Community for small IX - problem with 4B ASN

[Mikhail Grishin]

Hi Piotr ,
May be the most simple thing - to change your ASN number to 16bit - in 
case if solid % of your customers support and use only traditional 
communities (RFC 1997) .

RIPE can help.

Piotr Marciniak пишет 22.01.2018 18:46:
> Hello Ondrej,
>
> I am seeking for a way to make our small local IXP project to be a bit 
> more flexible and safe. I think we could do with implementation of 
> communities which would allow our peers to prepend or block their 
> prefixes from annoncing to specific peer or all peers.
>
> Goal is simple. Peer A should be able to send to us community to 
> prepend or block announcing his prefixes to chosen by ASn Peer B or 
> all peers.
>
> Which community standard I would like to use? Most supported on 
> typical, (mosttly) local ISP BGP routers - from Mikrotik by Cisco to 
> Bird. I do not think it is extraordinary wish. ;-] Rather typical for 
> most IXP of any size.
>
> In our scenario we rather do not need to forward communities. Just to 
> collect info from Peer A what to do with his prefixes before 
> announcing it to others.
>
> I think the only problem I am facing now is that I can't use in known 
> config examples our AS205082. But here we face another problem if I 
> understand correcttly - what to do if not only our community is 4B? I 
> may "shrink our" to any 16-bit equivalent like 65250 I use in my 
> examples. But stil if I have a peer with AS123456 - how to accept his 
> 4B AS in communities received from our peers? Fe. old Cisco can 
> connect to 4B ASn but can't work on 4B communities I think. So it 
> can't send me request - do not announce us to AS123456.
>
> But I think second problem is not very important for me. If someone 
> cannot send 4B community so.. it is a pitty for him. My problem is to 
> let people know what we can accept and process if they wish and can 
> send us their preferences. Thus - I need to work with 4B communities 
> in most common way possible.
>
> So yes - I would be happy to find an example which would work with 4B 
> extended communities both - for myas and peeras sides. If I am right 
> with SIXT example - bgp_ext_community are supported for peeras? If yes 
> - the only problem is myas which still can't be 4B. But I may replace 
> it with fake-16bit-pseudo-myas ;-]. All should be working then?
>
> Best wishes,
>
> Peter
>
>
>
> -----Oryginalna wiadomość----- From: Ondrej Zajicek
> Sent: Monday, January 22, 2018 4:16 PM
> To: Piotr Marciniak
> Cc: bird-users at network.cz
> Subject: Re: Community for small IX - problem with 4B ASN
>
> Well, that depends on exact meaning of 'communities'. There are three
> different independent community attributes:
>
> - 'traditional' communities (RFC 1997)
> - Extended communities (RFC 4360)
> - Large communities (RFC 8092)
>
> Attribute bgp_community is for traditional communities, which are limited
> to 16 bit components. So you cannot use 32bit ASNs with them. Also, even
> if you used 16bit private ASN as myas, you cannot use them for 32bit
> peeras.
>
> You can use Extended communities (and that is usual setting in IXes),
> but they can have one component 32 bit, but not both. So if you have
> 16bit myas, you could have 32bit peeras.
>
> Or you can use new Large communities, which are fully 32bit, and ditch
> both traditional and Extended communities. But this is pretty new
> standard and i am not sure how widely is supported by other systems.
>