Re: Support for dual AS and AS migration

[Ondrej Zajicek]

On Mon, Mar 05, 2018 at 07:22:22AM +0100, Tore Anderson wrote:
> * Lennert Buytenhek 
> 
> > Somewhat related to this, I wrote this patchset last year:
> > 
> > 
> > http://trubka.network.cz/pipermail/bird-users/2017-March/thread.html#11084
> > 
> > The idea was to let you configure two AS numbers that a remote peer
> > can connect to us with, so that the remote peer can be reconfigured
> > to use a different AS number without the local machine needing to
> > reconfigured at the same time.
> > 
> > If there's interest in this patchset I can dust it off and try
> > resubmitting it.
> 
> Hi Lennert,
> 
> In case you do decide to work on this again, I'd suggest you take a
> look at the FRR / Cumulus feature where you can configure a
> peer/peer-groups ASN to be the string «external». This means to accept
> the peer to be in any arbitrary ASN (except for the local one).
> 
> I've found this to be a very convenient feature, and it'd be nice to
> see it in BIRD too.

Hi

The original patchset allowed accepting both internal and external BGP
sessions on one BGP instance, which makes it more complicated that just
accepting multiple AS numbers. Esp. with BIRD 2.0.1, which supports also
BGP confederations and therefore has three discinct kinds of BGP
sessions.

I think that reasonable interface would be to allow to specify the number
set (of allowed AS numbers), like is used in filters, but still keep it
limited to one kind (internal, external, inter-confederation) of BGP sessions.

Such feature we would accept or perhaps i will implement it someday.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santi...@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."

Re: Support for dual AS and AS migration

[Tore Anderson]

* Lennert Buytenhek 

> Somewhat related to this, I wrote this patchset last year:
> 
>   
> http://trubka.network.cz/pipermail/bird-users/2017-March/thread.html#11084
> 
> The idea was to let you configure two AS numbers that a remote peer
> can connect to us with, so that the remote peer can be reconfigured
> to use a different AS number without the local machine needing to
> reconfigured at the same time.
> 
> (The converse case, where the local machine will reconnect with a
> secondary AS number if connecting with the primary AS number fails is
> more involved, and in my use case, I control both endpoints anyway,
> so this was sufficient.)
> 
> If there's interest in this patchset I can dust it off and try
> resubmitting it.

Hi Lennert,

In case you do decide to work on this again, I'd suggest you take a
look at the FRR / Cumulus feature where you can configure a
peer/peer-groups ASN to be the string «external». This means to accept
the peer to be in any arbitrary ASN (except for the local one).

I've found this to be a very convenient feature, and it'd be nice to
see it in BIRD too.

https://docs.cumulusnetworks.com/display/DOCS/Border+Gateway+Protocol+-+BGP#BorderGatewayProtocol-BGP-ConfiguringBGPPeeringRelationshipsacrossSwitches

Tore

Re: Support for dual AS and AS migration

[Lennert Buytenhek]

Somewhat related to this, I wrote this patchset last year:


http://trubka.network.cz/pipermail/bird-users/2017-March/thread.html#11084

The idea was to let you configure two AS numbers that a remote peer
can connect to us with, so that the remote peer can be reconfigured
to use a different AS number without the local machine needing to
reconfigured at the same time.

(The converse case, where the local machine will reconnect with a
secondary AS number if connecting with the primary AS number fails is
more involved, and in my use case, I control both endpoints anyway,
so this was sufficient.)

If there's interest in this patchset I can dust it off and try
resubmitting it.



On Sun, Feb 18, 2018 at 01:25:37PM +, Adam Król wrote:

> Does BIRD have any support for AS migration mechanism as mentioned in RFC7705 
> https://tools.ietf.org/html/rfc7705? Something like 
> https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16/irg-xe-16-book/bgp-support-for-dual-as-configuration-for-network-as-migrations.html?
> 
> I know it can be achieved by functions, but maybe there is already simplier 
> way to get this done.
> 
> Best regards,
> Adam Król
> 

Re: Support for dual AS and AS migration

[Marco d'Itri]

On Feb 18, Ondrej Zajicek  wrote:

> When route is exported to a BGP peer, BIRD prepends ASN based on ASN of
> exporting BGP protocol instance. Therefore, only one ASN is prepended to
> AS path automatically. If you want to have both AS numbers in AS path,
> you would have to use filters.
This is not about prepending, but about being able to negotiate the 
session using either of two different ASNs.

-- 
ciao,
Marco


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Re: Support for dual AS and AS migration

[Ondrej Zajicek]

On Sun, Feb 18, 2018 at 05:00:36PM +, Adam Król wrote:
> Is there any description how does AS path look like in that kind of 
> configuration?
> 
> Let's consider that scheme:
> 
> PEER A<-> ISP (bird - one instance)   <-> 
> PEER B
> AS 65499  <->  AS 65505   AS 65510<-> AS 65496
> 
> How side A see side B? Bird adds all AS numbers of ISP to AS path?

Hi

When route is exported to a BGP peer, BIRD prepends ASN based on ASN of
exporting BGP protocol instance. Therefore, only one ASN is prepended to
AS path automatically. If you want to have both AS numbers in AS path,
you would have to use filters.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santi...@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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RE: Support for dual AS and AS migration

[Adam Król]

Is there any description how does AS path look like in that kind of 
configuration?

Let's consider that scheme:

PEER A  <-> ISP (bird - one instance)   <-> PEER B
AS 65499<->  AS 65505   AS 65510<-> AS 65496

How side A see side B? Bird adds all AS numbers of ISP to AS path?

Best regards,
Adam Król

-Original Message-
From: Bird-users [mailto:bird-users-boun...@network.cz] On Behalf Of Marco 
d'Itri
Sent: Sunday, February 18, 2018 5:23 PM
Cc: bird-users@network.cz
Subject: Re: Support for dual AS and AS migration

On Feb 18, Alarig Le Lay <ala...@swordarmor.fr> wrote:

> You can choose the local AS on each BGP protocol instance, is it 
> sufficient?
No, because this still required coordinating the exact time of the AS change 
with each neighbor.

--
ciao,
Marco

Re: Support for dual AS and AS migration

[Marco d'Itri]

On Feb 18, Alarig Le Lay  wrote:

> You can choose the local AS on each BGP protocol instance, is it
> sufficient?
No, because this still required coordinating the exact time of the AS 
change with each neighbor.

-- 
ciao,
Marco


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Re: Support for dual AS and AS migration

[Alarig Le Lay]

On dim. 18 févr. 13:25:37 2018, Adam Król wrote:
> Does BIRD have any support for AS migration mechanism as mentioned in
> RFC7705 https://tools.ietf.org/html/rfc7705? Something like
> https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16/irg-xe-16-book/bgp-support-for-dual-as-configuration-for-network-as-migrations.html?
> 
> I know it can be achieved by functions, but maybe there is already
> simplier way to get this done.

Hi,

You can choose the local AS on each BGP protocol instance, is it
sufficient?

-- 
alarig


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