Implement, Optimize and Troubleshoot Manual and Auto Summarization with any Routing Protocol
Auto Summarization is when a a prefix is automatically summarized at a network boundary to it’s classful prefix. Example, a router changes the prefix 172.16.5.0/24 to 172.16.0.0/16.
By default RIP will automatically summarize subnet routes into network level routes
router rip version 2 [no] auto-summary network x.x.x.x
Manual summarization can be done at an interface level. The summary entry will be entered into the RIP database
R1(config-if)#ip summary-address rip 18.104.22.168 255.255.255.0 R1(config-if)# R1#sh int lo0 Loopback0 is up, line protocol is up Hardware is Loopback Internet address is 22.214.171.124/32 R3#sh ip route 126.96.36.199/8 is variably subnetted, 2 subnets, 2 masks R 188.8.131.52/24 [120/2] via 184.108.40.206, 00:00:05, GigabitEthernet0/1 R 220.127.116.11/32 [120/2] via 18.104.22.168, 00:00:12, GigabitEthernet0/1 22.214.171.124/32 is subnetted, 1 subnets R 126.96.36.199 [120/1] via 188.8.131.52, 00:00:12, GigabitEthernet0/1 184.108.40.206/32 is subnetted, 1 subnets C 220.127.116.11 is directly connected, Loopback0 18.104.22.168/16 is variably subnetted, 3 subnets, 2 masks R 22.214.171.124/24 [120/1] via 126.96.36.199, 00:00:12, GigabitEthernet0/1 C 188.8.131.52/24 is directly connected, GigabitEthernet0/1 L 184.108.40.206/32 is directly connected, GigabitEthernet0/1 R3#
Auto summary is enabled in EIGRP by default.
Summary routers are given an administrative distance of 5
Manual summarization can be performed at any point in the network
R1(config-if)#ip summary-address eigrp 1 0.0.0.0/0 R3(config-router)#do sh ip route D* 0.0.0.0/0 [90/3328] via 220.127.116.11, 00:00:08, GigabitEthernet0/1
OSPF does not have an auto summaization feature and can only perform summarization at specific points in the network. OSPF requires at an area has a the same database on each router in that area which means summarization can only be done at area borders.
There are 2 types of summarization
Area range – ABR, summarize internal routes as they get passed to another area as a type 3 interarea LSA
Summary address – ASBR, summarize external routes before injecting them into the OSPF domain at type 5 external LSA’s
BGP has multiple different ways to summarize routes
network w/ static route
R1(config-router)#do sh run | s bgp router bgp 1 bgp log-neighbor-changes network 18.104.22.168 mask 255.255.255.255 aggregate-address 22.214.171.124 255.255.0.0 neighbor 126.96.36.199 remote-as 2 R1(config-router)#
R2(config-router)#do sh ip route bgp 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 a - application route + - replicated route, % - next hop override, p - overrides from PfR Gateway of last resort is not set 188.8.131.52/8 is variably subnetted, 2 subnets, 2 masks B 184.108.40.206/16 [20/0] via 220.127.116.11, 00:00:03 B 18.104.22.168/32 [20/0] via 22.214.171.124, 00:00:03 R2(config-router)# R2(config-router)#