Embedded Files
Redistribution between IS-IS and OSPF
Network topology:
Configuration task:
RA router is running OSPF and RC router is running IS-IS. At RB router, all the IS-IS routes are Level 1. Configure mutual redistribution at RB router by using summarization wherever possible. The OSPF routes should be advertised into the IS-IS domain as external routes.
Configuration:
OSPF Configuration on RA
interface fastethernet 0/0 ip address 172.16.1.145 255.255.255.240 ip ospf 1 area 0!router ospf 1 router-id 1.1.1.1!OSPF and ISIS Configuration on RB
interface fastethernet 0/1 ip address 172.16.1.146 255.255.255.240 ip ospf 1 area 0!interface fastethernet 0/0 ip address 172.16.1.97 255.255.255.224 ip router isis!router ospf 1 router-id 2.2.2.2 redistribute connected subnets ! Required to advertise the network connected to RC router. redistribute isis metric 30 level-1 subnets ! This redistributes all ISIS Level-1 routes learnt by RB into OSPF domain!router isis net 49.0001.2222.2222.2222.00 redistribute ospf 1 metric 100 match internal ! This redistributes all OSPF internal (intra and inter-area) routes into ISIS domain!ISIS Configuration on RC
interface fastethernet 0/0 ip address 172.16.1.98 255.255.255.224 ip router isis!router isis net 49.0001.3333.3333.3333.00!Routing tables:
The following output shows OSPF and ISIS routes learned by RB router.
OSPF and ISIS routes
RB# show ip route ospf 172.16.0.0/16 is variably subnetted, 9 subnets, 2 masksO 172.16.1.160/28 [110/65] via 172.16.1.145, 00:06:50, FastEthernet0/1O 172.16.1.128/28 [110/65] via 172.16.1.145, 00:06:50, FastEthernet0/1O 172.16.1.224/28 [110/65] via 172.16.1.145, 00:06:50, FastEthernet0/1O 172.16.1.192/28 [110/65] via 172.16.1.145, 00:06:50, FastEthernet0/1RB# show ip route isis 172.16.0.0/16 is variably subnetted, 9 subnets, 2 masksi L1 172.16.2.128/27 [115/20] via 172.16.1.98, FastEthernet0/0i L1 172.16.2.32/27 [115/20] via 172.16.1.98, FastEthernet0/0i L1 172.16.2.64/27 [115/20] via 172.16.1.98, FastEthernet0/0OSPF External routes on RA
RA# show ip route ospf 172.16.0.0/16 is variably subnetted, 9 subnets, 2 masksO E2 172.16.2.128/27 [110/30] via 172.16.1.146, 00:01:47, FastEthernet0/0O E2 172.16.2.32/27 [110/30] via 172.16.1.146, 00:01:47, FastEthernet0/0O E2 172.16.1.96/27 [110/20] via 172.16.1.146, 00:00:01, FastEthernet0/0O E2 172.16.2.64/27 [110/30] via 172.16.1.146, 00:01:47, FastEthernet0/0ISIS Level-2 routes on RC
The following output shows ISIS External routes learnt by RC router as redistributed by RB router.RC# show ip route isis 172.16.0.0/16 is variably subnetted, 9 subnets, 2 masksi L2 172.16.1.160/28 [115/40] via 172.16.1.97, FastEthernet0/0i L2 172.16.1.144/28 [115/40] via 172.16.1.97, FastEthernet0/0i L2 172.16.1.128/28 [115/40] via 172.16.1.97, FastEthernet0/0i L2 172.16.1.224/28 [115/40] via 172.16.1.97, FastEthernet0/0i L2 172.16.1.192/28 [115/40] via 172.16.1.97, FastEthernet0/0Summarization:
As seen above, the subnetworks 172.16.1.128/28, 172.16.1.144/28, 172.16.1.160/28, 172.16.1.192/28 and 172.16.1.224/28 can be summarised into ISIS domain at RB router with a supernet 172.16.1.128/25 which encompasses all the subnetworks.
Summarization at RB
router isis summary-address 172.16.1.128 255.255.255.128!This causes RB router to advertise only the summarised route to RC router. The RB router also points this summarized route towards Null0 interface so if any packets match to this summarised route, it will be dropped. "su" indicates IS-IS summary route.
RC routing table
RB# show ip route isis 172.16.0.0/16 is variably subnetted, 10 subnets, 3 masksi su 172.16.1.128/25 [115/30] via 0.0.0.0, Null0i L1 172.16.2.128/27 [115/20] via 172.16.1.98, FastEthernet0/0i L1 172.16.2.32/27 [115/20] via 172.16.1.98, FastEthernet0/0i L1 172.16.2.64/27 [115/20] via 172.16.1.98, FastEthernet0/0RC# show ip route isis 172.16.0.0/16 is variably subnetted, 5 subnets, 2 masksi L2 172.16.1.128/25 [115/40] via 172.16.1.97, FastEthernet0/0Page updated
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