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EIGRP is an critical a part of actual-worldwide networking similarly to being a primary concern depend at the 642-901 CCNP BSCI exam. As with any networking problem depend, earlier than you attempt to grasp intermediate and superior talents, you need to understand the basics. It may want to not get any greater essential than the EIGRP adjacency method - and it does no longer get any more crucial, because of the reality without that adjacency, we don't have an EIGRP deployment!

In present day CCNP instructional, we're going to art work with R1 and R2,  Cisco routers speakme over a serial interface. EIGRP is already strolling on R2's serial interface, however modified into simply enabled on R1's serial interface. The EIGRP adjacency device begins with R1 sending an EIGRP Hello packet to the multicast deal with 224.0.0.10 in an try to locate capacity pals.

R2 gets keep of this Hello packet and reply with a Hello packet further to an EIGRP Update packet. This packet will include all the EIGRP routes R2 is privy to of, as long as the rule of thumb of split horizon is not violated. (Split horizon dictates that a path can't be advertised out the identical interface that has obtained an advertisement for that same route.)

Oddly sufficient, the EIGRP Update packet transmitted with the resource of R2 could be a unicast packet, no longer a multicast. EIGRP Update packets are commonly multicast to 224.Zero.Zero.10, but in the path of the primary trade of routes with a brand new neighbor, the Update packet is unicast.

In reaction, R1 will ship an EIGRP ACK, brief for acknowledgement. That we need to R2 comprehend that R1 obtained the EIGRP routes. R1 may even ship an unicast Update packet to R2, which R2 will famend.

A essential distinction among EIGRP and OSPF adjacencies is that EIGRP audio device do no longer must agree on howdy and lifeless times, wherein an OSPF adjacency will by no means form amongst routers the use of truly one among a kind whats up and useless instances. However, EIGRP audio machine ought to agree on the Autonomous System (AS) amount in addition to the metric weight values. We have an adjacency between R1 and R2, but what takes place to that adjacency if the metric weights are changed on R2?

R2(config)#router eigrp a hundred

R2(config-router)#metric weights 0 1 1 1 1 1

R2#show ip eigrp neighbor

IP-EIGRP pals for gadget 100

R2# (Nothing to appearance proper right here!)

The adjacency is torn down! If we changed the metric weights on R1 or removed that final configuration from R2, the adjacency may come again up. You need to have a extremely good reason to alternate the EIGRP metric weights in the first place, but if you do exchange them on one EIGRP speaker in an AS, you better accomplish that on all the one of a kind audio gadget within the AS as nicely. And if to procure this, verify them with display ip eigrp neighbor!

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