Route summarization

Route summarization

Route Summarization is the process of combining the contagious networks into one sub large network. Route summarization also called route aggregation, route summarization help to minimizing the routing table in an IP networks, summarization use less resources like memory, processor, and bandwidth.

Types of summarization:

1.       1.Auto summary

             Auto summarization is done to a default classful boundary

§  Class A       /8

§  Class B       /16

§  Class C       /24

             Routing protocol like RIPv2, EIGRP, and BGP v4 support               auto summarization and can be disable by the command                    R1(config-router)#no auto-summary

       

        2.Manual summary

        Administrator manually configure summarization to specific             boundary

         

       Manual summarization is supported by all classless routing               protocols like EIGRP, OSPF, RIPv2, and BGP.

 

 Steps for calculating manual summarization:      

Calculate the summary address formula you can use: 256 – number of networks = subnet mask for summary address.

Example: we want to create the most optimal summary for the following 4 networks:

192.168.0.0 / 24 subnet mask 255.255.255.0

192.168.1.0 / 24 subnet mask 255.255.255.0

192.168.2.0 / 24 subnet mask 255.255.255.0

192.168.3.0 / 24 subnet mask 255.255.255.0

 Convert these network addresses to binary:

192.168.0.0	11000000	10101000	00000000	00000000
192.168.1.0	11000000	10101000	00000001	00000000
192.168.2.0	11000000	10101000	00000010	00000000
192.168.3.0	11000000	10101000	00000011	00000000

Now we can see how many bits these network addresses have in common. The first and second octets are having the same, so that’s 16 bits.

Take a look in the third octet:

00000000

00000001

00000010

00000011

You see the first 6 bits of the third octet are the same. Now create our summary address. Calculate 8 + 8 + 6 = 22 bits

Our summary address will be 192.168.0.0 /22 (subnet mask 255.255.252.0).

Now we have seen how to do this in binary, now we do it in decimal. It is a simple trick you can use to calculate this summary.

As you see we have 4 networks, or it’s a block of 4.

 Here is a formula you can use:

256 - Number of networks = subnet mask for summary address.

For our example: 256 - 4 networks = 252

So the subnet mask will be 255.255.252.0

Another way to see at it is by using the CIDR notation. We know a /24 is a block of 256 addresses.  Using a /23 means we have 2 x 256, and a /22 means we have 4 x 256.

lets configure summarization in EIGRP

Topology 

goal:

configure EIGRP 100 on R1, R2, R3, and R4. Advertise the interface as per the diagram

configure manual summarization of above networks as per the calculation.

R1(config)#router eigrp 100

R1(config-router)#network 10.0.0.0

R1(config-router)#network 11.0.0.0

R1(config-router)#no auto-summary

R2(config)#router eigrp 100

R2(config-router)#network 20.0.0.0

R2(config-router)#network 10.0.0.0

R2(config-router)#network 10.0.0.0

.R2(config-router)#network 30.0.0.0

R2(config-router)#no auto-summary

R3(config)#router eigrp 100

R3(config-router)#network 13.0.0.0

R3(config-router)#network 30.0.0.0

R3(config-router)#no auto-summary

R4(config)#router eigrp 100

R4(config-router)#network 20.0.0.0

R4(config-router)#network 14.0.0.0

R4(config-router)#no auto-summary

R1#show 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

      12.0.0.0/24 is subnetted, 4 subnets

D        12.0.0.0 [90/2297856] via 10.1.1.2, 00:00:09, Serial3/0

D        12.0.1.0 [90/2297856] via 10.1.1.2, 00:00:09, Serial3/0

D        12.0.2.0 [90/2297856] via 10.1.1.2, 00:00:09, Serial3/0

D        12.0.3.0 [90/2297856] via 10.1.1.2, 00:00:09, Serial3/0

      13.0.0.0/24 is subnetted, 4 subnets

D        13.0.0.0 [90/2809856] via 10.1.1.2, 00:10:47, Serial3/0

D        13.0.1.0 [90/2809856] via 10.1.1.2, 00:10:47, Serial3/0

D        13.0.2.0 [90/2809856] via 10.1.1.2, 00:10:47, Serial3/0

D        13.0.3.0 [90/2809856] via 10.1.1.2, 00:10:47, Serial3/0

      14.0.0.0/24 is subnetted, 4 subnets

D        14.0.0.0 [90/2809856] via 10.1.1.2, 00:09:50, Serial3/0

D        14.0.1.0 [90/2809856] via 10.1.1.2, 00:09:50, Serial3/0

D        14.0.2.0 [90/2809856] via 10.1.1.2, 00:09:50, Serial3/0

D        14.0.3.0 [90/2809856] via 10.1.1.2, 00:09:50, Serial3/0

D     20.0.0.0/8 [90/2681856] via 10.1.1.2, 00:11:31, Serial3/0

D     30.0.0.0/8 [90/2681856] via 10.1.1.2, 00:11:24, Serial3/0

  

