Route Summarization
Route summarization makes the routing table smaller, but still allows complete IP connectivity, if everything is configured properly.
The following example consists of a three-router topology, in which R2 is doing the summarization. In this example, R1 is the L1 router, R2 is the L1/L2 router doing the summarization, and R3 is the L2 router. The following configuration is given only for R2, assuming that the adjacencies with R1 and R3 are already up, and the route tables with the appropriate routes are already populated.
Topology
Figure 13-109: Route Summarization Topology
Configuration
R1
#configure terminal | Enter configure mode. |
(config)#router isis 1 | Create an IS-IS routing instance (1). |
(config-router)#net 49.0001.0000.0000.0001.00 | Define the NET address. |
(config-router)#is-type level-1 | Configure instance as level-1. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#interface eth1 | Specify the interface (eth1)to configure and enter Interface mode. |
(config-if)#ip address 20.20.20.1/24 | Configure IP address on interface. |
(config-if)#isis circuit-type level-1 | Set the circuit type as level-1 for the interface |
(config-if)#ip router isis 1 | Enable IS-IS routing on interface eth1 (connected to R2). |
(config-if)#commit | Commit candidate configuration to the running configuration |
R2
#configure terminal | Enter configure mode. |
(config)#interface eth1 | Specify the interface (eth1)to configure and enter Interface mode. |
(config-if)#isis circuit-type level-1 | Set the circuit type as level-1 for the interface |
(config-if)#ip address 20.20.20.2/24 | Configure IP address on interface. |
(config-if)#ip router isis 1 | Enable IS-IS routing on interface eth1 (connected to R1). |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode and return to Configure mode. |
(config)#interface eth2 | Specify the interface (eth2)to configure and enter Interface mode. |
(config-if)#ip address 30.30.30.1/24 | Configure IP address on interface. |
(config-if)#isis circuit-type level-2-only | Set the circuit type as level-2-only for the interface |
(config-if)#ip router isis 1 | Enable IS-IS routing on interface eth2 (connected to R3). |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode and return to Configure mode. |
(config)#router isis 1 | Create an IS-IS routing instance (1). |
(config-router)#net 49.0001.0000.0000.0002.00 | Define the NET address. |
(config-router-af)#redistribute isis level-2 into level-1 | Enable redistribution of isis routes from level-2 into level-1 |
(config-router-af)# summary-address 66.66.66.0/24 level-1 metric 50 | Configure the summary address to summarize IP reachability information. |
(config-if)#commit | Commit candidate configuration to the running configuration |
R3
#configure terminal | Enter configure mode. |
(config)#ip route 66.66.66.1/32 eth2 | Configure ip static route. |
(config)#ip route 66.66.66.2/32 eth2 | Configure ip static route. |
(config)#ip route 66.66.66.3/32 eth2 | Configure ip static route. |
(config)#router isis 1 | Create an IS-IS routing instance (1). |
(config-router)#is-type level-2-only | Configure instance as level-2-only routing. |
(config-router)#net 49.0001.0000.0000.0003.00 | Define the NET address. |
(config-router)#redistribute static | Enable redistribution of static routes into ISIS instance. |
(config-if)#commit | Commit candidate configuration to the running configuration |
(config-router)#exit | Exit router mode. |
(config)#interface eth2 | Specify the interface (eth2)to configure and enter Interface mode. |
(config-if)#ip address 30.30.30.2/24 | Configure IP address on interface. |
(config-if)#isis circuit-type level-2-only | Set the circuit type as level-2-only for the interface |
(config-if)#ip router isis 1 | Enable IS-IS routing on interface eth1 (connected to R2). |
(config-if)#commit | Commit candidate configuration to the running configuration |
Validation
R1#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 0
Total number of adjacencies: 1
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth1 5254.002a.230a Up 20 L1 IS-IS
