMTP). If the connection is still timing out, then the host is probably not reachable; of course it is also possible that there is no service listening on that port. If a connection is made to the remote host, then it can be ended by typing the escape character (usually 'CTRL ^ ]') then 'quit'.
The "-f" flag may be specified to send ping packets as fast as they come back, or 100 times per second - whichever is more frequent. As this option can be very hard on the network only a super-user (the "root" account on *NIX machines) is allowed to specified this flag in a ping command.
The "-c" flag specifies the number of Echo request messages sent to the remote host by ping. If this flag isn't used, then the ping continues to send echo request messages until the user types "CTRL C". If the ping is cancelled after only a few messages have been sent, the RTT summary statistics that are displayed at the end of the ping output may not have finished being calculated and won't be completely accurate. To gain an accurate representation of the RTT, it is recommended to set a count of 100 pings. The MS Windows implementation of ping just sends 4 echo request messages by default.

Ping6 is the IPv6 implementation of the ping program. It works in the same way, but sends ICMPv6 Echo Request packets and waits for ICMPv6 Echo Reply packets to determine the RTT between two hosts. There are no discernable differences between the *NIX implementations and the MS Windows implementation.

Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range. If there is no response to the probe within a certain time period (typically 5ms), then a "*" is displayed.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occasionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.
 
Other error messages that may appear after the RTT in the output of a traceroute are:

Line: 18 to 26
 "!X" - Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
"!V" - Host precedence violation
"!C" - Precedence cut-off in effect
Changed:
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<
"! [num]" - displays the ICMP unreachable code, as defined in RFC 1812
>
>
"! [num]" - displays the ICMP unreachable code, as defined in RFC 1812 Requirements for IP Version 4 Routers
"!" -
 


Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the "-I" flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

Line: 35 to 44
 

Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the "-I" flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter / firewall.

Changed:
<
<

TracerouteLikeTools
>
>

There are a number of other Traceroute Like Tools available for diagnosing network problems.
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Revision 82005-07-14 - OrlaMcGann

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005

Standard tests

Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies. This shows the RTT (Round Trip Time) between the host machine and the remote target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually 'CTRL ^ ]') then 'quit'.
Changed:
<
<
Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range.
>
>
Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one for each probe sent until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range.
  The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occaisionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.
Changed:
<
<
Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the "-I" flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.
TracerouteLikeTools
>
>
Other error messages that may appear after the RTT in the output of a traceroute are:

"!H" - Host unreachable
"!N" - Network unreachable
"!P" - Protocol unreachable
"!S" - Source-route failed
"!F [pmtu]" - Fragmentation needed. [pmtu] displays the Path MTU Discovery value
"!X" - Administratively prohibited. The gateway prohibits these packets, but sends an ICMP message back to the source of the traceroute to inform them of this.
"!V" - Host precedence violation
"!C" - Precedence cut-off in effect
"! [num]" - displays the ICMP unreachable code, as defined in RFC 1812


Note that *NIX implementations of traceroute send UDP probe packets by default, whilst MS Windows tracert sends ICMP echo probes. *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the "-I" flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.

Traceroute6 uses the Hop-Limit field of the IPv6 protocol to elicit an ICMPv6 Time Exceeded ICMPv6 message from each gateway ("hop") along the path to some host. Just as with traceroute, it prints the route to the given destination and the RTT to each gateway/router.
The following are a list of possible errors that may appear after the RTT for a gateway (especially for OSes that use the KAME IPv6 network stack, such as the BSDs):

"!N" - No route to host
"!P" - Administratively prohibited (i.e. Blocked by a firewall, but the firewall issues an ICMPv6 message to the originating host to inform them of this)
"!S" - Not a Neighbour
"!A" - Address unreachable
"!" - The hop-limit is <= 1 on a Port Unreachable ICMPv6 message. This means that the packet got to it's destination, but that the reply only had a hop-limit large enough that was just large enough to allow it to get back to the source of the traceroute6. This option was more interesting in IPv4, where bugs in some implementations of the IP stack could be indentified by this behaviour.

Traceroute6 can also be specified to use ICMPv6 Echo messages to send the probe packets, instead of the default UDP probes, by specifying the "-I" flag when running the program. This may be useful in situations where UDP packets are blocked by a packet filter / firewall.

