Manual Summarization
• Configurable on a per-interface basis in any router within network
• When summarization is configured on an interface, the router immediately creates a route pointing to Null (0)
- Loop prevention mechanism
• When the last specific route of the summary goes away, the summary is deleted
• The minimum metric of the specific routes is used as the metric of the summary route
© 2002, CiscoSystems, Inc. All rights reserved. Cisco CCIE Prep v1.0—Module 6-57
EIGRP manual summarization is critical to large EIGRP networks. It limits the EIGRP query and can significantly reduce the size of the routing table. There are essentially two ways to deploy manual summarization:
Advertise a summary address or aggregate address with the following interface command: ip summary-address eigrp asnumber summaryaddress addressmask Advertise a default summary route, with the following interface command: ip summary-address eigrp as number 0.0.0.0 0.0.0.0.
This command will cause only the default route to be advertised and all other routing updates will be suppressed.
Note In Cisco IOS 12.0(4)T, an administrative distance can be added to the summary address to alter the default admin distance of 90.
EIGRP Stub Networks
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets C 172.16.70.0 is directly connected, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets C 10.1.1.0 is directly connected, ATM0
7.0.0.0/24 is subnetted, 1 subnets C 7.7.7.0/24 is directly connected, Loopback0
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets C 172.16.70.0 is directly connected, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets C 10.1.1.0 is directly connected, ATM0
7.0.0.0/24 is subnetted, 1 subnets C 7.7.7.0/24 is directly connected, Loopback0
© 2002, Cisco Systems, Inc. All rights reserved. Cisco CCIE Prep v1.0—Module 6-58
In Cisco IOS Software Release 12.0(7)T, Cisco introduced EIGRP stub routing to further control stability and reduce resource utilization. This feature was fully integrated into Release 12.0(15)S. EIGRP stub routing functions like that of an OSPF stub area. The stub router will have one exit path from the routing domain and forward all traffic to a central or distribution router. Another way to say this is that the stub network cannot be a transit router for EIGRP, and it can have only one EIGRP neighbor.
When configuring EIGRP stub routing, only the remote or the spoke router needs to be configured as a stub. This router will respond to queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the message "inaccessible". This process greatly reduces the overhead associated with responding to queries by the remote routers. The stub router will also send special peer information to its neighbor informing its neighbor that it is a stub router.
To configure an EIGRP stub routing, use the following router command under EIGRP. router(config-router)# eigrp stub [receive-only | connected | static | summary]
The options are described as follows:
■ Receive-only: Causes the router to not send any routes.
■ Connected: The router advertises all connected routes to the single neighbor. No redistribution is necessary.
■ Static: The router advertises all static routes to a single neighbor. The static routes still need to be redistributed into EIGRP to be advertised.
■ Summary: The router advertises summary routes.
To verify that the router is configured as an EIGRP stub router, use the show ip eigrp neighbor detail command. The last line of the output will show if stub routing is enabled, and what the stub router can advertise. The show eigrp packet stub will show debug information about the stub status of the peer routers.
Continue reading here: Multiplier is the number specified by the variance command
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