Cisco Systems 3560 Manual De Usuario

Enhanced IGRP (EIGRP) is a Cisco proprietary enhanced version of the IGRP. EIGRP uses the same 
distance vector algorithm and distance information as IGRP; however, the convergence properties and 
the operating efficiency of EIGRP are significantly improved. 

The convergence technology employs an algorithm referred to as the Diffusing Update Algorithm 
(DUAL), which guarantees loop-free operation at every instant throughout a route computation and 
allows all devices involved in a topology change to synchronize at the same time. Routers that are not 
affected by topology changes are not involved in recomputations.

IP EIGRP provides increased network width. With RIP, the largest possible width of your network is 
15 hops. Because the EIGRP metric is large enough to support thousands of hops, the only barrier to 
expanding the network is the transport-layer hop counter. EIGRP increments the transport control field 
only when an IP packet has traversed 15 routers and the next hop to the destination was learned through 
EIGRP. When a RIP route is used as the next hop to the destination, the transport control field is 
incremented as usual. 

EIGRP offers these features: 

Fast convergence.

Incremental updates when the state of a destination changes, instead of sending the entire contents 
of the routing table, minimizing the bandwidth required for EIGRP packets. 

Less CPU usage because full update packets need not be processed each time they are received.

Protocol-independent neighbor discovery mechanism to learn about neighboring routers. 

Variable-length subnet masks (VLSMs).

Arbitrary route summarization.

EIGRP scales to large networks.

EIGRP has these four basic components: 

Neighbor discovery and recovery is the process that routers use to dynamically learn of other routers 
on their directly attached networks. Routers must also discover when their neighbors become 
unreachable or inoperative. Neighbor discovery and recovery is achieved with low overhead by 
periodically sending small hello packets. As long as hello packets are received, the Cisco IOS 
software can learn that a neighbor is alive and functioning. When this status is determined, the 
neighboring routers can exchange routing information.

The reliable transport protocol is responsible for guaranteed, ordered delivery of EIGRP packets to 
all neighbors. It supports intermixed transmission of multicast and unicast packets. Some EIGRP 
packets must be sent reliably, and others need not be. For efficiency, reliability is provided only 
when necessary. For example, on a multiaccess network that has multicast capabilities (such as 
Ethernet), it is not necessary to send hellos reliably to all neighbors individually. Therefore, EIGRP 
sends a single multicast hello with an indication in the packet informing the receivers that the packet 
need not be acknowledged. Other types of packets (such as updates) require acknowledgment, which 

show ip ospf neighbor [interface-name] [neighbor-id] detail

Display OSPF interface neighbor information.

Display OSPF-related virtual links information.