R2#show 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

      11.0.0.0/24 is subnetted, 4 subnets

D        11.0.0.0 [90/2297856] via 10.0.0.1, 00:12:32, Serial3/0

D        11.0.1.0 [90/2297856] via 10.0.0.1, 00:12:32, Serial3/0

D        11.0.2.0 [90/2297856] via 10.0.0.1, 00:12:32, Serial3/0

D        11.0.3.0 [90/2297856] via 10.0.0.1, 00:12:32, Serial3/0

      13.0.0.0/24 is subnetted, 4 subnets

D        13.0.0.0 [90/2297856] via 30.1.1.2, 00:11:48, Serial3/1

D        13.0.1.0 [90/2297856] via 30.1.1.2, 00:11:48, Serial3/1

D        13.0.2.0 [90/2297856] via 30.1.1.2, 00:11:48, Serial3/1

D        13.0.3.0 [90/2297856] via 30.1.1.2, 00:11:48, Serial3/1

      14.0.0.0/24 is subnetted, 4 subnets

D        14.0.0.0 [90/2297856] via 20.1.1.2, 00:10:51, Serial3/2

D        14.0.1.0 [90/2297856] via 20.1.1.2, 00:10:51, Serial3/2

D        14.0.2.0 [90/2297856] via 20.1.1.2, 00:10:51, Serial3/2

D        14.0.3.0 [90/2297856] via 20.1.1.2, 00:10:51, Serial3/2

R3#show 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 [90/2681856] via 30.1.1.1, 00:12:21, Serial3/1

      11.0.0.0/24 is subnetted, 4 subnets

D        11.0.0.0 [90/2809856] via 30.1.1.1, 00:12:21, Serial3/1

D        11.0.1.0 [90/2809856] via 30.1.1.1, 00:12:21, Serial3/1

D        11.0.2.0 [90/2809856] via 30.1.1.1, 00:12:21, Serial3/1

D        11.0.3.0 [90/2809856] via 30.1.1.1, 00:12:21, Serial3/1

      12.0.0.0/24 is subnetted, 4 subnets

D        12.0.0.0 [90/2297856] via 30.1.1.1, 00:01:42, Serial3/1

D        12.0.1.0 [90/2297856] via 30.1.1.1, 00:01:42, Serial3/1

D        12.0.2.0 [90/2297856] via 30.1.1.1, 00:01:42, Serial3/1

D        12.0.3.0 [90/2297856] via 30.1.1.1, 00:01:42, Serial3/1

      14.0.0.0/24 is subnetted, 4 subnets

D        14.0.0.0 [90/2809856] via 30.1.1.1, 00:11:23, Serial3/1

D        14.0.1.0 [90/2809856] via 30.1.1.1, 00:11:23, Serial3/1

D        14.0.2.0 [90/2809856] via 30.1.1.1, 00:11:23, Serial3/1

D        14.0.3.0 [90/2809856] via 30.1.1.1, 00:11:23, Serial3/1

D     20.0.0.0/8 [90/2681856] via 30.1.1.1, 00:12:21, Serial3/1

R4#show 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 [90/2681856] via 20.1.1.1, 00:12:03, Serial3/2

      11.0.0.0/24 is subnetted, 4 subnets

D        11.0.0.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        11.0.1.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        11.0.2.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        11.0.3.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

      12.0.0.0/24 is subnetted, 4 subnets

D        12.0.0.0 [90/2297856] via 20.1.1.1, 00:02:15, Serial3/2

D        12.0.1.0 [90/2297856] via 20.1.1.1, 00:02:15, Serial3/2

D        12.0.2.0 [90/2297856] via 20.1.1.1, 00:02:15, Serial3/2

D        12.0.3.0 [90/2297856] via 20.1.1.1, 00:02:15, Serial3/2

      13.0.0.0/24 is subnetted, 4 subnets

D        13.0.0.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        13.0.1.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        13.0.2.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D        13.0.3.0 [90/2809856] via 20.1.1.1, 00:12:03, Serial3/2

