Curriculum

CCNP ENARSI Labs

Lab 1 - Implement EIGRP for IPv4

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Lab 2 - Advanced EIGRP Features

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Lab 3 - Implement EIGRP for IPv6

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Lab 4 - Implement Single-Area OSPFv2

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Lab 5 - Implement Multi-Area OSPFv2

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Lab 6 - OSPFv2 Route Summarization and Filtering

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Lab 7 - OSPFv3 Multi-Area with AF

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Lab 8 - Implement eBGP for IPv4

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Text lesson

8.5 Configure and Verify Route Summarization with Atomic Aggregate and AS-Set

Step 1: Configure route summarization using atomic aggregate and AS-Set.

a. Shut down both serial interfaces on R1. This will create a single path from R1 (AS 1000) to R2 (AS 500) to R3 (AS 300).

R1(config)# interface s1/0

R1(config-if)# shutdown

R1(config-if)# exit

R1(config)# interface s1/1

R1(config-if)# shutdown

b. Remove route aggregation previously configured on R1.

R1(config)# router bgp 1000

R1(config-router)# no aggregate-address 192.168.1.0 255.255.255.0 summary-only

c. Verify that R3 is now receiving the non-summarized prefixes 192.168.1.0/27 and 192.168.1.64/26.

R3# show ip route 192.168.1.0

Routing entry for 192.168.1.0/24, 2 known subnets

Variably subnetted with 2 masks

B 192.168.1.0/27 [20/0] via 10.2.3.2, 00:01:26

B 192.168.1.64/26 [20/0] via 10.2.3.2, 00:01:26

d. On R2, summarize the prefixes 192.168.1.0/27 and 192.168.1.64/26 received from R1 as 192.168.1.0/24.

R2(config)# router bgp 500

R2(config-router)# aggregate-address 192.168.1.0 255.255.255.0 summary-only

Step 2: Verify route summarization using atomic aggregate and AS-Set.

a. Verify that R3 is receiving the aggregated prefix 192.168.1.0/24.

R3# show ip route bgp | begin Gateway

Gateway of last resort is not set

B 192.168.1.0/24 [20/0] via 10.2.3.2, 00:00:51

192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks

B 192.168.2.0/27 [20/0] via 10.2.3.2, 08:46:37

B 192.168.2.64/26 [20/0] via 10.2.3.2, 08:46:37

192.168.3.0/24 is variably subnetted, 5 subnets, 4 masks

B 192.168.3.0/24 [200/0], 08:46:07, Null0

b. Examine R3’s BGP table. Notice that the AS path only includes the AS that summarized the route, AS 500, router R2.

R3# show ip bgp

Network Next Hop Metric LocPrf Weight Path

*> 192.168.1.0 10.2.3.2 0 0 500 i

*> 192.168.2.0/27 10.2.3.2 0 0 500 i

*> 192.168.2.64/26 10.2.3.2 0 0 500 i

s> 192.168.3.0/27 0.0.0.0 0 32768 i

*> 192.168.3.0 0.0.0.0 32768 i

s> 192.168.3.64/26 0.0.0.0 0 32768 i

c. On R2, remove the current route aggregation for the 192.168.1.0/24 prefix and configure it again, this time using the as-set option.

R2(config)# router bgp 500

R2(config-router)# no aggregate-address 192.168.1.0 255.255.255.0 summary-only

R2(config-router)# aggregate-address 192.168.1.0 255.255.255.0 as-set summary-only

d. Verify that R3 is receiving the aggregated prefix 192.168.1.0/24.

R3# show ip route bgp | begin Gateway

Gateway of last resort is not set

B 192.168.1.0/24 [20/0] via 10.2.3.2, 00:01:35

192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks

B 192.168.2.0/27 [20/0] via 10.2.3.2, 08:50:02

B 192.168.2.64/26 [20/0] via 10.2.3.2, 08:50:02

192.168.3.0/24 is variably subnetted, 5 subnets, 4 masks

B 192.168.3.0/24 [200/0], 08:49:32, Null0

e. Examine R3’s BGP table again. Notice that the entry for 192.168.1.0 this time includes the entire AS path. The output from the show ip bgp 192.168.1.0 command displays both AS numbers and identifies that R2 (2.2.2.2) aggregated the route.

R3# show ip bgp

Network Next Hop Metric LocPrf Weight Path

*> 192.168.1.0 10.2.3.2 0 0 500 1000 i

*> 192.168.2.0/27 10.2.3.2 0 0 500 i

*> 192.168.2.64/26 10.2.3.2 0 0 500 i

s> 192.168.3.0/27 0.0.0.0 0 32768 i

*> 192.168.3.0 0.0.0.0 32768 i

s> 192.168.3.64/26 0.0.0.0 0 32768 i

R3# show ip bgp 192.168.1.0 | begin Refresh

Refresh Epoch 7

500 1000, (aggregated by 500 2.2.2.2)

10.2.3.2 from 10.2.3.2 (2.2.2.2)

Origin IGP, metric 0, localpref 100, valid, external, best

rx pathid: 0, tx pathid: 0x0