Best route selection process

Posted: February 13, 2016 in Routing

How best route is selected when there are multiple route available for same destination

1. Longest prefix match (more specific route)

e.g. destination is 10.10.10.10 and route available are
10.10.10.10/32 nexthop Se1/0
10.10.10.0/24 nexthop Se1/1
in this case route via nexthop Se1/0 will be preferred
2. Compare AD value (lower AD value is better)

3. Compare the metric (lower metric is better)

if AD is same and route is learned via same routing protocol then
selection is done by comparing metric.
4. Compare routing protocol preference

(AD value is same and but route are learned via different routing protocol)
connected > static > BGP > eigrp > ospf > isis


e.g. First condition if we have route 10.10.10.0/24 learned via ospf (110)and eigrp(90) (AD value is not modified for both protocol) route via eigrp will be selected


Second condition if we have route 10.10.10.0/24 learned via ospf (90)and eigrp(90) (AD value is modified for ospf and its equal to eigrp AD value 90) still route via eigrp will be preferred based on predefined routing protocol preference

Third condition if we have route 10.10.10.0/24 learned via ospf (89)and eigrp(90) (AD value is modified for ospf and its less than eigrp AD value) route via ospf will be selected based on lowest AD value

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s