best practice for advertising peering fabric routes

Michael Still stillwaxin at
Wed Jan 15 19:04:52 UTC 2014

On Wed, Jan 15, 2014 at 1:26 PM, William Herrin <bill at> wrote:
> On Wed, Jan 15, 2014 at 12:54 PM, Niels Bakker <niels=nanog at> wrote:
>> * nanog at (Jim Shankland) [Wed 15 Jan 2014, 18:04 CET]:
>>> So ... RFC1918 addresses for the IXP fabric, then?
>>> (Half kidding, but still ....)
>> They need to be globally unique.
> Hi Niels,
> Actually, they don't. To meet the basic definition of working, they
> just have to be able to originate ICMP destination unreachable packets
> with a reasonable expectation that the recipient will receive those
> packets. Global uniqueness is not required for that. However, RFC1918
> addresses don't meet the requirement for a different reason: they're
> routinely dropped at AS borders, thus don't have an expectation of
> reaching the external destination.
> Of course working, monitorable and testable are three different
> things. If my NMS can't reach the IXP's addresses, my view of the IXP
> is impaired. And "the Internet is broken" is not a trouble report that
> leads to a successful outcome with customer support... it helps to be
> able to pin things down with some specificity.
> Regards,
> Bill Herrin

Using RFC1918 would incur the assumption that one will need to use a
unique router or routing instance for every exchange connected to
since exchanges are likely to have overlapping space at that point
(RFC1918 IXP registry anyone?).   I don't think it'd be a good idea to
go down that path..

Also mentioned in a past nanog was the idea of potentially getting
someone like team cymru to setup all exchange prefixes in a special
bogon list and you could null route on your edge all those prefixes..
I inquired to team cymru about this back when originally discussed but
never got anywhere with them.

> --
> William D. Herrin ................ herrin at  bill at
> 3005 Crane Dr. ...................... Web: <>
> Falls Church, VA 22042-3004

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