EIGRP Route Manipulation

Question 1

Route Manipulation

Answer 1

Route manipulation involves selectively identifying routes that are advertised or received from neighbor routers. The routes can be modified to alter traffic patterns or removed to reduce memory utilization or to improve security.

Question 2

Route Filtering Options

Answer 2

EIGRP supports filtering of routes as they are received or advertised from an interface.

Filtering of routes can be matched against:

1. ACLs
2. IP Prefix Lists
3. Route Maps
4. Gateway IP Addresses

Question 3

Inbound and Outbound Filtering

Answer 3

Inbound filtering drops routes prior to the DUAL processing, which results in the routes not being installed into the RIB because they are not known.

However, if the filtering occurs during outbound route advertisement, the routes are processed by DUAL and are installed into the local RIB of the advertising router.

Question 4

Example

Answer 4

Inbound filtering of 10.1.100.0/24 and outbound filtering of 10.3.100.0/24.

The inbound filter uses a standard ACL to filter inbound routes and a prefix list to filter outbound advertisements.

Question 5

Offset Lists

Answer 5

Modifying the EIGRP path metric provides traffic engineering in EIGRP.

Modifying the delay setting for an interface modifies all routes that are received and advertised from that router’s interface.

Offset lists allow for the modification of route attributes based on the direction of the update, a specific prefix, or a combination of direction and prefix.

Question 6

Example

Answer 6

To demonstrate how an offset list is used to steer traffic, the path metric for the 10.1.100.0/24 network is incremented on R2’s Gi0/1 interface so that R2 forwards packets toward R3 for that network.

In addition, the 10.3.100.0/24 network is incremented on R2’s Gi0/3 interface so that R2 forwards packets toward R1 for that network.

• router eigrp 100
• offset-list R1 in 200000 GigabitEthernet0/1
• offset-list R3 in 200000 GigabitEthernet0/3

offset-list offset-value {acl-number | acl-name] {in | out} [interface-id] to modify the metric value of a route.