OSPF Route Tag Configuration example [GNS3 Lab]

Topology:

R1 configuration:

interface Loopback0
 ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
 ip address 10.20.0.1 255.255.255.252
 ip ospf 10 area 0
 duplex full
!
router ospf 10
 router-id 1.1.1.1
!

R2 configuration:


interface FastEthernet0/0
 ip address 10.10.0.1 255.255.255.252
 speed auto
 duplex auto
!
interface FastEthernet0/1
 ip address 10.20.0.2 255.255.255.252
 ip ospf 10 area 0
 speed auto
 duplex auto
!
router ospf 10
 router-id 2.2.2.2
 redistribute connected
 redistribute bgp 65545 subnets route-map BGP_to_OSPF
!
router bgp 65545
 bgp log-neighbor-changes
 bgp redistribute-internal
 neighbor 10.10.0.2 remote-as 65545
!
ip prefix-list BGP_To_OSPF seq 5 permit 3.3.3.3/32
ip prefix-list BGP_To_OSPF seq 15 permit 4.4.4.4/32
!
route-map BGP_to_OSPF permit 10
 match ip address prefix-list BGP_To_OSPF
 set tag 10

R3 configuration:

interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface Loopback1
 ip address 4.4.4.4 255.255.255.255
!
interface FastEthernet0/0
 ip address 10.10.0.2 255.255.255.252
 duplex full
!
router bgp 65545
 bgp log-neighbor-changes
 network 3.3.3.3 mask 255.255.255.255
 network 4.4.4.4 mask 255.255.255.255
 neighbor 10.10.0.1 remote-as 65545

Verification on R1:

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
C        1.1.1.1 is directly connected, Loopback0
      3.0.0.0/32 is subnetted, 1 subnets
O E2     3.3.3.3 [110/1] via 10.20.0.2, 00:17:24, FastEthernet0/0
      4.0.0.0/32 is subnetted, 1 subnets
O E2     4.4.4.4 [110/1] via 10.20.0.2, 00:17:24, FastEthernet0/0
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        10.20.0.0/30 is directly connected, FastEthernet0/0
L        10.20.0.1/32 is directly connected, FastEthernet0/0

We can see the tag when specifying the route:

R1#show ip route  3.3.3.3
Routing entry for 3.3.3.3/32
  Known via "ospf 10", distance 110, metric 1
  Tag 10, type extern 2, forward metric 1
  Last update from 10.20.0.2 on FastEthernet0/0, 00:17:48 ago
  Routing Descriptor Blocks:
  * 10.20.0.2, from 2.2.2.2, 00:17:48 ago, via FastEthernet0/0
      Route metric is 1, traffic share count is 1
      Route tag 10


R1#show ip route  4.4.4.4
Routing entry for 4.4.4.4/32
  Known via "ospf 10", distance 110, metric 1
  Tag 10, type extern 2, forward metric 1
  Last update from 10.20.0.2 on FastEthernet0/0, 00:17:54 ago
  Routing Descriptor Blocks:
  * 10.20.0.2, from 2.2.2.2, 00:17:54 ago, via FastEthernet0/0
      Route metric is 1, traffic share count is 1
      Route tag 10