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bgpd: Confederation fixes with remote-as external/internal (backport #12861) #12873

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merged 2 commits into from
Feb 22, 2023
Merged

bgpd: Confederation fixes with remote-as external/internal (backport #12861) #12873

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ef6f761
bgpd: Pass global ASN for confederation peers if not AS_SPECIFIED
ton31337 Feb 21, 2023
55189a8
tests: Check if BGP confederation works with AS_EXTERNAL (!AS_SPECIFIED)
ton31337 Feb 21, 2023
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bgpd: Pass global ASN for confederation peers if not AS_SPECIFIED 
When we specify remote-as as external/internal, we need to set local_as to
bgp->as, instead of bgp->confed_id. Before this patch, (bgp->as != *as) is
always valid for such a case because *as is always 0.

Also, append peer->local_as as CONFED_SEQ to avoid other side withdrawing
the routes due to confederation own AS received and/or malformed as-path.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>
(cherry picked from commit db5a5ee)
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@ton31337 @mergify
ton31337 authored and mergify[bot] committed Feb 22, 2023
commit ef6f76144beb88a3bc0a382d3c923eb2997ccfea
26 changes: 24 additions & 2 deletions bgpd/bgp_attr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1655,6 +1655,14 @@ static enum bgp_attr_parse_ret bgp_attr_aspath_check(struct peer *const peer,
*/
struct aspath *aspath;

/* Refresh peer's type. If we set e.g.: AS_EXTERNAL/AS_INTERNAL,
* then peer->sort remains BGP_PEER_EBGP/IBGP, hence we need to
* have an actual type before checking.
* This is especially a case for BGP confederation peers, to avoid
* receiving and treating AS_PATH as malformed.
*/
(void)peer_sort(peer);

/* Confederation sanity check. */
if ((peer->sort == BGP_PEER_CONFED
&& !aspath_left_confed_check(attr->aspath))
Expand Down Expand Up @@ -4347,8 +4355,22 @@ bgp_size_t bgp_packet_attribute(struct bgp *bgp, struct peer *peer,
aspath = aspath_delete_confed_seq(aspath);

if (CHECK_FLAG(bgp->config, BGP_CONFIG_CONFEDERATION)) {
/* Stuff our path CONFED_ID on the front */
aspath = aspath_add_seq(aspath, bgp->confed_id);
/* A confed member, so we need to do the
* AS_CONFED_SEQUENCE thing if it's outside a common
* administration.
* Configured confederation peers MUST be validated
* under BGP_PEER_CONFED, but if we have configured
* remote-as as AS_EXTERNAL, we need to check again
* if the peer belongs to us.
*/
if (bgp_confederation_peers_check(bgp, peer->as)) {
aspath = aspath_dup(attr->aspath);
aspath = aspath_add_confed_seq(aspath,
peer->local_as);
} else {
/* Stuff our path CONFED_ID on the front */
aspath = aspath_add_seq(aspath, bgp->confed_id);
}
} else {
if (peer->change_local_as) {
/* If replace-as is specified, we only use the
Expand Down
6 changes: 3 additions & 3 deletions bgpd/bgpd.c
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Expand Up @@ -2027,9 +2027,9 @@ int peer_remote_as(struct bgp *bgp, union sockunion *su, const char *conf_if,

/* If the peer is not part of our confederation, and its not an
iBGP peer then spoof the source AS */
if (bgp_config_check(bgp, BGP_CONFIG_CONFEDERATION)
&& !bgp_confederation_peers_check(bgp, *as)
&& bgp->as != *as)
if (bgp_config_check(bgp, BGP_CONFIG_CONFEDERATION) &&
!bgp_confederation_peers_check(bgp, *as) && *as &&
bgp->as != *as)
local_as = bgp->confed_id;
else
local_as = bgp->as;
Expand Down