From: Huan Pham (huan.pham@valuenet.com.au)
Date: Wed Jan 23 2008 - 05:16:14 ARST
Hi Balaji,
Host that initiate traceroute send UDP packets with unique increasing
source/destination ports.
The ICMP message sent from intermediate router has a field that contains 64
bits of original UDP packets (sent by the host/router originating
traceroute). That should include UDP source/destination port numbers, that
can be used to differentiate among different traceroute sessions, and UDP
packets among each trace session.
Please see the RFC for more clarification:
ftp://ftp.rfc-editor.org/in-notes/rfc792.txt
Destination Unreachable ICMP Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internet Header + 64 bits of Original Data Datagram |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The internet header plus the first 64 bits of the original
datagram's data. This data is used by the host to match the
message to the appropriate process. If a higher level protocol
uses port numbers, they are assumed to be in the first 64 data
bits of the original datagram's data.
Cheers,
Huan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
BALAKRISHNAN Balaji
Sent: Wednesday, 23 January 2008 10:02 AM
To: ccielab@groupstudy.com
Subject: Traceroute question
Group,
I have a question on the traceroute. When doing the traceroute,
intermediate routers sends back the ICMP "time exceeded" reply with its
own source-ip. How the router could correlate this reply to the
original trace route request ?? I could be sending multiple
simultaneous traceroutes ! What is the mechanism used here that makes
router to correlate the icmp exceeded reply coming from an intermediate
router to a specific trace-route request ??
- Bala.
This archive was generated by hypermail 2.1.4 : Fri Feb 01 2008 - 10:38:01 ARST