Cisco CCNP BSCI Exam Tutorial EIGRP Route Summarization
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Cisco CCNP / BSCI Exam Guide: EIGRP Route Summarization
Overview
Mastering route summarization is essential for passing the BSCI exam and moving closer to your CCNP certification. While binary conversions are important, you must know how to apply summary routes correctly for each protocol. In recent tutorials, we've explored OSPF route summarization. Now, let’s focus on EIGRP.
Example Loopback Addresses
Consider these four loopback addresses:
- Loopback 16: 16.16.16.16 /32
- Loopback 17: 17.17.17.17 /32
- Loopback 18: 18.18.18.18 /32
- Loopback 19: 19.19.19.19 /32
These addresses will be configured in EIGRP AS 100 on router R1.
```plaintext
R1(config-if)
router eigrp 100
R1(config-router)network 16.16.16.16 0.0.0.0
R1(config-router)network 17.17.17.17 0.0.0.0
R1(config-router)network 18.18.18.18 0.0.0.0
R1(config-router)network 19.19.19.19 0.0.0.0
```On R3, an EIGRP neighbor, the routing table appears as follows:
```plaintext
R3
show ip route eigrp
17.0.0.0/32 is subnetted, 1 subnetsD 17.17.17.17 [90/2297856] via 172.12.123.1, 00:00:29, Serial0
16.0.0.0/32 is subnetted, 1 subnets
D 16.16.16.16 [90/2297856] via 172.12.123.1, 00:00:36, Serial0
19.0.0.0/32 is subnetted, 1 subnets
D 19.19.19.19 [90/2297856] via 172.12.123.1, 00:00:08, Serial0
18.0.0.0/32 is subnetted, 1 subnets
D 18.18.18.18 [90/2297856] via 172.12.123.1, 00:00:22, Serial0
```
Manual Route Summarization
To summarize the routes, convert the network addresses to binary and find the common bits. For these addresses, only the first octet is required in binary:
- 16: 00010000
- 17: 00010001
- 18: 00010010
- 19: 00010011
From left to right, the first six bits are common: 000100xx, which is 16 in decimal. To determine the summary mask, set a "1" for each common bit: 11111100. The resulting mask is 252.0.0.0, giving a summary address of 16.0.0.0 252.0.0.0.
Configuring EIGRP Summary Address
In EIGRP, the summary address is configured on an interface:
```plaintext
R1(config)
interface serial0
R1(config-if)ip summary-address eigrp 100 16.0.0.0 252.0.0.0
```Following this configuration, EIGRP adjacencies will momentarily drop and then restore:
```plaintext
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.3 (Serial0) is down: summary configured
02:40:17: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.3 (Serial0) is up: new adjacency
```
The process can affect network performance, so it’s recommended to summarize during non-peak hours.
Updated Routing Table on R3
Upon checking R3’s routing table again:
```plaintext
R3
show ip route eigrp
D 16.0.0.0/6 [90/2297856] via 172.12.123.1, 00:01:46, Serial0```
The individual routes are replaced by the summarized route with a /6 mask.
Conclusion
Understanding and applying route summarization effectively is a crucial skill for network professionals. Before taking the BSCI exam, ensure you can summarize routes across all core protocols.
You can find the original non-AI version of this article here: Cisco CCNP BSCI Exam Tutorial EIGRP Route Summarization.
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