Questions
Introduction
Does EIGRP require a default network to propagate a default route?
Should I always use the eigrp log-neighbor-changes command when I configure EIGRP?
Does EIGRP support secondary addresses?
What debugging capabilities does EIGRP have?
What does the word serno mean on the end of an EIGRP topology entry when you issue the show ip eigrp topology command?
What percent of bandwidth and processor resources does EIGRP use?
Does EIGRP support aggregation and variable length subnet masks?
Does EIGRP support areas?
Can I configure more than one EIGRP autonomous system on the same router?
If there are two EIGRP processes that run and two equal paths are learned, one by each EIGRP process, do both routes get installed?
What does the EIGRP stuck in active message mean?
What does the neighbor statement in the EIGRP configuration section do?
Why does the EIGRP passive-interface command remove all neighbors for an interface?
Why are routes received from one neighbor on a point-to-multipoint interface that runs EIGRP not propagated to another neighbor on the same point-to-multipoint interface?
When I configure EIGRP, how can I configure a network statement with a mask?
I have two routes: 172.16.1.0/24 and 172.16.1.0/28. How can I deny 172.16.1.0/28 while I allow 172.16.1.0/24 in EIGRP?
I have a router that runs Cisco Express Forwarding (CEF) and EIGRP. Who does load-balancing when there are multiple links to a destination?
How can I use only one path when a router has two equal cost paths?
What is the difference in metric calculation between EIGRP and IGRP?
What is the EIGRP Stub Routing feature?
How can I send a default route to the Stub router from the hub?
How EIGRP behaves over a GRE tunnel compared to a directly connected network?
What is an offset-list, and how is it useful?
How can I tag external routes in EIGRP?
What are the primary functions of the PDM?
What are the various load-balancing options available in EIGRP?
Related Information
Introduction
Q. Does EIGRP require a default network to propagate a default route?
Q. Should I always use the eigrp log-neighbor-changes command when I configure EIGRP?
Q. Does EIGRP support secondary addresses?
Q. What debugging capabilities does EIGRP have?
Q. What does the word serno mean on the end of an EIGRP topology entry when you issue the show ip eigrp topology command?
show ip eigrp topology P 172.22.71.208/29, 2 successors, FD is 46163456 via 172.30.1.42 (46163456/45651456), Serial0.2, serno 7539273 via 172.30.2.49 (46163456/45651456), Serial2.6, serno 7539266These sernos are local to the router and are not passed with the routing update.
Q. What percent of bandwidth and processor resources does EIGRP use?
A. EIGRP version 1 introduced a feature that prevents any single EIGRP process from using more than fifty percent of the configured bandwidth on any link during periods of network convergence. Each AS or protocol (for instance, IP, IPX, or Appletalk) serviced by EIGRP is a separate process. You can use the ip bandwidth-percent eigrp interface configuration command in order to properly configure the bandwidth statement on each WAN interface. Refer to the EIGRP White Paper for more details on how this feature works.
In addition, the implementation of partial and incremental updates means that EIGRP sends routing information only when a topology change occurs. This feature significantly reduces bandwidth use.
The feasible successor feature of EIGRP reduces the amount of processor resources used by an autonomous system (AS). It requires only the routers affected by a topology change to perform route re-computation. The route re-computation only occurs for routes that were affected, which reduces search time in complex data structures.
Q. Does EIGRP support aggregation and variable length subnet masks?
Q. Does EIGRP support areas?
Q. Can I configure more than one EIGRP autonomous system on the same router?
Q. If there are two EIGRP processes that run and two equal paths are learned, one by each EIGRP process, do both routes get installed?
Q. What does the EIGRP stuck in active message mean?
- The route reported by the SIA has gone away.
- An EIGRP neighbor (or neighbors) have not replied to the query for that route.
When the SIA occurs, the router clears the neighbor that did not reply to the query. When this happens, determine which neighbor has been cleared. Keep in mind that this router can be many hops away. Refer to What Does the EIGRP DUAL-3-SIA Error Message Mean? for more information.
