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NAT and Routed Network with Two ISP's on one router

I'm sure this has been done covered many times, but I am not finding it.


I have two ISP connections.

With ISP-A I have a /30 between us and is routed to me via the /30 for thsi example we will say the /30 is on isp end and on my end


With ISP-B I have a subnet. and the ISP gateway is on that subnet at


On the inside of my network I have devices using both 200.100.100.x addresses and devices on 192.168.100.x that need to use NAT.

I would like all of the devices on 200.100.100.x addresses to continue using ISP-A as their gateway.

Everything on 192.168.100.x should use NAT and go out ISP-B


I have tried

ip nat inside source route-map ISP-A interface GigabitEthernet0/1 overload

route-map ISP-B permit 10
 match ip address 101
 match interface GigabitEthernet0/1
 set ip next-hop
route-map ISP-A permit 10
 match ip address 111
 match interface Multilink1
 set ip next-hop

The problem comes when I have default routes to ISP-A in the router than none of the ISP-B traffic works, and vice versa.

  • LAN Switching and Routing
VIP Super Bronze

I think for this to work

I think for this to work correctly and be able to split traffic between the 2 ISPs, you would need to use BGP, because default is going to use one ISP or the other.

If you can use BGP, this link will help you in load shearing between multiple ISPs when you have one router.


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