Cisco CCNP 642-901 BSCI Exam Tutorial: EIGRP Adjacencies And Secondary Addresses Computers Articles | January 11 Black John Elway Jersey , 2007
In contrast to what some CCNP documentation states, you can form an EIGRP adjacency with secondary addresses - but you have to be careful! Learn the details from Chris Bryant, CCIE #12933.
I've read some non-Cisco documentation that EIGRP will not allow adjacencies to form when secondary addresses are used. This is incorrect, but there is one common error that can result if both addresses are not secondary. To fully prepare for the 642-901 BSCI exam Dre'Mont Jones Jersey , you should know about this error. Let's take a look at R2 and R3, which will be using secondary addresses to form an EIGRP adjacency across an ethernet segment.
Here's the partial output of show ip eigrp neighbor on R3:
R3#show ip eigrp neighbor
IP-EIGRP neighbors for process 100
H Address Interface
0 172.12.23.2 Et0
The adjacency has formed! Note the address is actually the primary IP address on the interface, even though we used the secondary network number in the EIGRP network command. Personally, I stay away from secondary network numbers if at all possible Drew Lock Jersey , but you should know that secondary IP addresses can be used to create EIGRP adjacencies.
What's the common error with using secondary addresses, you asked? It's when an address from the same subnet is the primary interface address on one neighbor and the secondary interface address on another. Let's say we had configured R2 and R3 as follows:
01:54:05: IP-EIGRP: Neighbor 172.12.23.3 not on common subnet for Ethernet0 (23.23.23.2 255.255.255.0)
Since we configured 23.23.23.2 as a primary interface address on R2, the EIGRP process is looking at the primary interface address on potential neighbors. R3's primary ethernet0 address is 172.12.23.2 Dalton Risner Jersey , so you get the "not on common subnet" error message - and what you don't get is an adjacency! That's something to be aware of on your 642-901 BSCI exam as well as when working with EIGRP in production networks.
Rote-Laterne-Roman
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20.08.2019 11:44
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