From: Theo Buehler <tb@theobuehler.org>
Subject: Re: bgpd: rfc8654 extended message support
To: tech@openbsd.org
Date: Mon, 9 Dec 2024 10:34:04 +0100

On Tue, Dec 03, 2024 at 03:51:22PM +0100, Claudio Jeker wrote:
> Since we can handle imsg > 16k now we can also handle 64k BGP messages.
> So implement the bits for extended message support.
> 
> This should mostly follow rfc8654 with the following differences:
> 
> - NOTIFICATIONS are always truncated to fit in 4096 bytes. This is so that
>   early errors do not ship too large packets. Also I see little point in
>   having huge NOTIFICATIONS.
> 
> - I did not implement the SHOULD in:
>     When propagating that UPDATE onward to a neighbor that has not advertised
>     the BGP Extended Message Capability, the speaker SHOULD try to reduce the
>     outgoing message size by removing attributes eligible under the "attribute
>     discard" approach of [RFC7606].
>   bgpd does the withdraw of previous NLRI since a while. There are only a
>   few attributes that use "attribute discard" and in most cases their size
>   is not the problem (or we already discarded them on input). So
>   implementing that seems like a waste of time.
> 
> - I decided that bgpd only sends large messages if both sides announce
>   extended messages. In other words if the local bgpd has not set it then
>   no large message will be sent (even though the remote annouces it) so we
>   take the MAY in:
>     A BGP speaker MAY send BGP Extended Messages to a peer only if the BGP
>     Extended Message Capability was received from that peer.
> 
> I tested this against a modifed version of the maxattr.sh regress test.
> That part will be committed once this is in.

This seems to do what it says on the tin. I can't spot anything wrong with it.
Let's get this in.

ok tb

Two nits below.

> Index: usr.sbin/bgpd/bgpd.conf.5
> ===================================================================
> RCS file: /cvs/src/usr.sbin/bgpd/bgpd.conf.5,v
> diff -u -p -r1.242 bgpd.conf.5
> --- usr.sbin/bgpd/bgpd.conf.5	14 Aug 2024 19:09:51 -0000	1.242
> +++ usr.sbin/bgpd/bgpd.conf.5	3 Dec 2024 14:39:29 -0000
> @@ -1091,6 +1091,22 @@ The default is
>  .Ic no .
>  .Pp
>  .It Xo
> +.Ic announce extended
> +.Pq Ic yes Ns | Ns Ic no Ns | Ns Ic enforce
> +.Xc
> +If set to
> +.Ic yes ,
> +the extended message capability is announced.
> +If negotiated the default maximum message size is increaded from 4096 to 65535

Missing comma after negotiated.

[...]

> Index: usr.sbin/bgpd/parse.y
> ===================================================================

[...]

> @@ -3536,6 +3539,7 @@ lookup(char *s)
>  		{ "export",		EXPORT},
>  		{ "export-target",	EXPORTTRGT},
>  		{ "ext-community",	EXTCOMMUNITY},
> +		{ "extended",		EXTENDED },

other members have no space before },

>  		{ "fib-priority",	FIBPRIORITY},
>  		{ "fib-update",		FIBUPDATE},
>  		{ "filtered",		FILTERED},