Community for small IX - problem with 4B ASN

Mon Jan 22 14:53:46 CET 2018

On Mon, Jan 22, 2018 at 2:00 PM, Piotr Marciniak <zboj at mnc.pl> wrote:

> Dear Advisors ;],
>
> Thank you for all posts. But still I do not know how to make Bird working
> with 4B communities and if I may do this - whether it will be accepted for
> our peers? In short - I do not know how to adapt to 4B communities
> following examples:
>
> https://gitlab.labs.nic.cz/labs/bird/wikis/Route_server_with
> _community_based_filtering_and_multiple_RIBs
> https://gitlab.labs.nic.cz/labs/bird/wikis/Route_server_with
> _community_based_filtering_and_single_RIB
>
> Is there any way to enable 4B communities in bird.conf?
>
> I do not have any problem with 4B ASn. I set bgp peering sessions from
> Bird with 4B ASn. Even our IX has AS205082.
>
> This is why I put 2 questions:
>
> 1. Is it possible to enable 4B ASn for communities in Bird? Will it work
> with other rouers?
>

This is not bird thing. You can not use 4B AS numbers with "old"
communities.
http://bird.network.cz/?get_doc&v=16&f=bird-5.html#ss5.2
pair

This is a pair of two short integers. Each component can have values from 0
to 65535. Literals of this type are written as (1234,5678). The same syntax
can also be used to construct a pair from two arbitrary integer expressions
(for example (1+2,a)).
But there is newer version of communities called large communities: lc

This is a specialized type used to represent BGP large community values. It
is essentially a triplet of 32bit values, where the first value is reserved
for the AS number of the issuer, while meaning of remaining parts is
defined by the issuer. Literals of this type are written as (123, 456, 789),
with any integer values. Similarly to pairs, LCs can be constructed using
expressions for its parts, (e.g. (myas, 10+20, 3*10), where myas is an
integer variable).
http://largebgpcommunities.net/
Those can be used with 4B AS numbers, but not every router supports them.

> 2. Can we use instead private ASn just for community filters? Are they
> processed corretly by other Internet routers of our peers?
>

You can use whatever numbers you want. AS numbers are used there for
clarity and interoperability. But it is rare needed to share communities
between operators.

>
> Please - do not explain me theoretical difference between 16 and 32 bits.
> Question is simple - can I use 4B communities for filters? If not - what
> 16bit "fake ASn" I can use instead safely?
>

So if you know the difference between 16 and 32 bits, than why you
surprised that you can not put 32-bit number into 16-bit entity? :)

>
> Best wishes,
>
> Piotr Marciniak
>
>
> -----Oryginalna wiadomość----- From: Paweł Nastachowski
> Sent: Monday, January 22, 2018 1:12 PM
> To: Piotr Marciniak
> Cc: bird-users at network.cz
> Subject: Re: Community for small IX - problem with 4B ASN
>
> Hi Piotr,
>
> I should use extended community for 4B ASN, because normal community is
> too small “Encodes a 32-bit value displayed as “16-bit ASN:16-bit value”.
>
> Regards,
> Pawel
>
> -----Wiadomość oryginalna-----
> Od: Bird-users <bird-users-bounces at network.cz> w imieniu użytkownika
> Piotr Marciniak <zboj at mnc.pl>
> Data: poniedziałek, 22 stycznia 2018 11:15
> Do: "bird-users at network.cz" <bird-users at network.cz>
> Temat: Community for small IX - problem with 4B ASN
>
>    Hello,
>
>    I've spent a while on below docs and faced a problem with 4B ASN we use.
>    Bird reports an error 'when 'myas' is 4B => so above 65535.
>    See some testing example below:
>
>    bird> configure
>    Reading configuration from /etc/bird/bird.conf
>    /etc/bird/bird.conf, line 81: Value 165250 out of range (0-65535)
>
>    The only way this config reports no error is to set here private ASn -
> fe.
>    65250. But it will never match our real ASn.
>
>    Two questions:
>
>    1. Is it possible to enable 4B ASn for communities in Bird? Will it work
>    with other rouers?
>    2. Can we use instead private ASn just for community filters? Are they
>    processed corretly by other Internet routers of our peers?
>
>    Or maybe there is another work around?
>
>    Best wishes,
>
>    Peter
>
>
>    -----Oryginalna wiadomość-----
>    From: Piotr Marciniak
>    Sent: Friday, December 29, 2017 5:01 PM
>    To: Ondrej Zajicek
>    Cc: bird-users at network.cz
>    Subject: Re: Community for small IX
>
>
>    There are some examples in BIRD wiki, mainly:
>
>    https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__gitlab.labs.nic.cz_labs_bird_wikis_Route-5Fserver-
> 5Fwith-5Fcommunity-5Fbased-5Ffiltering-5Fand-5Fmultiple-5FRI
> Bs&d=DwIDaQ&c=gxW9PgscCAGwFImBgfkGkoANogu61GVPNv0sglxAtik&r=
> 5Q01PsGCLGh5Iipn2_EFz2pKmXKRl5oJ_tHzyrwTUhrj4D27CXd9SGXgnGWo
> H5Yy&m=b6e1rT2mu_bWkZiOT-71FnOGwrXSx-xnpaRwbI3-BFI&s=2UgZOD_
> Fkqt6ZgVqlXm_vXRiY1LP_MTlkWo-TGVqAtE&e=
>    https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__gitlab.labs.nic.cz_labs_bird_wikis_Route-5Fserver-
> 5Fwith-5Fcommunity-5Fbased-5Ffiltering-5Fand-5Fsingle-5FRIB&
> d=DwIDaQ&c=gxW9PgscCAGwFImBgfkGkoANogu61GVPNv0sglxAtik&r=5Q0
> 1PsGCLGh5Iipn2_EFz2pKmXKRl5oJ_tHzyrwTUhrj4D27CXd9SGXgnGWoH5Y
> y&m=b6e1rT2mu_bWkZiOT-71FnOGwrXSx-xnpaRwbI3-BFI&s=KjVYea-iJR
> Nl8BxFQFgkEeHLWFK8qwenAm_GRJDH4Q4&e=
>
>    --
>    Elen sila lumenn' omentielvo
>
>    Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
>    OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
>    "To err is human -- to blame it on a computer is even more so."
>
>
>
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