Q. EIGRP, OSPF, RIPV2 and routing table?

yrwins

i have a question.

a router has lear 3 posible routes that could be used to reach a destination on the network.
EIGRP metric of 20514560, RIPV2 metric of 4 and OSPF metric of 782.

why there is only EIGRP on the routing table.?

anfearr

If EIGRP has a longer prefix match than the other two it will be added, if it's equal it comes down to Administrative Distance, EIGRP is 90, OSPF 110 and RIP 120 so EIGRP wins. Only the routing protocol cares about the actual metric. This is different from the IOS selecting which route to put into the routing table as it will only enter the best route into the routing table which it decides by either prefix length followed by Administrative Distance which is basically how trustworthy the routing protocols are. In your case it believes EIGRP over OSPR or RIP.

yrwins

Anfearr. thanks...

anfearr

Just on futher point of clarification, In my reply I said it will add the most exact prefix (longest match) but it will actually also add one of the two remaining prefixes as it does not consider them the same unless they are 100% the same in which case it down to the AD.

james43026

Routing table selection process if a subnet has multiple choices, AD is checked first, if they are the same then the metric is checked. As Anfearr said, they would need to be the exact same network, otherwise they are considered to different routes / subnets.

pinkiaiii

guess also worth mentioning that eigrp summary route has AD of 5 .
anyways heres table of most protocols.

Connected = 0 AD
Static = 1 AD
EIGRP summary route = 5 AD
EXTERNAL BGP = 20 AD
Internal EIGRP = 90 AD
IGRP = 100 AD
OSPF = 110 AD
IS-IS = 115 AD
RIP = 120 AD
EXTERNAL EIGRP = 170 AD
INTERNAL BGP = 200 AD