iBGP advertisements

[isabelpgv1]

Hello,

I'm having a problem trying to advertise from one bgp AS  to two other routers with different bgp AS.   if you see the image below, R2 is on AS 64520 and R1 and R3 are in AS 64550.   I'm starting with BGP and I am stuck on this, for some reason, not all routes are been advertised, I don't know what is the trick to do here.  thanks,

R1:

Interface GigabitEthernet0/0
no switchport
ip address 192.168.101.1 255.255.255.252
negotiation auto
router bgp 64550
bgp log-neighbor-changes
neighbor 192.168.101.2 remote-as 64520
neighbor 192.168.101.2 description R2
!
address-family ipv4
  network 192.168.101.0 mask 255.255.255.252
  neighbor 192.168.101.2 activate
exit-address-family

R2

interface GigabitEthernet0/0
ip address 192.168.100.2 255.255.255.252
duplex auto
speed auto
media-type rj45
!
interface GigabitEthernet0/1
ip address 192.168.101.2 255.255.255.0
duplex auto
speed auto
media-type rj45

router bgp 64520
bgp log-neighbor-changes
neighbor 192.168.100.1 remote-as 64550
neighbor 192.168.100.1 description R3
neighbor 192.168.101.1 remote-as 64550
neighbor 192.168.101.1 description R1
!
address-family ipv4
  network 192.168.100.0 mask 255.255.255.252
  network 192.168.101.0 mask 255.255.255.252
  neighbor 192.168.100.1 activate
  neighbor 192.168.101.1 activate
exit-address-family

R3

Interface GigabitEthernet0/0
no switchport
ip address 192.168.100.1 255.255.255.252
negotiation auto

!
router bgp 64550
bgp log-neighbor-changes
neighbor 192.168.100.2 remote-as 64520
neighbor 192.168.100.2 description R2
!
address-family ipv4
  network 192.168.100.0 mask 255.255.255.252
  neighbor 192.168.100.2 activate
exit-address-family

[MHM Cisco World]

Path loop prevent R1 and R3 receive route from same AS.

As M02@rt37 

Allowas-in 

Solution here sure.

[TaimurKhan]

at R2 u can use command under bgp "neighbor 192.168.100.1 as-override " and "neighbor 192.168.101.1 as-override "

or use at R1 and R3 under bgp

"neighbor 192.168.101.2 allowas-in"

"neighbor 192.168.100.2 allowas-in"

[MHM Cisco World]

this not vpnv4 as-override not work here

MHM

[MHM Cisco World · Accepted solution]

It work for my side 
BUT this design have two issue 
1- 
we advertise the LINK between BGP neighbor via BGP, this I dont recommend AT ALL and for any case avoided it 
then how can I test config 
config LO in R1(IOU1 in my lab) and R3(IOU3 in my lab)
advertise these LO and test ping between it 

2-
allowas-in we use this feature in VPNv4 super backbone, but here it make LOOP 
how I know there is LOOP 
if we check show ip bgp 
we see 200.0.0.0 (subnet between IOU2 and IOU3) have two path 
one with next-hop 0.0.0.0 that OK since we advertise this subent via BGP (point1) 
other via IOU2 which I dont run any network command, so from where ? 200.0.0.0 is advertise by IOU1, this LOOP and unpredictable behave.

[MHM Cisco World]

Seriously' dont advertise subnet between two bgp via bgp it make a lot of problems.

There is one link from Cisco about this point I will search when I found it I will send it to you.

Have  a nice summer 

MHM

[Harold Ritter · Accepted solution]

Hi @isabelpgv1 ,

Interface gi0/1 on R2 has the wrong mask. This is causing confusion in BGP. Please fixed it and retry.

interface GigabitEthernet0/1
ip address 192.168.101.2 255.255.255.0

should be 

ip address 192.168.101.2 255.255.255.252

Regards,