BGP INTER-AS Option B Configuration and troubleshooting on Huawei routers

Last time I published an article on how to configure BGP Inter-AS Option A. You can check out the article from this link Option A Configuration on Huawei

Let's move a step further and explore how to configure BGP inter-AS option B on Huawei routers.

Quick facts about Inter-AS Option B:

1. It's more scalable and easy to configure compared to option A.
2. Route Targets (RTs) are globally significant.
3. MPLS runs between the ASBRs.
4. We configure VPNV4 peering between ASBRs.
5. NO VRF configurations on the ASBRs, VRFs are only configured on the PEs.
6. ASBRs accepts all the VPNv4 routing information without the VPN target filtering. You need to disable VPN target filtering

Topology

Configuration Procedure

1. Configure IP addresses on interfaces on each router, Configure IGP(ISIS for our case), MPLS, and LDP on all interfaces within the AS. The configuration is the same as option A and is not given here. Let's verify our IGP and MPLS sessions are established by checking their status on the P router in each AS.

1. Configure the VPN instance on PEs and bind the interfaces connecting to the customer to the VPN instance. Pay attention to route targets.

*************************************PE01************************
ip vpn-instance VRF1
 ipv4-family
  route-distinguisher 200:1
  vpn-target 200:1 export-extcommunity
  vpn-target 200:1 import-extcommunity
#
interface GigabitEthernet0/0/0
 ip binding vpn-instance VRF1
 ip address 10.10.10.2 255.255.255.254
#
***********************************PE02****************************
ip vpn-instance VRF1
 ipv4-family
  route-distinguisher 65000:1
  vpn-target 200:1 export-extcommunity
  vpn-target 200:1 import-extcommunity
#
interface GigabitEthernet0/0/1
 ip binding vpn-instance VRF1
 ip address 20.20.20.2 255.255.255.254
#        

1. BGP Configurations for backbone: Configure IBGP VPNV4 peering between PEs and ASBRs. Configure EBGP VPNV4 between ASBRs. Note: You must disable VPN target filtering on both ASBRs.

*******************************PE01**********************************
bgp 200
 router-id 4.4.4.4
 peer 4.4.4.4 as-number 200
 peer 4.4.4.4 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo synchronization
  undo peer 4.4.4.4 enable
 #
 ipv4-family vpnv4
  undo policy vpn-target
  peer 4.4.4.4 enable
 #
********************************ASBR01********************************
bgp 200
 peer 2.2.2.2 as-number 200
 peer 172.16.16.2 as-number 100
 #
 ipv4-family unicast
  undo synchronization
  undo peer 2.2.2.2 enable
  undo peer 172.16.16.2 enable
 #
 ipv4-family vpnv4
  undo policy vpn-target
  peer 2.2.2.2 enable
  peer 172.16.16.2 enable
#        

1. Configure PE-CE routing. BGP is recommended for PE-CE routing protocol.

************************************PE01*******************************
bgp 200
 ipv4-family vpn-instance VRF1
  network 50.50.50.50 255.255.255.255
 #
***********************************Customer01***************************
bgp 65500
 router-id 1.1.1.1
 peer 10.10.10.2 as-number 200
 #
 ipv4-family unicast
  undo synchronization
  network 1.1.1.1 255.255.255.255
  import-route direct
  peer 10.10.10.2 enable
#        

1. Verification

This is how simple it is to set up Inter-AS BGP Option B. The lab setup and all the configurations are available on demand. Ping me if you are interested in trying it out.