R2#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 1
Total number of adjacencies: 2
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.00dc.0b76 Up 6 L1 IS-IS
0000.0000.0003 eth2 5254.00a8.940d Up 7 L2 IS-IS
R3#show clns neighbors
Total number of L1 adjacencies: 0
Total number of L2 adjacencies: 1
Total number of adjacencies: 1
Tag 1: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth2 5254.007e.5ade Up 21 L2 IS-IS
R1#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag 1: VRF : default
Destination Metric Next-Hop Interface Tag
C 20.20.20.0/24 10 -- eth1 0
ia 30.30.30.0/24 20 20.20.20.2 eth1 0
ia 66.66.66.0/24 60 20.20.20.2 eth1 0
R2#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag 1: VRF : default
Destination Metric Next-Hop Interface Tag
C 20.20.20.0/24 10 -- eth1 0
C 30.30.30.0/24 10 -- eth2 0
D 66.66.66.0/24 0 -- --
L2 66.66.66.1/32 10 30.30.30.2 eth2 0
L2 66.66.66.2/32 10 30.30.30.2 eth2 0
L2 66.66.66.3/32 10 30.30.30.2 eth2 0
R3#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** - invalid
Tag 1: VRF : default
Destination Metric Next-Hop Interface Tag
L2 20.20.20.0/24 20 30.30.30.1 eth2 0
C 30.30.30.0/24 10 -- eth2 0
E 66.66.66.1/32 0 -- -- 0
E 66.66.66.2/32 0 -- -- 0
E 66.66.66.3/32 0 -- -- 0
R1#show isis database verbose
Tag 1: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00* 0x00000004 0xF4AD 850 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 20.20.20.1
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IP 20.20.20.0 255.255.255.0
0000.0000.0001.01-00* 0x00000003 0x1BBF 850 0/0/0
Metric: 0 IS 0000.0000.0001.00
Metric: 0 IS 0000.0000.0002.00
0000.0000.0002.00-00 0x00000010 0xB5E0 1165 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 20.20.20.2
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IP 20.20.20.0 255.255.255.0
Metric: 10 IP-Interarea 30.30.30.0 255.255.255.0
Metric: 50 IP-External 66.66.66.0 255.255.255.0
R2#show isis database verbose
Tag 1: VRF : default
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00 0x00000004 0xF4AD 820 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 20.20.20.1
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IP 20.20.20.0 255.255.255.0
0000.0000.0001.01-00 0x00000003 0x1BBF 820 0/0/0
Metric: 0 IS 0000.0000.0001.00
Metric: 0 IS 0000.0000.0002.00
0000.0000.0002.00-00* 0x00000010 0xB5E0 1137 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 20.20.20.2
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IP 20.20.20.0 255.255.255.0
Metric: 10 IP-Interarea 30.30.30.0 255.255.255.0
Metric: 50 IP-External 66.66.66.0 255.255.255.0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0002.00-00* 0x00000005 0x1577 838 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 30.30.30.1
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IP 30.30.30.0 255.255.255.0
Metric: 10 IP 20.20.20.0 255.255.255.0
0000.0000.0003.00-00 0x0000000B 0xFED3 1160 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 30.30.30.2
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IP 30.30.30.0 255.255.255.0
Metric: 0 IP-External 66.66.66.1 255.255.255.255
Metric: 0 IP-External 66.66.66.2 255.255.255.255
Metric: 0 IP-External 66.66.66.3 255.255.255.255
0000.0000.0003.01-00 0x00000003 0x29AB 837 0/0/0
Metric: 0 IS 0000.0000.0003.00
Metric: 0 IS 0000.0000.0002.00
R3#show isis database verbose
Tag 1: VRF : default
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0002.00-00 0x00000005 0x1577 818 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 30.30.30.1
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IP 30.30.30.0 255.255.255.0
Metric: 10 IP 20.20.20.0 255.255.255.0
0000.0000.0003.00-00* 0x0000000B 0xFED3 1142 0/0/0
Area Address: 49.0001
NLPID: 0xCC
IP Address: 30.30.30.2
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IP 30.30.30.0 255.255.255.0
Metric: 0 IP-External 66.66.66.1 255.255.255.255
Metric: 0 IP-External 66.66.66.2 255.255.255.255
Metric: 0 IP-External 66.66.66.3 255.255.255.255
0000.0000.0003.01-00* 0x00000003 0x29AB 819 0/0/0
Metric: 0 IS 0000.0000.0003.00
Metric: 0 IS 0000.0000.0002.00
Last modified date: 10/16/2023