In this scenario, you integrate the IS-IS network you configured in Scenario 4-3 with an OSPF network. Figure 4-7 displays the OSPF network and IS-IS. Router R1 has loopbacks ranging from 131.108.2.0 to 131.108.15.255.
Figure 4-7. OSPF and Integrated IS-IS Network Topology
Because R4 is within both the OSPF and IS-IS domain, you can configure redistribution between OSPF and IS-IS.
To configure redistribution between any IP routing protocols, you must configure a metric that is used within the IP dynamic routing protocol. For OSPF, you must define a cost metric, for example.
Example 4-46 displays the configuration of OSPF redistribution from OSPF to IS-IS on R4 and the step-by-step process required to ensure that all the OSPF routes are advertised as IS-IS routes in the IS-IS domain. The ? tool is used to bring up the available options.
Example 4-46 Routing OSPF to IS-IS on R4
R4(config)#router isis
R4(config-router)#redistribute ?
bgp Border Gateway Protocol (BGP) connected Connected
egp Exterior Gateway Protocol (EGP)
eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) igrp Interior Gateway Routing Protocol (IGRP)
isis ISO IS-IS
iso-igrp IGRP for OSI networks level-1 IS-IS level-1 routes only
level-1-2 IS-IS level-1 and level-2 routes level-2 IS-IS level-2 routes only
metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes mobile Mobile routes
odr On Demand stub Routes
ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) route-map Route map reference
static Static routes <cr>
R4(config-router)#redistribute ospf ? <1-65535> Process ID
R4(config-router)#redistribute ospf 1 ? level-1 IS-IS level-1 routes only
level-1-2 IS-IS level-1 and level-2 routes level-2 IS-IS level-2 routes only
match Redistribution of OSPF routes metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference
vrf VPN Routing/Forwarding Instance <cr>
R4(config-router)#redistribute ospf 1 level-2 ? match Redistribution of OSPF routes metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference
<cr>
R4(config-router)#redistribute ospf 1 level-2 metric ? <0-63> ISIS default metric
R4(config-router)#redistribute ospf 1 level-2 metric 10
When redistributing from OSPF to IS-IS, you need to define the OSPF process ID from which the OSPF routes will be injected. The OSPF process ID is 1.
Because OSPF uses cost as the metric for making routing decisions and IS-IS uses L1 or L2, you must define the IS-IS router type. (The router type along with IS-IS metric is between 0–63.)
Three options are available when you are redistributing from OSPF to IS-IS: L1, L2, and L1/2.
In this scenario, you configure L2 routes. Finally, you need to define an IS-IS metric;
the chosen value of 10 is used. Any value between 0 and 63 is a valid metric.
View the IP routing table inside in IS-IS network. Example 4-47 displays the IP routing table on R8.
Example 4-47 R8's IP Routing Table
R8#show ip route
Codes: C - connected, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level- 2, ia - IS-IS
inter area
141.108.0.0/16 is variably subnetted, 6 subnets, 2 masks
C 141.108.255.8/30 is directly connected, Serial1 C 141.108.255.4/30 is directly connected, Serial0 i L1 141.108.255.0/30 [115/20] via 141.108.255.9, Serial1 C 141.108.3.0/24 is directly connected, Ethernet0 i L1 141.108.2.0/24 [115/30] via 141.108.255.9, Serial1 i L1 141.108.4.0/24 [115/20] via 141.108.255.9, Serial1 131.108.0.0/24 is subnetted, 15 subnets
i L2 131.108.254.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.15.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.14.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.13.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.12.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.11.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.10.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.9.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.8.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.7.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.6.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.5.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.4.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.3.0 [115/30] via 141.108.255.9, Serial1 i L2 131.108.2.0 [115/30] via 141.108.255.9, Serial1
Example 4-47 displays the remote OSPF routes redistributed from the OSPF
backbone on R1 into IS-IS as L2 routes, and a metric of 30, which comes from the addition of the 10 used in redistribution and the two hop counts between R4 to R9 and R9 to R8. Try to ping the remote address. Example 4-48 displays a sample ping request from R8 to the L2 IS-IS route 131.108.2.1 (R2's loopback address).
