On Tue, Jun 14, 2022 at 01:35:36PM +0300, Eugene Bogomazov wrote:
TL;DR: What are the best ways to include AFI/SAFI channel check during attribute creation?
Hi
RFC 9234 specifically clarifies that it can only be applied on IPv4/IPv6 unicast sessions. On all other sessions the OTC attribute should be decoded from and also transferred to such sessions without any change.
The problem is how to include AFI/SAFI checks in the code: 1) If we have information about a channel (as in *bgp_update_attrs*), we can simply run the following check proto/bgp/attrs.c if (bgp_channel_is_role_applicable(c)) { ... } proto/bpg/bgpd.h static inline int bgp_channel_is_role_applicable(struct bgp_channel *c) { return (c->afi == BGP_AF_IPV4 || c->afi == BGP_AF_IPV6); }
static inline int bgp_cc_is_role_applicable(struct bgp_channel_config *c) { return (c->afi == BGP_AF_IPV4 || c->afi == BGP_AF_IPV6); }
Yes. in bgp_update_attrs() it would make sense to add the check directly in such way.
2) However, in *bgp_decode_attrs *the AFI/SAFI information is only available after NLRI decoding. There is also a side approach with using *bgp_find_update_afi,* a static function from proto/bgp/packets.c to extract AFI/SAFI from a packet payload. The question is - what is the best way to extract AFI/SAFI information: apply OTC rules after NLRI is decoded (but where?) or change and reuse static bgp_find_update_afi (if possible) to get AFI/SAFI information before processing the OTC attribute?
Technically, one can receive an update message that has IPv4-unicast directly in ip_reach_nlri, and something different (e.g. VPNv4) in mp_reach_nlri. Although such messages are deprecated, they should still be accepted as valid. Therefore, one has to apply OTC rules to some NLRI and not to others. That is a similar issue like with bgp_next_hop, which may have different value for these two sets of NLRI. So perhaps you could handled that in bgp_finish_attrs() ?
3) But the biggest problem is with *bgp_preexport*. It uses bgp_proto, which doesn't use channel information when filtering routes with BGP specific rules. And I don't find a way to add this support to this filter. The question is - how to apply AFI/SAFI check for OTC attribute rules during bgp export and where is the best place to do so? Of course, if we want it to be like a predefined route-map.
We have a change in 3.0 branch to have channel argument in bgp_preexport(), we will rebase this change to master branch soon. So you can assume it will be there. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@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."