Problems configuring multihop BGP setup

[Rainer Kulow]

Hello,

Thank you very much for your response.
Actually, this is just an extracted example from a larger setup to show the 
problem in a simpler way. Therefore, the use of BGP seems perhaps a bit 
superfluous here.

In fact, you were absolutely right with your guess.
Using
	protocol direct {
	        ipv4;
	}
everything works as desired.

Thanks,
Rainer

On 22-07-2021 18:23, Alexander Zubkov wrote:

> Hello,
>
> Why do you want your BGP sessions to be multihop? If you have direct links, 
> it is better if they are direct. From the first sight, you have "protocol 
> direct" disabled. This may cause your routes to be "unreachabe" and that is 
> why they are not propagated correctly.
>
> On Thu, Jul 22, 2021 at 4:13 PM Rainer Kulow <rainer.kulow at online.de> wrote:
> >
> > I'am sorry, the ascii graphic was somehow wrapped a bit strangely.
> >
> > Here is a better version of it (now using the correct AS-Numbers):
> >
> > +-----------------+
> > |  AS 60007    |
> > |10.70.0.1/16|
> > |                       |
> > +-------+--------+
> >             |  172.16.18.1/30
> >             |
> >             |  172.16.18.2/30
> > +-------+--------+
> > |  AS 60002    |
> > |10.20.0.1/16|
> > |                       |
> > +-------+--------+
> >            |  172.16.96.1/30
> >            |
> >            |  172.16.96.2/30
> > +-------+--------+
> > |  AS 60005    |
> > |10.50.0.1/16|
> > |                       |
> > +-----------------+
> >
> >
> > On 22-07-2021 15:43, Rainer Kulow wrote:
> > >Hello bird community,
> > >
> > >I am trying to establish complete connectivity using BGP in the
> > >following setup containing three AS with direct links:
> > >
> > >    172.16.18.1/30         172.16.18.2/30     172.16.96.1/30
> > >172.16.96.2/30
> > >+--------------+                                    +--------------+
> > >+--------------+
> > >| AS 60007 +---------------------------+ AS 60002
> > >+---------------------------+ AS 60005 |
> > >+--------------+                                    +--------------+
> > >+--------------+
> > >10.70.0.1/16                                   10.20.0.1/16
> > >10.50.0.1/16
> > >
> > >The goal is that every address from one of the /16 networks can reach
> > >all addresses in the other /16 networks.
> > >
> > >My current setup (here for the middle AS, the others are configured
> > >analogously):
> > >AS 60002 has three network cards, one with 172.16.18.2, one with
> > 172.16.96.1
> > >and one 10.20.0.1.
> > >
> > >log syslog all;
> > >router id 10.20.0.1;
> > >
> > ># interface scan every 10s
> > >protocol device {
> > >       scan time 10;
> > >}
> > >
> > ># no automaic generated direct routes to all network interfaces
> > >protocol direct {
> > >       disabled;
> > >}
> > >
> > ># synchronize BIRD routing tables with the OS kernel protocol kernel
> > >{
> > >        ipv4 {
> > >              import all;
> > >              export all;
> > >        };
> > >        merge paths on;
> > >}
> > >
> > ># static IPv4 routes
> > >protocol static static1{
> > >      ipv4;
> > >      route 10.20.0.0/16 via 10.20.0.1; }
> > >
> > ># BGP peers
> > >template bgp bgp_peer{
> > >      local as 60002;
> > >      multihop;
> > >
> > >      ipv4 {
> > >              import filter {
> > >                  if proto = "static1" then reject;
> > >                  accept;
> > >              };
> > >              export all;
> > >              next hop self;
> > >      };
> > >
> > >}
> > >
> > >protocol bgp a_b from bgp_peer {
> > >      description "BGP a-b";
> > >      neighbor 172.16.18.1 as 60007;
> > >}
> > >
> > >protocol bgp b_c from bgp_peer {
> > >      description "BGP b-c";
> > >      neighbor 172.16.96.2 as 60005;
> > >}
> > >
> > >
> > >If I delete "multihop" and "next hop self" from the template, I get
> > >all routes, but can only ever ping the closest AS.
> > >With "multihop" I also get all routes, but the routes to other AS are
> > marked
> > >as unreachable.
> > >I would be glad if someone could tell me how to realize this multihop
> > >scenario. It would also be interesting that the solution scales, so
> > >that I can hang, for example, more AS in the chain above.
> > >
> > >Thanks in advance,
> > >Best regards,
> > >Rainer
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