EIGRP Stub routing is one of the feature of EIGRP routing protocol to improve the stability and reduce resource utilization. EIGRP stub routing is often used in the hub and spoke topology where the eigrp stub is enabled on the spoke routers. Also, EIGRP stub can limit the query when the upstream routers go to Active state searching for the route.
When configuring EIGRP stub, the default value of cisco IOS is "eigrp stub connected summary" which means the stub router will advertise only connected and summary routes to the upstream routers. However, we can change this setting by adding the following option to the eigrp stub.
eigrp stub[receive-only | connected | static |summary]
Example
In this example, we will have 2 scenarios.
Scenario 1:
R1 is configured as a stub router and use the default value which is connected and summary. All of the routers in this scenario are in the EIGRP domain.
Before EIGRP stub enabled on R1, we can see the routing table of R3 that it has route to network 10.1.1.0/24. However, when we configure stub on R1, because 10.1.1.0/24 network is not connected or summary on R1, it will not be advertised to R3. Therefore, after enabling stub command, we do not see 10.1.1.0/24 network on R3
Before enabling eigrp stub on R1
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24 is directly connected, Loopback0
D 1.0.0.0/8 is a summary, 00:14:46, Null0
2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, Loopback1
D 2.0.0.0/8 is a summary, 00:14:46, Null0
D 10.0.0.0/8 [90/435200] via 192.168.1.2, 00:01:25, FastEthernet0/0
C 192.168.1.0/24 is directly connected, FastEthernet0/0
D 192.168.2.0/24 [90/307200] via 192.168.1.2, 00:12:05, FastEthernet0/0
Enabling EIGRP Stub
R1
router eigrp 1
network 0.0.0.0
auto-summary
eigrp stub connected summary
R3 routing table ( no network 10.1.1.0/24 in its routing table )
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24 is directly connected, Loopback0
D 1.0.0.0/8 is a summary, 00:15:44, Null0
2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, Loopback1
D 2.0.0.0/8 is a summary, 00:15:44, Null0
C 192.168.1.0/24 is directly connected, FastEthernet0/0
D 192.168.2.0/24 [90/307200] via 192.168.1.2, 00:00:24, FastEthernet0/0
Scenario 2:
We enable EIGRP stub on R2. However this time, we configured EIGRP stub on R2. but we chose option received-only, which means R2 will not advertise any of its route to R1 (upstream router)
Before configuring EIGRP stub received-only on R2
R1 routing table
R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 1.0.0.0/8 [90/409600] via 192.168.1.1, 00:02:51, FastEthernet0/0
D 2.0.0.0/8 [90/409600] via 192.168.1.1, 00:02:51, FastEthernet0/0
D 10.0.0.0/8 [90/409600] via 192.168.2.2, 00:00:11, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, FastEthernet0/1
After configuring EIGRP stub receive-only on R2
router eigrp 1
network 10.0.0.0
network 192.168.2.0
auto-summary
eigrp stub receive-only
R1 routing table. As expected, we do not have 10.1.1.0/24 in R1 routing table
R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 1.0.0.0/8 [90/409600] via 192.168.1.1, 00:01:08, FastEthernet0/0
D 2.0.0.0/8 [90/409600] via 192.168.1.1, 00:01:08, FastEthernet0/0
C 192.168.1.0/24 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, FastEthernet0/1
No comments:
Post a Comment