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rfc 1812 third party address on traceroute
- Subject: rfc 1812 third party address on traceroute
- From: randy at psg.com (Randy Bush)
- Date: Mon, 30 May 2016 22:03:33 -0700
rfc1812 says
4.3.2.4 ICMP Message Source Address
Except where this document specifies otherwise, the IP source address
in an ICMP message originated by the router MUST be one of the IP
addresses associated with the physical interface over which the ICMP
message is transmitted. If the interface has no IP addresses
associated with it, the router's router-id (see Section [5.2.5]) is
used instead.
some folk have interpreted this to mean that, if a router R has three
interfaces
.-----------------.
| |
| B |--------- D
S ---------| A R |
| C |--------- (toward S)
| |
`-----------------'
if the source of a traceroute from S toward D with TTL to expire on R,
and R's FIB wants to exit via C to get back to S (yes, virginia, the
internet is highly asymmetric), the source address of the time exceeded
message should be C.
of course, simpletons such as i would desire the source of the time
exceeded message to be A. after all, this is the interface to which i
sent the icmp with the TTL to expire.
ras's preso,
https://www.nanog.org/meetings/nanog47/presentations/Sunday/RAS_Traceroute_N47_Sun.pdf
page 10 illustrates this issue with rfc1812
cursory research and talking with C & J seem to indicate that they do
what i want not what some folk have interpreted 1812 to mean. at least
on some models.
is anyone seeing the dreaded rfc1812 behavior in a citable fashion? how
common is it?
randy