Cisco Buffs, Cisco 881 - Can you configure 2 x WAN's, one on the Ethernet WAN port FE4 and a backup

DJMK4 · 10 Aug 2012 at 11:19

Hi all,

Just a quick question for the Cisco buffs, I am looking to use a Cisco 881 router with K9 firmware, ideally what we want to do is we have an ethernet circuit, which we are going to configure the dedicated FE4 WAN port on this cisco to manage, in addition, the customer has an ADSL circuit, which they want to use as a backup link, now this Cisco 881 doesnt have an ATM interfaces (ADSL interfaces) like you get on other routers, and no WIC slot.

Can we just stick an ADSL Modem on the BT line, have an ethernet link going in to one of the FE ports on this Cisco and configure it that way? so that when the Ethernet WAN goes down, the ADSL will take over?

Nunzio · 10 Aug 2012 at 13:24

Yes you can.

Either using dedicated vlans or routing with tracked routes.

DJMK4 · 10 Aug 2012 at 14:43

Do you have any example config? even some hints so what to search for on google (What its called this method) been trying to trawl through google but what I am finding I dont think is actually what I am looking for.

Been looking for stuff like dual wan, ethernet wan with adsl backup.

Dual Wan failover.

Devz · 10 Aug 2012 at 15:26

This might be of use to you or at least give you an idea of what a config might look like
http://docwiki.cisco.com/wiki/NAT_failover_with_DUAL_ISP_on_a_router_Configuration_Example

Trifid · 10 Aug 2012 at 15:30

10.9.0.1 = a loop back address
6.6.6.6 = any IP address on the internet that is reliable and responds to ping
10.2.0.1 = main internet connection interface IP address
10.0.0.0 = LAN IP address range

IP SLA 1
ICMP echo 6.6.6.6 source IP 10.9.0.1
frequency 1

ip sla schedule 1 start-time now life forever

track 1 ip sla 1 state
delay up 5 down 5

access-list 101 permit ip host 10.9.0.1 host 6.6.6.6
access-list 101 permit ip 10.0.0.0 0.0.0.255 any

route-map PBR permit 10
match ip address 101
set ip next-hop verify-avai 10.2.0.1 track 1

ip local policy PBR

int Fa0/0
desc LAN
ip policy route-map PBR

I think that's everything. I've not checked through it all though.

Edit: you'll need a ip route to the other WAN interface.

Or you could just add the tracking to the IP route to save all the route map stuff. Would be much easier actually. The route map would allow some load balancing by distinguishing between traffic types/source/destination etc.