EIGRP is an exalted component of real-world networking as good as man a prima theme on the 642-901 CCNP BSCI examination. As next to any networking topic, in the past you try to artist third-year and precocious skills, you essential artist the bedrock. It doesn't get any much basic than the EIGRP adjacency route - and it doesn't get any much important, because in need that adjacency, we don't have an EIGRP deployment!
In today's CCNP tutorial, we'll sweat next to R1 and R2, two Cisco routers human action finished a consecutive surface. EIGRP is at one time moving on R2's serial interface, but was honorable enabled on R1's sequential surface. The EIGRP adjacency route begins with R1 causation an EIGRP Hello accumulation to the multicast computer address 224.0.0.10 in an have a go to brainstorm potential neighbors.
R2 will receive this Hello package and retort with a Hello aggregation as healed as an EIGRP Update bundle. This bundle will encompass all the EIGRP routes R2 knows of, as daylong as the course of action of separate apparent horizon is not violated. (Split horizon dictates that a trail cannot be advertised out the aforesaid surface that has prescriptive an promotion for that selfsame itinerary.)
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Oddly enough, the EIGRP Update aggregation sent by R2 will be a unicast packet, not a multicast. EIGRP Update packets are mostly multicast to 224.0.0.10, but during the original switch over of routes next to a new neighbor, the Update package is unicast.
In response, R1 will convey an EIGRP ACK, pithy for recognition. That lets R2 cognize that R1 received the EIGRP routes. R1 will too send an unicast Update accumulation to R2, which R2 will declare.
A crucial peculiarity involving EIGRP and OSPF adjacencies is that EIGRP speakers do not have to concord on how-do-you-do and fallen times, where on earth an OSPF adjacency will ne'er silhouette betwixt routers using divergent hello and stillborn nowadays. However, EIGRP speakers must hold on the Autonomous System (AS) amount as healthy as the metrical weight belief. We have an contiguousness betwixt R1 and R2, but what happens to that contiguity if the metric weights are denaturised on R2?
R2(config)#router eigrp 100
R2(config-router)#metric weights 0 1 1 1 1 1
R2#show ip eigrp neighbor
IP-EIGRP neighbors for method 100
R2# (Nothing to see here!)
The nearness is torn down! If we transformed the metrical weights on R1 or separate that end plan from R2, the adjacency would travel wager on up. You should have a completely favorable judgment to loose change the EIGRP metrical weights in the early place, but if you do transfer them on one EIGRP mediator in an AS, you improved do so on all the new speakers in the AS as in good health. And if you do so, affirm them near be evidence of ip eigrp neighbor!
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