IS-IS and OSPF Redistribution Environment

Figure 12.5 shows an IS-IS and OSPF routing environment. Router A2 is running IS-IS, and routers B1 and B2 are running OSPF. A1 is running both IS-IS and OSPF and is redistributing between the two protocols.

Figure 12.5: Routing scenario amongst IS-IS and OSPF protocols.

Table 12.5: Router Configuration

Router	Relevant Part of Configuration
A1	interface Serial0
	ip address 10.10.1.2 255.255.255.252
	ip router isis
	!
	interface Serial1
	ip address 10.10.2.2 255.255.255.252
	ip router isis
	!
	interface Serial2
	ip address 10.10.3.2 255.255.255.252
	ip router isis
	!
	router ospf 1
	network 10.10.1.0 0.0.0.255 area 0
	network 10.10.2.0 0.0.0.255 area 0
	network 10.10.3.0 0.0.0.255 area 0
	passive-interface Serial0
	redistribute isis route-map redis1
	!
	router isis
	net 25.0001.0000.0000.000a.00
	redistribute ospf 1 metric 30
	!
	route-map redis1 permit 10
	match ip address 20
	set metric 100
	!
	access-list 20 permit 10.10.0.0 0.0.0.255
	access-list 20 permit 192.168.0.0 0.0.248.255
	!
A2	interface Serial0
	ip address 10.10.1.1 255.255.255.252
	ip router isis
	!
	interface Ethernet1
	ip address 192.168.15.1 255.255.255.0
	ip router isis
	!
	router isis
	net 25.0001.0000.0000.000a.00
B1	interface Serial0
	ip address 10.10.2.1 255.255.255.252
	!
	interface Ethernet1
	ip address 192.168.20.1 255.255.255.0
	!
	router ospf 1
	network 10.10.2.0 0.0.0.255 area 0
	network 192.168.20.0 0.0.0.255 area 0
	!
B2	interface Serial0
	ip address 10.10.3.1 255.255.255.252
	!
	interface Ethernet1
	ip address 192.168.30.1 255.255.255.0
	!
	router ospf 1
	network 10.10.3.0 0.0.0.255 area 0
	network 192.168.30.0 0.0.0.255 area 0
	!

In Figure 12.5, the network mail server in the IS-IS routing domain with IP address 192.168.15.2 is inaccessible from Sales LAN 192.168.30.0/24. To troubleshoot this problem:

1. Check the basic IP connectivity by using the ping command at B2. The output of the command is shown in Listing 12.16.

   Listing 12.16 Output of Ping Command

   B2#ping 192.168.15.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.15.2, timeout is 2 seconds: ..... Success rate is 0 percent (0/5)

   In Listing 12.16, there is no Layer-3 connectivity existing between the mail server network and the Sales LAN.

2. Check the presence of the route at B2 by using the command:

   #show ip route 192.168.15.0 % Network not in table

   The command output confirms the unavailability of the route in the OSPF domain.

3. Check if any route is available at A1 by using the command:

   A1#show ip route | inc 192.168.15.0  i  92.168.15.0/24 [115/1] via 10.10.1.1, 00:00:16, Serial0

   The command output shows the presence of an IS-IS route with a next hop of 10.10.1.1. Route 192.168.15.0/24 is available in the IS-IS domain but is unavailable in the OSPF domain. This confirms that there is some problem in redistribution.

4. Obtain the relevant part of the configuration at A1 by issuing the command show running-config, as shown in Listing 12.17.

   Listing 12.17 Output of the show running-config Command

   router ospf 1 network 10.10.1.0 0.0.0.255 area 0 network 10.10.2.0 0.0.0.255 area 0 network 10.10.3.0 0.0.0.255 area 0 passive-interface Serial0 redistribute isis route-map redis1 ! route-map redis1 permit 10 match ip address 20 set metric 100 ! access-list 20 permit 10.10.0.0 0.0.0.255 access-list 20 permit 192.168.0.0 0.0.248.255 !

Listing 12.17 shows that a route map redis1 is used to restrict redistribution from IS-IS to RIP. Only the routes matching access list 20 are redistributed. Network 192.168.15.0/24 does not match access list 20. This causes the nonredistribution of

the route into OSPF. Access list 20 can be suitably modified as shown in Listing 12.18.

Listing 12.18 Modifying Access List 20

A1(config)#no access-list 20 A1(config)access-list 20 permit 10.10.0.0 0.0.0.255 A1(config)access-list 20 permit 192.168.0.0 0.0.240.255