google ipv6 routes via cogent

Patrick W. Gilmore patrick at
Sat Mar 4 18:37:30 UTC 2017

On Mar 3, 2017, at 9:05 PM, Job Snijders <job at> wrote:
> On Fri, Mar 03, 2017 at 09:42:04AM -0500, Patrick W. Gilmore wrote:
>> On Mar 3, 2017, at 7:00 AM, Nick Hilliard <nick at> wrote:
>>> Niels Bakker wrote:
>>>> As I explained in the rest of my email that you conveniently didn't
>>>> quote, it's so that you can selectively import routes from all your
>>>> providers in situations where your router cannot handle a full table.
>>> it can also break horribly in situations where the provider is providing
>>> "transit" but doesn't provide full transit.
>>> OTOH, if you are single-homed, it is highly advisable to accept a
>>> default, the reason being that most transit providers provide bgp
>>> communities with "don't advertise to customers" semantics.  So if you're
>>> single-homed and use a full dfz feed without default route, you will not
>>> have full connectivity to all the routes available from the transit
>>> provider.
> Correct.
>> If you are single-homed, there is no need for BGP at all.
> That is very strongly worded, and in plenty of cases a false assertion.
>> And injecting your ASN into the table is probably not terribly useful
>> to everyone else’s FIB.
> ASNs don't have anything to do with FIB.
>> There are, of course, corner cases. But in general, single-homed
>> people shouldn’t be using BGP.
> There are numerous reasons to use BGP when single-homed:
>    - as preparation to multi-home in the (near) future
>    - ability to quickly change providers
>    - to use BGP based blackholing features
>    - to save time on provisioning work (adding new prefixes becomes a
>      matter of just announcing and updating IRR/RPKI).
>    - loadbalanacing / loadsharing across multiple links
>    - ability to use bgp communities for traffic engineering
> In other words, if you have your own IP space, I'd recommend to get your
> own ASN and use BGP.

First, I said specifically there are corner cases. Everything you say above is a corner case. The sum of everyone in need of the above is to the right of the decimal compared to all single homed networks. Limiting it to “it you have your own IP space” makes the set even smaller.

You are also reaching here. Preparation for multi-homing in the near future is just multi-homing. Adding prefixes is a very occasional thing, and in some cases is actually not easier with BGP. (Ever worked with some provider’s IRR implementation?) Etc.

End of day, if you have your own space and only allow aggregates into the DFZ, even as a stub behind someone else, it doesn’t really save RIB slots compared to having the upstream announce it for you. My problem is making the exceptions sound normal. They are not, and we should not treat them as if they are. Else we will end up with people wanting to do it who do not understand what they are doing, polluting the table, etc.

I stand by my statement. Single Homed Networks Should Not Use BGP. It is a good general rule. There are exceptions, but the exceptions are rare and should be approached with caution & clue.


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