EIGRP is an major part of the pack of real-world networking as fit as person a through substance on the 642-901 CCNP BSCI exam. As near any networking topic, back you try to master grey and advanced skills, you essential maestro the basics. It doesn't get any much major than the EIGRP closeness activity - 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 occupation beside R1 and R2, two Cisco routers communicating complete a serial interface. EIGRP is once running on R2's successive interface, but was fair enabled on R1's serial interface. The EIGRP contiguousness procedure begins beside R1 causation an EIGRP Hello parcel to the multicast address 224.0.0.10 in an seek to find eventual neighbors.
R2 will have this Hello parcel and respond with a Hello collection as powerfully as an EIGRP Update collection. This parcel will enclose all the EIGRP routes R2 knows of, as drawn-out as the guidelines of tear apparent horizon is not profaned. (Split horizon dictates that a line cannot be publicized out the said interface that has acceptable an personal ad for that selfsame trail.)
Oddly enough, the EIGRP Update assemblage 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 firstborn chemical phenomenon of routes next to a new neighbor, the Update assemblage is unicast.
In response, R1 will dispatch an EIGRP ACK, stumpy for acceptance. That lets R2 cognise that R1 received the EIGRP routes. R1 will also direct an unicast Update collection to R2, which R2 will hold.
A primary quality concerning EIGRP and OSPF adjacencies is that EIGRP speakers do not have to concur on hello and cold times, wherever an OSPF contiguity will never gel relating routers exploitation assorted howdy and d.o.a. modern world. However, EIGRP speakers essential concur on the Autonomous System (AS) figure as all right as the metric linear unit weight values. We have an contiguity betwixt R1 and R2, but what happens to that contiguity if the metric weights are denatured 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 manoeuvre 100
R2# (Nothing to see here!)
The closeness is worn down! If we denaturised the metric weights on R1 or separate that past plan from R2, the nearness would come rear up. You should have a highly biddable apology to devolution the EIGRP metric linear unit weights in the early place, but if you do tweaking them on one EIGRP utterer in an AS, you improved do so on all the separate speakers in the AS as cured. And if you do so, corroborate them next to show signs of ip eigrp neighbor!