MPLS VPN PE-CE OSPF Default Route

When you try to advertise a default route from one CE router to another CE router in an MPLS VPN PE-CE OSPF topology, you might be disappointed that it doesn’t show up on the other end. There are some additional commands we have to add before our PE routers advertise a default route.

In this lesson, I’ll explain how to advertise that default route. I’ll also show you which show commands to use to check your CE and PE routers. Let’s get started!

Configuration

Below is the topology we are going to use:

mpls vpn pe ce ospf gigabit

This is the same topology I used in the MPLS VPN PE-CE OSPF lesson.

  • Configurations
  • CE1
  • CE2
  • P
  • PE1
  • PE2

Want to take a look for yourself? Here you will find the startup configuration of each device.

We advertise a default route on CE1:

CE1(config)#router ospf 1
CE1(config-router)#default-information originate always

This default route doesn’t show up on CE2:

CE2#show ip route ospf

      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/3] via 192.168.45.4, 00:27:34, GigabitEthernet0/1
O IA  192.168.12.0/24 [110/2] via 192.168.45.4, 00:27:34, GigabitEthernet0/1

Let’s find out what is going on. PE1 has it in its routing table:

PE1#show ip route vrf CUSTOMER | include 0.0.0.0/0
O*E2  0.0.0.0/0 [110/1] via 192.168.12.1, 00:10:02, GigabitEthernet0/1

However, it’s not in the BGP table:

PE1#show ip bgp vpnv4 vrf CUSTOMER

     Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf CUSTOMER)
 *>   1.1.1.1/32       192.168.12.1             2         32768 ?
 *>i  5.5.5.5/32       4.4.4.4                  2    100      0 ?
 *>   192.168.12.0     0.0.0.0                  0         32768 ?
 *>i  192.168.45.0     4.4.4.4                  0    100      0 ?

The default route doesn’t show up because, by default, the redistribute ospf BGP command doesn’t redistribute OSPF external routes. Here’s what our configuration looks like on PE1:

PE1#show run | begin router bgp
router bgp 234
 bgp log-neighbor-changes
 neighbor 4.4.4.4 remote-as 234
 neighbor 4.4.4.4 update-source Loopback0
 !
 address-family ipv4
  no neighbor 4.4.4.4 activate
 exit-address-family
 !
 address-family vpnv4
  neighbor 4.4.4.4 activate
  neighbor 4.4.4.4 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf CUSTOMER
  redistribute ospf 2
 exit-address-family

Let’s change the redistribute command so that OSPF external routes are also redistributed into BGP:

PE1(config)#router bgp 234
PE1(config-router)#address-family ipv4 vrf CUSTOMER
PE1(config-router-af)#redistribute ospf 2 match internal external