Static Routes Clarifications

[fkseow]

Hi I have two 2610 routers in one same office;

RouterA : S0/0.1 - 202.178.74.98 255.255.255.252 --------202.178.74.97

E0/0 - 172.16.132.1 255.255.254.0

Loopback0 - 202.178.79.37 255.255.255.0

Dialer0 - ip unnumbered loopback0

RouterB : s0/0 - 202.187.92.74 255.255.255.252-------202.187.92.73

e0/0 - 210.187.96.1 255.255.255.240

- 172.16.132.2 255.255.254.0 secondary

Static Route Of RouterA :

LA1 - ip route 0.0.0.0 0.0.0.0 172.16.132.2

LA2 - ip route 0.0.0.0 0.0.0.0 Dialer0 100

LA3 - ip route 172.16.0.0 255.255.0.0 Serial0/0.1

LA4 - ip route 172.16.0.0 255.255.0.0 Dialer0 100

LA5 - ip route 202.178.10.16 255.255.255.240 202.178.74.97

(1) Please clarify the difference between LA1 & LA3

(2) Please clarify the difference betweent LA2 & LA4

(3) When to use LA1,LA2,LA3,LA4 & LA5 ( Please confirm the sequence) ?

Static Route of RouterB :

LB1 - ip route 0.0.0.0 0.0.0.0 210.187.92.73

LB2 - ip route 172.16.0.0 255.255.0.0 172.16.132.1

LB3 - ip route 210.187.92.0 255.255.255.0 210.187.92.73

(1) Please clarify the difference between LB1 & LB2.

Note: All client workstations are of default-gateway to 172.16.132.1

[steve.barlow]

RouterA

1. la1 is your default route, if your router has no destination route in it's table, the packet will get sent to 172.16.132.2. La3 says that for packets destined for only 172.16.0.0 send it out interface s0/0.1.

2. La2 - This acts as your backup default route in case 172.16.132.2 drops. If the router's e0/0 drops, it will send packets (for which you have no routes) out your dialer interface. It is your backup as indicated by the 100 (you changed the admin distance from a default static route of 1 to 100) at the end of the line. La4 is your backup route to 172.16.0.0, as indicated by the 100 at the end of the line.

3. Sequence of the routes in your config doesn't matter. Route selection is based on most specific first (subnet mask/prefix - Longer prefixes are always preferred over shorter ones when forwarding a packet), then admin distance (http://www.cisco.com/warp/public/105/admin_distance.html), then the metrics of the route.

Routerb

1. lb1 - The default route again, without it packets with destinations not in your routing table would get dropped. Lb2 sends packets for 172.16.0.0 to 172.16.132.1.

To help clarify see these link: http://www.cisco.com/warp/public/105/21.html

Steve