The 0. Routing to Device-C is restored. If Device-A loses the connection to Device-B, Device-B will continue to advertise a default route to Device-C, which allows traffic to continue to reach destinations attached to Device-B. However, traffic destined to networks connected to Device-A or behind Device-A will be dropped when the traffic reaches Device-B. The figure below shows a network with two connections from the core, Device-A and Device-D. If the connection between Device-E and Device-C fails, the network will continue to operate normally.
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The 0. Routing to Device-C is restored. If Device-A loses the connection to Device-B, Device-B will continue to advertise a default route to Device-C, which allows traffic to continue to reach destinations attached to Device-B.
However, traffic destined to networks connected to Device-A or behind Device-A will be dropped when the traffic reaches Device-B. The figure below shows a network with two connections from the core, Device-A and Device-D.
If the connection between Device-E and Device-C fails, the network will continue to operate normally. Figure 2. To avoid this problem, you should configure the summary address with an administrative distance only on single-homed remote devices or areas that have only one exit point between two segments of the network. If two or more exit points exist from one segment of the network to another , configuring the floating default route can result in the formation of a black hole route a route that has quick packet dropping capabilities.
Hello Packets and the Hold-Time Intervals You can adjust the interval between hello packets and the hold time. Routing devices periodically send hello packets to each other to dynamically learn of other devices on their directly attached networks. This information is used to discover neighbors and to learn when neighbors become unreachable or inoperative.
By default, hello packets are sent every 5 seconds. The exception is on low-speed, nonbroadcast multiaccess NBMA media, where the default hello interval is 60 seconds.
Low speed is considered to be a rate of T1 or slower, as specified with the bandwidth interface configuration command. The default hello interval remains 5 seconds for high-speed NBMA networks. These networks are considered NBMA only if the interface has not been configured to use physical multicasting.
You can configure the hold time on a specified interface for a particular EIGRP routing process designated by the autonomous system number. The hold time is advertised in hello packets and indicates to neighbors the length of time they should consider the sender valid.
The default hold time is three times the hello interval or 15 seconds. For slow-speed NBMA networks, the default hold time is seconds. On very congested and large networks, the default hold time might not be sufficient for all devices to receive hello packets from their neighbors. In such cases, you may want to increase the hold time. Note Do not adjust the hold time without informing your technical support personnel. When split horizon is enabled on an interface, update and query packets are not sent to destinations for which this interface is the next hop.
Controlling update and query packets in this manner reduces the possibility of routing loops. By default, split horizon is enabled on all interfaces.
Split horizon blocks route information from being advertised by a device out of any interface from which that information originated. This behavior usually optimizes communications among multiple routing devices, particularly when links are broken. However, with nonbroadcast networks such as Frame Relay and SMDS , situations can arise for which this behavior is less than ideal. In such situations and in networks that have EIGRP configured, you may want to disable split horizon.
EIGRP, by default, sets the local outbound interface as the next-hop value while advertising a network to a peer, even when advertising routes out of the interface on which the routes were learned. This default setting can be disabled by using the no ip next-hop-self command in autonomous system configurations or the no next-hop-self command in named configurations.
When the next-hop self command is disabled, EIGRP does not advertise the local outbound interface as the next hop if the route has been learned from the same interface. Instead, the received next-hop value is used to advertise learned routes. If the first entry shows that the route being advertised is learned on the same interface, then the received next hop is used to advertise the route.
The no next-hop-self configuration ignores subsequent entries in the table, which may result in the no-next-hop-self configuration being dishonored on other interfaces. When this keyword is used, all routes to a network in the EIGRP table are evaluated to check whether routes advertised from an interface were learned on the same interface. If a route advertised by an interface was learned on the same interface, the no next-hop-self configuration is honored and the received next hop is used to advertise this route.
Link Bandwidth Percentage By default, EIGRP packets consume a maximum of 50 percent of the link bandwidth when configured with the bandwidth interface configuration command for autonomous system configurations and with the bandwidth-percent command for named configurations.
You might want to change the bandwidth value if a different level of link utilization is required or if the configured bandwidth does not match the actual link bandwidth which may have been configured to influence route metric calculations. EIGRP vNETs The EIGRP vNET feature uses Layer 3 routing techniques to provide limited fate sharing the term fate sharing refers to the failure of interconnected systems; that is, different elements of a network are interconnected in such a way that they either fail together or not at all , traffic isolation, and access control with simple configurations.
The vNET feature allows you to have multiple virtual networks by utilizing a single set of routers and links provided by the physical topology. Routers and links can be broken down into separate virtual networks using separate routing tables and routing processes by using vNETs and VRF configuration commands.
The virtual networks facilitate traffic isolation and limited fate sharing. The vNET feature supports command inheritance that allows commands entered in interface configuration mode to be inherited by every vNET configured on that interface. Use the vrf forwarding command to associate the edge interface with a VRF.
Use the vnet trunk command to enable a core interface. In the configuration hierarchy, a specific vNET interface setting has precedence over settings applied to the entire interface and inherited by each vNET configured on that interface.
CISCO EIGRP COMMAND AND CONFIGURATION HANDBOOK PDF
JoJomuro Austin configure terminal Moves to global configuration mode. See All Related Articles. Router config-router network Router config-router distribute-list 1 in. Austin config-if ip authentication key-chain eigrp susannah. The topology consists of four routers and some of you may have noticed that the topology is the same that we used for multi-area OSPFv3 configuration earlier in the chapter, and also uses identical IPv6 addressing scheme. The IPv6 routing table of R1 displayed above has several subnets, but two of them are highlighted.
IP Routing: EIGRP Configuration Guide, Cisco IOS Release 15M&T
Routing Command Reference for Cisco NCS 6000 Series Routers
Key Configurations on EIGRP
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