to a dns-server through two Routers with different subnet

[keeran]

Hallo.

I have the following network. I have already set the red router, sothat i can reach the google-server from all of my network(DMZ, LAN & Public). Now i am trying to simulate a backup ISP(the green router). The aim is to be able to ping bthe google server even if the ISP 1(the red) is down. I need to have the google server fa0/0 of red network and fa0/0 of green network in the same subnet. How do i configure static route on my intern router(the third router at the bottom) ?

[Giuseppe Larosa · Accepted solution]

Hello @keeran ,

first of all you need a larger target subnet as 8.8.8.8/30 allows for only two hosts.

At least you need

8.8.8.8/29

on the bottom router you will have

ip route 8.8.8.8 255.255.255.248 10.0.10.11

and a floating static route ( with an higher Admin distance ) via the backup router/ISP

ip route 8.8.8.8 255.255.255.248 10.0.20.11  220

in real world you could use either an IP SLA or a routing protocol like eBGP to check the primary path.

Hope to help

Giuseppe

[keeran]

just to make sure I understand correctly, so in your command "ip route 8.8.8.8 255.255.255.248 10.0.20.11  220" the 220 means: my router will normally send the google Traffic to the Router ISP1(10.0.10.9). Onyl if the ISP 1 Router isn't available for some reason, my router will decide to send the google traffic to the ISP 2(10.0.20.9). Is it right ?

[paul driver]

Hello
conditional ip sla static default routing  -

The example below will allow default routing to take isp1 path and if that fails in relation to ip sla monitoring  then the isp2 path will take precedence

your rtr

ip sla 1

icmp-echo 8.8.8.9 source- interface fa4/0

ip sla scheduled 1 start-time now life forever

track 10 rtr 1 reachability 

ip route 0.0.0.0 0.0.0.0 fa4/0 10.0.10.9 track 10

ip route 0.0.0.0 0.0.0.0 fa6/0 10.0.20.9 200