KEY CONCEPTS:

   > EIGRP STUB SUMMARY router accepts all the routes advertise by neighboring routers.
   > ONLY the SUMMARIZED Address configured on the STUB Router will be advertised.

MANILA ROUTER EIGRP CONFIGURATIONS:

MANILA#sh run | sec eigrp
router eigrp 12
 network 10.10.1.0 0.0.0.255
 network 10.10.2.0 0.0.0.255
 network 10.10.3.0 0.0.0.255
 network 192.168.12.0

MELBOURNE ROUTER EIGRP CONFIGURATIONS:

MELBOURNE#sh run | sec eigrp
 router eigrp 12
 network 192.168.12.0
 network 192.168.23.0
 network 200.200.200.0

SINGAPORE ROUTER EIGRP CONFIGURATIONS:

SINGAPORE#sh run | sec eigrp
router eigrp 12
 network 150.150.150.0 0.0.0.255
 network 192.168.23.0

I would expect that the Routing Table for each of the three routers are complete as per the network instantiated under EIGRP Process.

MANILA#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      150.150.0.0/24 is subnetted, 1 subnets
D        150.150.150.0 [90/2809856] via 192.168.12.2, 00:00:05, Serial2/0
D     192.168.23.0/24 [90/2681856] via 192.168.12.2, 00:01:46, Serial2/0
D     200.200.200.0/24 [90/2297856] via 192.168.12.2, 00:01:47, Serial2/0

MELBOURNE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/24 is subnetted, 3 subnets
D        10.10.1.0 [90/2297856] via 192.168.12.1, 00:02:16, Serial2/0
D        10.10.2.0 [90/2297856] via 192.168.12.1, 00:02:16, Serial2/0
D        10.10.3.0 [90/2297856] via 192.168.12.1, 00:02:16, Serial2/0
      150.150.0.0/24 is subnetted, 1 subnets
D        150.150.150.0 [90/2297856] via 192.168.23.3, 00:00:34, Serial2/1

SINGAPORE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/24 is subnetted, 3 subnets
D        10.10.1.0 [90/2809856] via 192.168.23.2, 00:02:33, Serial2/1
D        10.10.2.0 [90/2809856] via 192.168.23.2, 00:02:33, Serial2/1
D        10.10.3.0 [90/2809856] via 192.168.23.2, 00:02:33, Serial2/1
D     192.168.12.0/24 [90/2681856] via 192.168.23.2, 00:02:33, Serial2/1
D     200.200.200.0/24 [90/2297856] via 192.168.23.2, 00:02:33, Serial2/1

Let’s configure the “EIGRP STUB SUMMARY ” on MELBOURNE Router.

MELBOURNE#config t
Enter configuration commands, one per line.  End with CNTL/Z.
MELBOURNE(config)#router eigrp 12
MELBOURNE(config-router)#eigrp stub summary

As observed, no routes were received by MANILA Router and SINGAPORE routers.

MANILA#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

MANILA#

SINGAPORE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

SINGAPORE#

For MELBOURNE Router, it still can received network address from both MANILA and SINGAPORE Routers.

MELBOURNE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/24 is subnetted, 3 subnets
D        10.10.1.0 [90/2297856] via 192.168.12.1, 00:00:15, Serial2/0
D        10.10.2.0 [90/2297856] via 192.168.12.1, 00:00:15, Serial2/0
D        10.10.3.0 [90/2297856] via 192.168.12.1, 00:00:15, Serial2/0
      150.150.0.0/24 is subnetted, 1 subnets
D        150.150.150.0 [90/2297856] via 192.168.23.3, 00:00:15, Serial2/1

NOW, Lets summarized the network addresses advertise by MANILA Router on the MELBOURNE Router so that It will only advertised summary routes to SINGAPORE.

MELBOURNE(config-if)#int s2/1
MELBOURNE(config-if)#ip summary-address eigrp 12 10.0.0.0 255.0.0.0
MELBOURNE(config-if)#


So what does the MELBOURNE Routing Table shows about the summary address.

MELBOURNE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
D        10.0.0.0/8 is a summary, 00:02:22, Null0
D        10.10.1.0/24 [90/2297856] via 192.168.12.1, 00:12:44, Serial2/0
D        10.10.2.0/24 [90/2297856] via 192.168.12.1, 00:12:44, Serial2/0
D        10.10.3.0/24 [90/2297856] via 192.168.12.1, 00:12:44, Serial2/0
      150.150.0.0/24 is subnetted, 1 subnets
D        150.150.150.0 [90/2297856] via 192.168.23.3, 00:12:44, Serial2/1

>> As observed, the summary address were set to Null.

Let’s check the Routing Table of SINGAPORE Router.

SINGAPORE#sh ip route eigrp
Codes: L – local, 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

D     10.0.0.0/8 [90/2809856] via 192.168.23.2, 00:00:05, Serial2/1

>> As observed above, we can ONLY see that the summarized address on SINGAPORE Router Routing Table.