Default routes on BGP routers with full feeds

Andreas Larsen andreas.larsen at
Wed Nov 5 06:49:39 UTC 2014

There is one setup where you would need default route from your provider.

If you have no IBGP between two sites and your prefix is a large /16 on side and maybe a /18 from that /16 on another site. These site would not be able to talk to each other if you orginate from the same AS.

Other than that I see not harm in having both default and a full table since longest prefix match will always win even if you have 2 or more transits.

// Andreas
Med vänlig hälsning
Andreas Larsen

IP-Only Telecommunication AB| Postadress: 753 81 UPPSALA | Besöksadress: S:t Persgatan 6, Uppsala |
Telefon: +46 (0)18 843 10 00 | Direkt: +46 (0)18 843 10 56<>

5 nov 2014 kl. 02:41 skrev Chris Rogers <crogers at<mailto:crogers at>>:

We don't accept a default from anyone, but will send one to a customer when
specifically requested.

We heavily filter all incoming routes (bogon, 1918, and many others). We
don't want data resorting to 0/0 and ::/0 when we specifically rejected the
matching route at the import policy.

Additionally, if your upstream isn't announcing a route to you, where are
they going to send your traffic anyway?

Chris Rogers
+1.302.357.3696 x2110

On Tue, Nov 4, 2014 at 5:42 PM, Owen DeLong <owen at> wrote:

It seems in such a case, the traffic still doesn’t know where to go, but
you don’t realize it because you have a default.

Then you pass the traffic to one of the providers who doesn’t have a route
for it and they drop it instead of you.

If you see something different, then, by definition, said provider is not
feeding you a full set of their tables, or, they, too, are depending on a
default and are not receiving a full set of tables.


On Nov 4, 2014, at 10:25 AM, Mike Walter <mwalter at> wrote:

I have 5 providers and we get the default from all of them and full
routing tables.

I have seen cases where if there is no default route, the traffic didn't
know where to go, even with full routes from all my providers.


-----Original Message-----
From: NANOG [mailto:nanog-bounces at] On Behalf Of Berry Mobley
Sent: Tuesday, November 04, 2014 12:47 PM
To: nanog at
Subject: Default routes on BGP routers with full feeds

I'm wondering how many of you who are multihomed also add default
routes pointing to your providers from whom you are receiving full feeds.

If so, why? If not, why not?



More information about the NANOG mailing list