© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Configuring EIGRP Using EIGRP in an Enterprise Network

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Factors That Influence EIGRP Scalability Quantity of routing information exchanged between peers; without proper route summarization, this can be excessive. Number of routers that must be involved when a topology change occurs. Depth of topology: the number of hops that information must travel to reach all routers. Number of alternate paths through the network.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v EIGRP Query Process Queries are sent when a route is lost and no feasible successor is available. The lost route is now in active state. Queries are sent to all neighboring routers on all interfaces except the interface to the successor. If the neighbors do not have the lost-route information, queries are sent to their neighbors. If a router has an alternate route, it answers the query; this stops the query from spreading in that branch of the network.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Updates and Queries in Hub-and-Spoke Topology You do not want to use these paths!

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v EIGRP Stub The EIGRP stub routing feature improves network stability, reduces resource utilization, and simplifies remote router (spoke) configuration. Stub routing is commonly used in a hub-and-spoke topology. A stub router sends a special peer information packet to all neighboring routers to report its status as a stub router. A neighbor that receives a packet informing it of the stub status does not query the stub router for any routes.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Configuring EIGRP Stub receive-only: Prevents the stub from sending any type of route. connected: Permits stub to send connected routes (may still need to redistribute). static: Permits stub to send static routes (must still redistribute). summary: Permits stub to send summary routes. Default is connected and summary. eigrp stub [receive-only|connected|static|summary] Router(config-router)#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Limiting Updates and Queries: Using EIGRP Stub

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Example: eigrp stub Parameters If stub connected is configured: B will advertise /24 to A. B will not advertise /23, /23, or /24. If stub summary is configured: B will advertise /23 to A. B will not advertise /24, /24, or /24.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Example: eigrp stub Parameters (Cont.) If stub static is configured: B will advertise /24 to A. B will not advertise /24, /23, or /24. If stub receive-only is configured: B will not advertise anything to A, so A needs to have a static route to the networks behind B to reach them.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v EIGRP Query Process Stuck in Active The router has to get all the replies from the neighbors with an outstanding query before the router calculates the successor information. If any neighbor fails to reply to the query within 3 minutes by default, the route is SIA, and the router resets the neighbor relationship with the neighbor that fails to reply.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Active Process Enhancement Before Router A resets relationship to router B when the normal active timer expires. However, the problem is the link between router B and C. After Router A sends an SIA-Query at half of the normal active timer. Router B acknowledges the query there by keeping the relationship up.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Graceful Shutdown

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Summary Factors that affect network scalability include these: –Amount of information exchanged between neighbors –Number of routers –Depth of the topology –Number of alternate paths through the network When a route is lost and no feasible successor is available, queries are sent to all neighboring routers on all interfaces. The eigrp stub command is used to enable the stub routing feature, which improves network stability, reduces resource utilization, and simplifies stub router configuration.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Summary (Cont.) After a route goes active and the query sequence is initiated, it can only come out of the active state and move to passive state when it receives a reply for every generated query. If the router does not receive a reply to all the outstanding queries within 3 minutes (the default time), the route goes to the SIA state. The active process enhancement feature enables an EIGRP router to monitor the progression of the search for a successor route so that neighbor relationships are not reset unnecessarily. With graceful shutdown, a goodbye message is broadcast when an EIGRP routing process is shut down, to inform adjacent peers about the impending topology change.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v