RT4 and RT5 redistribute their directly connected network 192.168.1.0/24 into the OSPF routing domain as External Type-2 (E2) route. RT1 selects the path via RT3 instead of RT2 as the forward metric to the E2 route is 2 (the metric between RT1-RT3 and RT3-RT5 links is 1). Forward metric is the cost to reach an ASBR. Note that RT2 also selects the path via RT1-RT3 as it has a lower forward metric to reach RT5, the nearest ASBR in the OSPF routing domain.
Below shows the routing table and OSPF LSDB on RT1:
RT1#sh ip route Gateway of last resort is not set 35.0.0.0/24 is subnetted, 1 subnets O 35.35.35.0 [110/2] via 13.13.13.3, 00:00:36, FastEthernet1/0 24.0.0.0/24 is subnetted, 1 subnets O 24.24.24.0 [110/65] via 12.12.12.2, 00:00:36, FastEthernet0/0 12.0.0.0/24 is subnetted, 1 subnets C 12.12.12.0 is directly connected, FastEthernet0/0 O E2 192.168.1.0/24 [110/20] via 13.13.13.3, 00:00:36, FastEthernet1/0 13.0.0.0/24 is subnetted, 1 subnets C 13.13.13.0 is directly connected, FastEthernet1/0 RT1# RT1#sh ip ospf database --- output omitted --- Type-5 AS External Link States Link ID ADV Router Age Seq# Checksum Tag 192.168.1.0 4.4.4.4 91 0x80000001 0x00B273 0 192.168.1.0 5.5.5.5 91 0x80000001 0x00948D 0 RT1# RT1#sh ip route 192.168.1.1 Routing entry for 192.168.1.0/24 Known via "ospf 100", distance 110, metric 20, type extern 2, forward metric 2 Last update from 13.13.13.3 on FastEthernet1/0, 00:00:36 ago Routing Descriptor Blocks: * 13.13.13.3, from 5.5.5.5, 00:00:36 ago, via FastEthernet1/0 Route metric is 20, traffic share count is 1 RT1#
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