rfc 1812 third party address on traceroute

William Herrin bill at herrin.us
Tue May 31 18:22:36 UTC 2016

On Tue, May 31, 2016 at 12:08 PM, Octavio Alvarez
<octalnanog at alvarezp.org> wrote:
>>                .-----------------.
>>                |                 |
>>                |               B |--------- D
>>     S ---------| A      R        |
>>                |               C |--------- (toward S)
>>                |                 |
>>                `-----------------'

> I'm not sure if you mean that, if sent through C it should have the
> source addres of A, or that it should actually be sent through A
> regardless of the routing table (which sounds better to me).


That doesn't make sense. There may be multiple next hops out A. If the
next hop in the FIB is out C, how would the router pick the next hop
to send to out A?

Anyway, Randy's comment was about source address selection, not
routing. With the packet coming from S into interface A, he'd prefer
that the ICMP error message be sourced from the IP address assigned to
A, not the IP address assigned to C or R.


William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>

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