rfc 1812 third party address on traceroute

Wed Jun 1 21:08:37 UTC 2016

On Wed 2016-Jun-01 14:03:41 -0700, Octavio Alvarez <octalnanog at alvarezp.org> wrote:

>On 05/31/2016 11:22 AM, William Herrin wrote:
>>> 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?
>
>Back to the physical address that sent the TTL-offending packet.

Which comes back to my question:
What guarantees do you have that the device at that physical address (so, 
adjacent off of R's interface A) has a valid route for S, and that the 
route does not simply point back to R?

>> 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.
>
>Thanks.

-- 
Hugo Slabbert       | email, xmpp/jabber: hugo at slabnet.com
pgp key: B178313E   | also on Signal
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