Example 4-48 Sample Ping Request to 131.108.2.1 from R8
R8#ping 131.108.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.2.1, timeout is 2 seconds:
...
Success rate is 0 percent (0/5) R8#
The ping request receives no replies. R8 has a routing entry for this network. The reason the ping request receives no replies is because R8 sends the request to the next hop address of 141.108.255.9 (R9) and R9 sends the request to R4. Example 4- 49 displays R9's IP routing table confirming the next hop address.
Example 4-49 IP Routing Table on R9
R9#sh ip route
Codes: C - connected, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level- 2, * - candidate
default
141.108.0.0/16 is variably subnetted, 6 subnets, 2 masks C 141.108.255.8/30 is directly connected, Serial1
i L1 141.108.255.4/30 [115/50] via 141.108.255.1, Serial0 [115/50] via 141.108.255.10, Serial1
C 141.108.255.0/30 is directly connected, Serial0 i L1 141.108.3.0/24 [115/20] via 141.108.255.10, Serial1 i L1 141.108.2.0/24 [115/20] via 141.108.255.1, Serial0 C 141.108.4.0/24 is directly connected, Ethernet0 131.108.0.0/24 is subnetted, 15 subnets
i L2 131.108.254.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.15.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.14.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.13.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.12.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.11.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.10.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.9.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.8.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.7.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.6.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.5.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.4.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.3.0 [115/20] via 141.108.255.1, Serial0 i L2 131.108.2.0 [115/20] via 141.108.255.1, Serial0
Example 4-49 displays the next hop address of 141.108.255.1 (R4). Now, R4 can ping the remote address as confirmed by Example 4-50.
Example 4-50 Sample Ping from R4 to 131.108.2.1
R4>ping 131.108.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms R4>
The last hop you need to look at is R1. Example 4-51 displays R1's OSPF routing table. Remember that R1 is configured for OSPF only.
Example 4-51 R1's OSPF Routing Table
R1#sh ip route ospf R1#
NOTE
R4's routing table contains all the OSPF network entries advertised by R1, and because R1 and R4 are maintaining a full OSPF adjacency and the next hop address is a directly connected LAN, ping requests are replied to when R4 pings the address 131.108.2.1.
The reason that R1 has no remote OSPF entries and hence has no return path to the remote routers R8 or R9 in the IS-IS domain is that you have not redistributed from IS-IS to OSPF. So far you have only configured one-way redistribution; you must also advise the OSPF domain of the IS-IS routes. Once more, configure redistribution
on R4, but this time, configure IS-IS to OSPF redistribution. Example 4-52 displays the configuration options when redistributing from IS-IS to OSPF.
Example 4-52 Configuring IS-IS to OSPF Redistribution
R4(config)#router ospf 1
R4(config-router)#redistribute isis ? level-1 IS-IS level-1 routes only
level-1-2 IS-IS level-1 and level-2 routes level-2 IS-IS level-2 routes only
metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference
subnets Consider subnets for redistribution into OSPF tag Set tag for routes redistributed into OSPF <cr>
WORD ISO routing area tag
R4(config-router)#redistribute isis level-1-2 ? metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference
subnets Consider subnets for redistribution into OSPF tag Set tag for routes redistributed into OSPF <cr>
R4(config-router)#redistribute isis level-1-2 metric 100 ? metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference
subnets Consider subnets for redistribution into OSPF tag Set tag for routes redistributed into OSPF <cr>
R4(config-router)#redistribute isis level-2 metric 100 metric?
metric metric-type
R4(config-router)#redistribute isis level-2 metric 100 metric-type ? 1 Set OSPF External Type 1 metrics
2 Set OSPF External Type 2 metrics
R4(config-router)#redistribute isis level-1-2 metric 100 metric-type 1 subnets
NOTE
The keyword subnets is required here because 141.108.0.0 is subnetted using a Class C address, which is required whenever redistribution is configured to a classless domain and a 30-bit mask on serial connections.
Now, view R1's IP routing table. Example 4-53 displays R1's OSPF routing table.