D     30.0.0.0/8 [90/2681856] via 20.1.1.1, 00:12:03, Serial3/2

R1(config)#interface serial 3/0

R1(config-if)#ip summary-address eigrp 100 11.0.0.0 255.255.252.0

R2(config)#interface serial 3/0

R2(config-if)#ip summary-address eigrp 100 12.0.0.0 255.255.252.0

R2(config-if)#interface serial 3/1
R2(config-if)#ip summary-address eigrp 100 12.0.0.0 255.255.252.0
R2(config-if)#interface serial 3/2
R2(config-if)#ip summary-address eigrp 100 12.0.0.0 255.255.252.0

R3(config)#interface serial 3/1

R3(config-if)#ip summary-address eigrp 100 13.0.0.0 255.255.252.0

R4(config)#interface serial 3/2

R4(config-if)#ip summary-address eigrp 100 14.0.0.0 255.255.252.0

R1#show 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

      11.0.0.0/8 is variably subnetted, 9 subnets, 3 masks

D        11.0.0.0/22 is a summary, 00:03:20, Null0

      12.0.0.0/22 is subnetted, 1 subnets

D        12.0.0.0 [90/2297856] via 10.1.1.2, 00:02:43, Serial3/0

      13.0.0.0/22 is subnetted, 1 subnets

D        13.0.0.0 [90/2809856] via 10.1.1.2, 00:01:41, Serial3/0

      14.0.0.0/22 is subnetted, 1 subnets

D        14.0.0.0 [90/2809856] via 10.1.1.2, 00:01:14, Serial3/0

D     20.0.0.0/8 [90/2681856] via 10.1.1.2, 00:19:14, Serial3/0

D     30.0.0.0/8 [90/2681856] via 10.1.1.2, 00:19:07, Serial3/0

R2#show 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

      11.0.0.0/22 is subnetted, 1 subnets

D        11.0.0.0 [90/2297856] via 10.0.0.1, 00:03:32, Serial3/0

      12.0.0.0/8 is variably subnetted, 9 subnets, 3 masks

D        12.0.0.0/22 is a summary, 00:02:55, Null0

      13.0.0.0/22 is subnetted, 1 subnets

D        13.0.0.0 [90/2297856] via 30.1.1.2, 00:01:53, Serial3/1

      14.0.0.0/22 is subnetted, 1 subnets

D        14.0.0.0 [90/2297856] via 20.1.1.2, 00:01:26, Serial3/2

R3#show 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 [90/2681856] via 30.1.1.1, 00:18:56, Serial3/1

      11.0.0.0/22 is subnetted, 1 subnets

D        11.0.0.0 [90/2809856] via 30.1.1.1, 00:03:45, Serial3/1

      12.0.0.0/22 is subnetted, 1 subnets

D        12.0.0.0 [90/2297856] via 30.1.1.1, 00:02:38, Serial3/1

      13.0.0.0/8 is variably subnetted, 9 subnets, 3 masks

D        13.0.0.0/22 is a summary, 00:02:07, Null0

      14.0.0.0/22 is subnetted, 1 subnets

D        14.0.0.0 [90/2809856] via 30.1.1.1, 00:01:39, Serial3/1

D     20.0.0.0/8 [90/2681856] via 30.1.1.1, 00:18:56, Serial3/1

R4#show  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 [90/2681856] via 20.1.1.1, 00:18:15, Serial3/2

      11.0.0.0/22 is subnetted, 1 subnets

D        11.0.0.0 [90/2809856] via 20.1.1.1, 00:03:55, Serial3/2

      12.0.0.0/22 is subnetted, 1 subnets

D        12.0.0.0 [90/2297856] via 20.1.1.1, 00:02:55, Serial3/2

      13.0.0.0/22 is subnetted, 1 subnets

D        13.0.0.0 [90/2809856] via 20.1.1.1, 00:02:16, Serial3/2

      14.0.0.0/8 is variably subnetted, 9 subnets, 3 masks

D        14.0.0.0/22 is a summary, 00:01:49, Null0

D     30.0.0.0/8 [90/2681856] via 20.1.1.1, 00:18:15, Serial3/2

 R1#ping 14.0.0.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 14.0.0.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 36/40/56 ms

R1#ping 13.0.0.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 13.0.0.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 28/60/76 ms

R1#ping 12.0.0.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.0.0.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/40 ms

 R4#traceroute 13.0.0.1

Type escape sequence to abort.

Tracing the route to 13.0.0.1

VRF info: (vrf in name/id, vrf out name/id)

  1 20.1.1.1 40 msec 68 msec 60 msec

  2 30.1.1.2 144 msec 144 msec 64 msec