Problems configuring multihop BGP setup

22 Jul 2021

      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@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