Last time we looked at how to configure Inter-AS BGP MPLS Option-A. You can check out the article from this link: INTER-AS BGP MPLS OPTION A. In this article, we will simulate how to configure INTER-AS BGP MPLS 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 Setup

Configuration Steps:

Step 1: Basic Configuration

Configure IP addresses on interfaces on each router, Configure IGP(ISIS for our case), MPLS, and LDP on all interfaces within the AS. Refer to this article for IS-IS Configurations, Configuring ISIS on Huawei. Below is sample IS-IS and interface configuration for PE01:

*******************************PE01
sys
isis 20
 is-level level-2
 cost-style wide
 network-entity 49.0000.0020.0200.2002.00
 is-name PE01
#
interface GigabitEthernet0/0/1
 ip address 10.251.250.3 255.255.255.254
 isis enable 20
 isis circuit-type p2p
 isis cost 100
 mpls
 mpls ldp
#

Let’s verify our IGP and MPLS sessions are established by checking their status on the P router in each AS using the commad display isis peer

Step 2: 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
#

*******************************ASBR02*********************************
#
bgp 100
 peer 7.7.7.7 as-number 100
 peer 7.7.7.7 connect-interface LoopBack0
 peer 172.16.16.3 as-number 200
 #
 ipv4-family unicast
  undo synchronization
  undo peer 7.7.7.7 enable
  undo peer 172.16.16.3 enable
 #
 ipv4-family vpnv4
  undo policy vpn-target
  peer 7.7.7.7 enable
  peer 172.16.16.3 enable
#

******************************PE02*****************************************
#
bgp 100
 peer 5.5.5.5 as-number 100
 peer 5.5.5.5 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo synchronization
  peer 5.5.5.5 enable
 #
 ipv4-family vpnv4
  undo policy vpn-target
  peer 5.5.5.5 enable
 #
 ipv4-family vpn-instance VRF1
  peer 20.20.20.3 as-number 65000
#

Step 3: Configure 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
#

Step 4: 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

  import-route direct
  peer 10.10.10.2 enable
#

***************************PE02
 ipv4-family vpn-instance VRF1
  peer 20.20.20.3 as-number 65000
#

***************************Customer2
bgp 65000
 peer 20.20.20.2 as-number 100
 #
 ipv4-family unicast
  undo synchronization

  import-route direct
  peer 20.20.20.2 enable
#

Step 5: Verification.