Re: rfc 1812 third party address on traceroute

[Hugo Slabbert <hugo () slabnet com>]

On Wed 2016-Jun-01 14:03:41 -0700, Octavio Alvarez <octalnanog () 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 () slabnet com
pgp key: B178313E   | also on Signal

Attachment: signature.asc
Description: Digital signature