Howdy!

Thank you for your patch. This is a real issue which we’d like to handle differently because your approach needs internal API changes.

We’ll instead refactor the BGP channel startup code to not start the channel at all; we need this anyway to allow future development.

Thank you again and have a nice day!

Maria

Internal reference: #447

On Thu, Jun 18, 2026 at 10:18:32AM -0400, Zhang Maiyun via Bird-users wrote:

Hello All,

I was hoping to get some feedback on this change. For example, bgp’s channel start function gives up when it cannot find a proper next hop, but the channel is still treated as successfully initialized. This then leads to lots of errors in bgp_decode_nlri about bad NH.

I think it might be a better idea to leave the channel in the DOWN state when this happens, and this patch allows the channel start function to reject the DOWN->START transition.

Best, Maiyun

On Thu, Jun 18, 2026 at 10:12:32AM -0400, me@maiyun.me wrote: > From: Zhang Maiyun me@maiyun.me >
> Signed-off-by: Zhang Maiyun me@maiyun.me > — > nest/proto.c | 27 ++++++++++++++++++++——- > proto/bgp/bgp.c | 2 +- > 2 files changed, 21 insertions(+), 8 deletions(-) >
> diff –git a/nest/proto.c b/nest/proto.c > index 4472fe6f..2edbe142 100644 > — a/nest/proto.c > +++ b/nest/proto.c > @@ -1086,7 +1086,7 @@ channel_setup_in_table(struct channel c) > } >
>
> -static void > +static int > channel_do_start(struct channel c) > { > c->proto->active_channels++; > @@ -1094,9 +1094,12 @@ channel_do_start(struct channel c) > if ((c->in_keep & RIK_PREFILTER) == RIK_PREFILTER) > channel_setup_in_table(c); >
> - CALL(c->class->start, c); > + if (c->class->start) > + if (c->class->start(c) != 0) > + return -1; >
> channel_start_import(c); > + return 0; > } >
> static void > @@ -1176,7 +1179,11 @@ channel_set_state(struct channel c, uint state) > ASSERT(cs == CS_DOWN || cs == CS_PAUSE); >
> if (cs == CS_DOWN) > - channel_do_start(c); > + if (channel_do_start(c) != 0) { > + // Reject the channel start and return to down state > + c->channel_state = CS_DOWN; > + c->last_state_change = current_time(); > + } >
> break; >
> @@ -1184,12 +1191,18 @@ channel_set_state(struct channel c, uint state) > ASSERT(cs == CS_DOWN || cs == CS_START || cs == CS_PAUSE); >
> if (cs == CS_DOWN) > - channel_do_start(c); > + if (channel_do_start(c) != 0) { > + // Reject the channel start and return to down state > + c->channel_state = CS_DOWN; > + c->last_state_change = current_time(); > + } >
> - if (!c->gr_wait && c->proto->rt_notify) > - channel_start_export(c); > + if (c->channel_state != CS_DOWN) { > + if (!c->gr_wait && c->proto->rt_notify) > + channel_start_export(c); >
> - channel_do_up(c); > + channel_do_up(c); > + } > break; >
> case CS_PAUSE: > diff –git a/proto/bgp/bgp.c b/proto/bgp/bgp.c > index 8d04a05d..1923a80d 100644 > — a/proto/bgp/bgp.c > +++ b/proto/bgp/bgp.c > @@ -3257,7 +3257,7 @@ bgp_channel_start(struct channel C) > if (ipa_zero(c->next_hop_addr)) > { > log(L_WARN “%s: Missing next hop address”, p->p.name); > - return 0; > + return -1; > } >
> /* Set link-local address for IPv6 single-hop BGP */ > –
> 2.54.0 >

–
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.