EIGRP, route summary - GNS3

we gonna use previous network layout and setting

click here to see previous setup

add more loopback on R2


interface Loopback21
 ip address 200.1.2.2 255.255.0.0
!
interface Loopback22
 ip address 200.2.2.2 255.255.0.0
!
interface Loopback23
 ip address 200.3.2.2 255.255.0.0
!
interface Loopback24
 ip address 200.4.2.2 255.255.0.0
!
interface Loopback25
 ip address 200.5.2.2 255.255.0.0

now we'll configure address summarization on R2 for this address

we'll configure this on R2 interface f0/1 only

R2(config)#int fa 0/1

R2(config-if)#ip summary-address eigrp 1 200.0.0.0 255.248.0.0

now show routing table from R1 and R2

R1>sh ip rou

..

D    200.0.0.0/13 [90/386560] via 192.168.1.2, 00:04:19, FastEthernet0/1

D    200.1.0.0/16 [90/389120] via 192.168.1.3, 00:00:21, FastEthernet0/1

D    200.2.0.0/16 [90/389120] via 192.168.1.3, 00:00:21, FastEthernet0/1

D    200.3.0.0/16 [90/389120] via 192.168.1.3, 00:00:21, FastEthernet0/1

D    200.4.0.0/16 [90/389120] via 192.168.1.3, 00:00:21, FastEthernet0/1

D    200.5.0.0/16 [90/389120] via 192.168.1.3, 00:00:21, FastEthernet0/1

R3#sh ip rou

..

D    200.0.0.0/13 [90/386560] via 192.168.1.2, 00:05:56, FastEthernet0/1

D    200.1.0.0/16 [90/156160] via 172.16.1.2, 00:01:59, FastEthernet0/0

D    200.2.0.0/16 [90/156160] via 172.16.1.2, 00:01:59, FastEthernet0/0

D    200.3.0.0/16 [90/156160] via 172.16.1.2, 00:01:59, FastEthernet0/0

D    200.4.0.0/16 [90/156160] via 172.16.1.2, 00:01:59, FastEthernet0/0

D    200.5.0.0/16 [90/156160] via 172.16.1.2, 00:01:59, FastEthernet0/0

you see, in green there's the summary route that we just manually create, but the un-summarize still being advertised.

now lets check we did it learned from, in red is where this specific was learned from ... owh, now we know why, they learn from network 172.16.1.x which is interface 0/0

let's just turn of this interface

R2(config)#int fa 0/0

R2(config-if)#shut

show routing table again, result should only show summarize route for network 200.0.0.0

R1#sh ip rou

..

C    192.168.1.0/24 is directly connected, FastEthernet0/1

D    200.0.0.0/13 [90/386560] via 192.168.1.2, 00:00:04, FastEthernet0/1

now our address summarization work fine ;) but that is for R1 and R3, I wonder what R2 routing table looks like, let see 

R2#sh ip rou

...

C    192.168.1.0/24 is directly connected, FastEthernet0/1

D    200.0.0.0/13 is a summary, 00:12:06, Null0

C    200.1.0.0/16 is directly connected, Loopback21

C    200.2.0.0/16 is directly connected, Loopback22

C    200.3.0.0/16 is directly connected, Loopback23

C    200.4.0.0/16 is directly connected, Loopback24

C    200.5.0.0/16 is directly connected, Loopback25

by right, it shouldn't be any summary because we configure the summary on fa0/1, in yellow there's one summary and at the end it mention Null 0 , what is this for?

actually if you notice, our summary is /13 , which mean it start from 200.0.0.0 - 200.7.255.255

but our network only start from 200.1.0.0 to 200.5.0.0 only, so all packet for the rest or un-existed network within /13 will be dropped(200.5..x.x - 200.7.x.x), that's Null 0 is for. this is to prevent the loop

happy routing ;) good luck to Liverpool later