Q. What does the neighbor statement in the EIGRP configuration section do?
Q. Why does the EIGRP passive-interface command remove all neighbors for an interface?
A. The passive-interface command disables the transmission and receipt of EIGRP hello packets on an interface. Unlike IGRP or RIP, EIGRP sends hello packets in order to form and sustain neighbor adjacencies. Without a neighbor adjacency, EIGRP cannot exchange routes with a neighbor. Therefore, the passive-interface command prevents the exchange of routes on the interface. Although EIGRP does not send or receive routing updates on an interface configured with the passive-interface command, it still includes the address of the interface in routing updates sent out of other non-passive interfaces. Refer to How Does the Passive Interface Feature Work in EIGRP? for more information.
Q. Why are routes received from one neighbor on a point-to-multipoint interface that runs EIGRP not propagated to another neighbor on the same point-to-multipoint interface?
- Split horizon behavior is turned on by default.
- When you change the EIGRP split horizon setting on an interface, it resets all adjacencies with EIGRP neighbors reachable over that interface.
- Split horizon should only be disabled on a hub site in a hub-and-spoke network.
- Disabling split horizon on the spokes radically increases EIGRP memory consumption on the hub router, as well as the amount of traffic generated on the spoke routers.
- The EIGRP split horizon behavior is not controlled or influenced by the ip split-horizon command.
For more details on split horizon and poison reverse, refer to Split Horizon and Poison Reverse. For more information on commands, refer to EIGRP Commands.
Q. When I configure EIGRP, how can I configure a network statement with a mask?
Q. I have two routes: 172.16.1.0/24 and 172.16.1.0/28. How can I deny 172.16.1.0/28 while I allow 172.16.1.0/24 in EIGRP?
A. In order to do this you need to use a prefix-list as shown here:
router eigrp 100 network 172.16.0.0 distribute-list prefix test in auto-summary no eigrp log-neighbor-changes ! ip prefix-list test seq 5 permit 172.16.1.0/24This allows only the 172.16.1.0/24 prefix and therefore denies 172.16.1.0/28.
Q. I have a router that runs Cisco Express Forwarding (CEF) and EIGRP. Who does load-balancing when there are multiple links to a destination?
A. The way in which CEF works is that CEF does the switching of the packet based on the routing table which is populated by the routing protocols such as EIGRP. In short, CEF does the load-balancing once the routing protocol table is calculated. Refer to How does load-balancing work? for more details on load balancing.
Q. How can I use only one path when a router has two equal cost paths?
Q. What is the difference in metric calculation between EIGRP and IGRP?
Q. What is the EIGRP Stub Routing feature?
A. The Stub routing feature is used to conserve bandwidth by summarizing and filtering routes. Only specified routes are propagated from the remote (Stub) router to the distribution router because of the Stub routing feature. For more information about the stub routing feature, refer to EIGRP Stub Routing. The EIGRP stub feature can be configured on the switch with the eigrp stub command, and it can be removed with the no eigrp stub. When you remove the eigrp stub command from the switch, the switch that runs the IP Base image throws the error:
EIGRP is restricted to stub configurations onlyThis issue can be resolved if you upgrade to Advanced Enterprise Images. This error is documented in CSCeh58135.
Q. How can I send a default route to the Stub router from the hub?
Q. How EIGRP behaves over a GRE tunnel compared to a directly connected network?
Q. What is an offset-list, and how is it useful?
Q. How can I tag external routes in EIGRP?
A. You can tag only routes that EIGRP has learned from another routing protocol.
Q. What are the primary functions of the PDM?
- Maintaining the neighbor and yopology tables of EIGRP routers that belong to that protocol suite
- Building and translating protocol specific packets for DUAL
- Interfacing DUAL to the protocol specific routing table
- Computing the metric and passing this information to DUAL; DUAL handles only the picking of the feasible successors (FSs)
- Implement filtering and access-lLists.
- Perform redistribution functions to/from other routing protocols.
Q. What are the various load-balancing options available in EIGRP?
Related Information
Updated: Jul 21, 2008 | Document ID: 1368 |