routing tables

ilyas001 · October 30, 2016

hi guys if we take this example D 10.1.1.1/24 [90/123456] ........ (i know it's not finished but i just need to understand what's between [])

and also we got C 10.1.1.1/24 [120/2]

well guys the first number between [] and what's it's use also i don't get the first letters also what are they used for ?

Lurick · October 30, 2016

The number is the administrative distance, it tells the router which route to install and the lower the number the more preferable it is. The second number is the routing metric so if two routes tie on administrative distance then the metric is used to determine which is the better route to install.

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2

ilyas001 · October 30, 2016

2 hours ago, Lurick said:

The number is the administrative distance, it tells the router which route to install and the lower the number the more preferable it is. The second number is the routing metric so if two routes tie on administrative distance then the metric is used to determine which is the better route to install.

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2

thanks but sometimes the first number referse to protocols like it's said here

also the secound number sometimes is writen with a number like 123456 that's a hell of a big number i don't think this is a normal use that's why i ask cause we jump from 2 routers away to millions , is this normal ? or just for the sack of the example ? or possible but highly unlikely ?

Lurick · October 30, 2016

Yes, each routing protocol has a different administrative distance. For example the default AD for EIGRP is 90, you can also change the AD of a protocol to something higher or lower. The second number is a metric, not hop count. RIP uses hop count as it's metric but EIGRP, OSPF, and others use a formula to calculate their metric.