Example 4-53 R1's OSPF Routing Table
R1>sh ip route ospf
141.108.0.0/16 is variably subnetted, 3 subnets, 2 masks O E2 141.108.255.8/30 [110/100] via 131.108.254.2, 00:00:00, Ethernet0/0
O E2 141.108.3.0/24 [110/100] via 131.108.254.2, 00:00:00, Ethernet0/0
O E2 141.108.4.0/24 [110/100] via 131.108.254.2, 00:00:00, Ethernet0/0
Three remote networks are present, but none of the directly connected links on R4 are present. You also need to redistribute any locally connected routers on R4.
Configure this and use type 1 OSPF routes this time. Example 4-54 displays the configuration of locally connected routes to be injected into IS-IS on R4.
Example 4-54 Redistribute Connected on R4
R4(config-router)#router ospf 1
R4(config-router)# redistribute connected subnets metric 100 metric- type 1
Example 4-55 now displays the full IP network present in the IS-IS domain.
Example 4-55 show ip route ospf Command on R1
R1>sh ip route ospf
141.108.0.0/16 is variably subnetted, 6 subnets, 2 masks O E2 141.108.255.8/30 [110/100] via 131.108.254.2, 00:07:39, Ethernet0/0
O E2 141.108.3.0/24 [110/100] via 131.108.254.2, 00:07:39, Ethernet0/0
O E2 141.108.4.0/24 [110/100] via 131.108.254.2, 00:07:39, Ethernet0/0
O E1 141.108.2.0/24 [110/110] via 131.108.254.2, 00:07:29, Ethernet0/0
O E1 141.108.255.4/30 [110/110] via 131.108.254.2, 00:07:29, Ethernet0/0
O E1 141.108.255.0/30 [110/110] via 131.108.254.2, 00:07:29, Ethernet0/0
You have seen the power of the command redistribute. By simply using keywords, you can redistribute routes with the appropriate metric and route type (1 or 2 in OSPF or L1/L2 in IS-IS). You can now provide connectivity between the two different routing domains. Confirm connectivity by pinging from R8 to R1 loopback addresses 131.108.2.1/24 through 131.108.10.1/24, as displayed in Example 4-56.
Example 4-56 Sample Pings from R8 to R1
R8#ping 131.108.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.3.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.3.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.4.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.4.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.5.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.5.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.6.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.6.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.7.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.7.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/18/20 ms R8#ping 131.108.8.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.8.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/18/20 ms R8#ping 131.108.9.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.9.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms R8#ping 131.108.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 131.108.10.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/18/20 ms R8#
A sample trace from R9 to R1 displays the route path taken to the network 131.108.2.1/24, as displayed in Example 4-57.
Example 4-57 Trace Route to 131.108.2.1 from R9
R9#trace 131.108.2.1
Type escape sequence to abort.
Tracing the route to 131.108.2.1
1 141.108.255.1 8 msec 8 msec 12 msec 2 131.108.254.1 12 msec 8 msec *
Assume the link between R9 and R4 fails, so the only path to the OSPF backbone is through R8. Example 4-58 displays a sample trace when the primary path fails.
Example 4-58 Trace on R9 Through R8
R9# trace 131.108.2.1
Type escape sequence to abort.
Tracing the route to 131.108.2.1
1 141.108.255.10 8 msec 8 msec 12 msec
2 141.108.255.6 20 msec 16 msec 16 msec 3 131.108.254.1 16 msec 16 msec *
The new IP routing table on R9 contains a path to all OSPF routes through the Serial connection to R8. Example 4-59 displays R9's IS-IS routing table when the link failure to R4 occurs.
Example 4-59 show ip route isis Command on R9
R9#sh ip route isis
141.108.0.0/16 is variably subnetted, 5 subnets, 2 masks i L1 141.108.255.4/30 [115/20] via 141.108.255.10, Serial1 i L1 141.108.3.0/24 [115/20] via 141.108.255.10, Serial1 i L1 141.108.2.0/24 [115/30] via 141.108.255.10, Serial1 131.108.0.0/24 is subnetted, 15 subnets
i L2 131.108.254.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.15.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.14.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.13.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.12.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.11.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.10.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.9.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.8.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.7.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.6.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.5.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.4.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.3.0 [115/158] via 141.108.255.10, Serial1 i L2 131.108.2.0 [115/158] via 141.108.255.10, Serial1