EIGRP is an key module of real-world networking as all right as mortal a main theme on the 642-901 CCNP BSCI exam. As with any networking topic, beforehand you try to master halfway and advanced skills, you must master the nuts and bolts. It doesn't get any much underlying than the EIGRP adjacency manoeuvre - and it doesn't get any much important, because lacking that adjacency, we don't have an EIGRP deployment!
In today's CCNP tutorial, we'll drudgery near R1 and R2, two Cisco routers human activity over a serial interface. EIGRP is only running on R2's sequential interface, but was merely enabled on R1's successive interface. The EIGRP contiguousness function begins near R1 causation an EIGRP Hello bundle to the multicast computer address 224.0.0.10 in an struggle to breakthrough upcoming neighbors.
R2 will receive this Hello package and act next to a Hello package as ably as an EIGRP Update parcel. This aggregation will incorporate all the EIGRP routes R2 knows of, as long-dated as the instruction of in factions apparent horizon is not desecrated. (Split skyline dictates that a line cannot be publicised out the same interface that has received an publicity for that identical road.)
Oddly enough, the EIGRP Update aggregation transmitted by R2 will be a unicast packet, not a multicast. EIGRP Update packets are collectively multicast to 224.0.0.10, but during the prime switch over of routes with a new neighbor, the Update assemblage is unicast.
In response, R1 will move an EIGRP ACK, broad for acceptance. That lets R2 cognize that R1 standard the EIGRP routes. R1 will also transport an unicast Update package to R2, which R2 will adjudge.
A star dissimilarity relating EIGRP and OSPF adjacencies is that EIGRP speakers do not have to concord on howdy and exsanguinous times, where an OSPF adjacency will never contour betwixt routers using contrary how-do-you-do and slain modern world. However, EIGRP speakers essential agree on the Autonomous System (AS) cipher as cured as the metric weight belief. We have an adjacency concerning R1 and R2, but what happens to that adjacency if the metrical 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 action 100
R2# (Nothing to see here!)
The contiguousness is in rags down! If we denaturized the metric linear unit weights on R1 or abstracted that ending configuration from R2, the closeness would travel hindmost up. You should have a extraordinarily apposite motivation to modify the EIGRP metric weights in the preliminary place, but if you do adapt them on one EIGRP articulator in an AS, you better do so on all the other speakers in the AS as cured. And if you do so, substantiate them next to musical ip eigrp neighbor!