TracerouteLikeTools

 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Revision 72005-07-09 - OrlaMcGann

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005

Standard tests

Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies. This shows the RTT (Round Trip Time) between the host machine and the remote target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually 'CTRL ^ ]') then 'quit'.
Changed:
<
<
Traceroute Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. Note that either or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.
TracerouteLikeTools
>
>
Traceroute is used to determine the route a packet takes through the Internet to reach its destination; i.e. the number of "hops" it takes. UDP packets are sent as probes to a high ephemeral port (usually in the range 33434--33525) with the Time-To-Live (TTL) field in the IP header increasing by one until the end host is reached. The originating host listens for ICMP Time Exceeded responses from each of the routers/hosts en-route. It knows that the packet's destination has been reached when it receives an ICMP Port Unreachable message; we expect a port unreachable message as no service should be listening for connections in this port range.
The output of the traceroute program shows each host that the packet passes through on it's way to its destination and the RTT to each gateway en-route. Occaisionally, the maximum number of hops (specified by the TTL field, which defaults to 64 hops in *NIX implementations) is exceeded before the port unreachable is received. When this happens an "!" will be printed beside the RTT in the output.
Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. *NIX implementations of traceroute can be specified to use ICMP Echo messages instead of the default UDP probes, by using the "-I" flag. Note that either or both of ICMP and UDP may be blocked by firewalls, so this must be taken into account when troubleshooting.
TracerouteLikeTools
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Revision 62005-07-09 - OrlaMcGann

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005

Standard tests

Changed:
<
<
ping ICMP echo request and ICMP echo, shows the RTT (Round Trip Time) between the host machine and the target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually CNTL + ']') then 'quit'.
>
>
Ping sends ICMP echo request messages to a remote host and waits for ICMP echo replies. This shows the RTT (Round Trip Time) between the host machine and the remote target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually 'CTRL ^ ]') then 'quit'.
 
Changed:
<
<
traceroute Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. Note that either or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.
TracerouteLikeTools
>
>
Traceroute Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. Note that either or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.
TracerouteLikeTools
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Revision 52005-06-02 - AndrasJako

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005

Standard tests

Changed:
<
<
ping ICMP echo request and ICMP echo, shows the RTT (Round Trip Time) between the host machine and the target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (CNTL + ']' for Windows) then 'quit'
>
>
ping ICMP echo request and ICMP echo, shows the RTT (Round Trip Time) between the host machine and the target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (usually CNTL + ']') then 'quit'.
 
Changed:
<
<
traceroute Note that *NIX implementations of traceroute use UDP packets whilst MS Windows traceroute uses ICMP. Note that wither or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.
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traceroute Note that *NIX implementations of traceroute send UDP probe packets whilst MS Windows traceroute sends ICMP echo probes. Note that either or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.
TracerouteLikeTools
 

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Revision 42005-05-10 - TobyRodwell

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
-- TobyRodwell - 06 Apr 2005
Line: 15 to 15
 

Network Emulation

Changed:
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NISTnet and 'netem' are network emulation software that can be run on Linuix machines.
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NISTnet and 'netem' are network emulation software that can be run on Linux machines. In particular, they can be used to introduce delays to packets, thereby simulating a long(er) distance network.
  NistNet
NetEm

Revision 32005-04-14 - TobyRodwell

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
Deleted:
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 -- TobyRodwell - 06 Apr 2005

Standard tests

Line: 9 to 8
 traceroute Note that *NIX implementations of traceroute use UDP packets whilst MS Windows traceroute uses ICMP. Note that wither or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.

End-user tests

Changed:
<
<
tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-borowser making it a simple test for them to do.
>
>
tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.
 

Linux Tools and Checks

Changed:
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ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are cahnged automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus cn be showmn with 'ip route show cache'. Note, this learnign behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
>
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ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are cahnged automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with 'ip route show cache'. Note, this learning behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.
 
Added:
>
>

Network Emulation

NISTnet and 'netem' are network emulation software that can be run on Linuix machines.
 
Added:
>
>
NistNet
NetEm
 

Revision 22005-04-08 - TobyRodwell

Line: 1 to 1
 
META TOPICPARENT name="WebHome"
Deleted:
<
<
 -- TobyRodwell - 06 Apr 2005

Standard tests

Line: 10 to 9
 traceroute Note that *NIX implementations of traceroute use UDP packets whilst MS Windows traceroute uses ICMP. Note that wither or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.

End-user tests

Changed:
<
<
tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates.
>
>
tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-borowser making it a simple test for them to do.

Linux Tools and Checks

ip route show cache Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with 'ip route add|replace ...' whilst others are cahnged automatically by Linux in reponse to what it learns from TCP (such paramters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus cn be showmn with 'ip route show cache'. Note, this learnign behavour can actually limit TCP performance - if the last trasnfer was poor then the starting TPC paramters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.

 

Revision 12005-04-06 - TobyRodwell

Line: 1 to 1
Added:
>
>
META TOPICPARENT name="WebHome"

-- TobyRodwell - 06 Apr 2005

Standard tests

ping ICMP echo request and ICMP echo, shows the RTT (Round Trip Time) between the host machine and the target. It is quite common these days for ICMP traffic to be blocked, so pings timing out does not necessarily mean a host is unavailable. To check for connectivity an alternative is to telnet to a port which you know to be accessible. If the connection times out then the host is either not reachable or not listening on the port in question. If you can connect, then just break out of the session by typing the esacpe character (CNTL + ']' for Windows) then 'quit'

traceroute Note that *NIX implementations of traceroute use UDP packets whilst MS Windows traceroute uses ICMP. Note that wither or both of ICMP and UDP may be blocked by firewalls, so take this into account when troubleshooting.

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates.
 
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