Customers announcing communities to SP of SP

Hi,

Consider the following scenario:

- Customer A is a customer of SP A
- SP A is a customer of SP B
- SP B has a traffic engineering community implementation

With regards to using BGP communities for TE:

- Does SP A write their own community implementation that maps to (some portion of) the community implementation of SP B?
- Does SP A write their own community implementation that has no mappings at all to the community implementation of SP B; any TE that is required to be pushed to SP B is done by some dialog and coordination between Customer A and SP A?
- Does SP A allow Customer A to announce prefixes tagged with SP B’s communities[1][2]
- Is this sort of thing really complicated today, but one of the goals of draft-heitz-idr-large-community?

[1] Customer A has knowledge of SP A’s upstream SP B
[2] This opens up a can of worms where SP A or SP B implements some communities prefixed with reserved ASes, so we’ll assume that SP A implements some method of allowing communities prefixed with ASes of SP A and SP B only.

Thanks!

In a previous $dayjob at a different ASN I was customers of a large-ish
regional Canadian carrier (at 100M), and also of a small local guy (at 8M)
with only Cogent upstream. I would prepend out the local guy 3x, and then I
also tagged 174:3003 to have cogent prepend 3x more. This worked somewhat
OK to make up for the inbalance in speeds.

This type of use case is supported by, and works well with
draft-heitz-idr-large-community. As an operator of a 32-bit ASN I have no
ability to use communities with my ASN in them like 16-bit ASN operator
could, and I have expressed so on the IETF IDR list.

Theodore Baschak - AS395089 - Hextet Systems
https://ciscodude.net/ - https://hextet.systems/
http://mbix.ca/

Hi Jason,

The following reply which I sent to the IDR mailing list might also be
helpful for you to understand the way most of these designs currently
work - as well as some of the problems we encounter with the existing
RFC1997 communities:

http://www.ietf.org/mail-archive/web/idr/current/msg16219.html

draft-heitz-idr-large-community should tackle the missing 32-bit ASN
feature, but should also resolve the private AS overlapping problem
you're describing in [2] since it's a 32:32:32 format rather than 16:16.

Best regards,
Martijn Schmidt

Hi,

Consider the following scenario:

- Customer A is a customer of SP A
- SP A is a customer of SP B
- SP B has a traffic engineering community implementation

With regards to using BGP communities for TE:

- Does SP A write their own community implementation that maps to (some portion of) the community implementation of SP B?
- Does SP A write their own community implementation that has no mappings at all to the community implementation of SP B; any TE that is required to be pushed to SP B is done by some dialog and coordination between Customer A and SP A?
- Does SP A allow Customer A to announce prefixes tagged with SP B???s communities[1][2]

"Sometimes" for all of the above; it depends on the network. There are
networs which strip all signalling but their own. There are those who
will strip signalling to their immediate neighbors (expecting customers
to use thri own). There are some which propagate anything and everything.

IME, it is generally good to sanitize an input stream of signalling you
use to reduce unknown/difficult to trace conditions. It is also a good
principle for a sender to be aware of how far their dollars/euros/quatloos
propagate, as that's pretty much the limit of guarantee others will act
on their requests. In your scenario, when SP B changes their communities,
they have no obligation (nor method) to let a downstream of a downstream
know about it...

- Is this sort of thing really complicated today, but one of the
goals of draft-heitz-idr-large-community?

It can be complicated - review the various way folks have published
their policies via the compilation up at https://onestep.net/communities/
and you'll see a number of approaches. I can't speak for the authors,
but by my reading draft-heitz-idr-large-community provides two things:
- parity for 32b and 16b use in communities
- the room to clearly express multiple party ASNs distinctly from
  'take action' data, which we do not have now

Cheers!

Joe