notes: EIGRP Summarization

- EIGRP by default, auto-summarizes prefixes to classful boundary when passing major network boundary, but this can be disabled. If auto-summary is enabled, interfaces are summarized at class boundary.
- A route to Null0 for summary routes are created to prevent black-holes.
- Disabling automatic summarization can prevent ambiguous routing between similar network subnets. (It is always recommended)

Manual summarization for EIGRP is interface-specific.

- This provides the flexibility to be able to advertise different summary routes out different interfaces for the same process.
- Manual summarization is configured with the "ip summary-address eigrp" command
- By default this will automatically suppress the advertisement of the more specific networks and create a route to Null0
- To have more specific routes sent, use a leak-map.
- The summary routes advertised into EIGRP are not tagged as external routes, like OSPF.
- The floating summary route is created by applying a default route and an administrative distance at the interface level.

command:

- Disables auto-summary to the classful boundary when passing between major network boundaries (default = Enabled)

no auto-summary

- Will automatically suppress the advertisement of the more specific networks
- Specifies the summary, mask, and the process into which the summary is to be advertised
- [leak-map]:Route-map allows more specific routes + summary to be advertised

int E0
ip summary-address eigrp {ASN} {aggregate} [leak-map] [AD]

- Example of a floating summary route with a higher AD.

ip summary-address eigrp 100 0.0.0.0 0.0.0.0 250