We have one 4331 cisco vpn router at a site, we are looking for a back up link to be installed from a different ISP provider, so we will have primary and back up internet links from 2 different providers. Can we configure both of these links on the existing 4331 router? Or is additional features needed such as a network card?
Usually in this case I would just order 2 routers as a dual set up with fail over. But I am just wondering if it is in fact possible to perform on one router?
Look like your using the ISP link to build the remote site VPN? And would like to study if you could utilize both ISP links to have a resilience purpose.
Indeed, if you have 2 WAN links, but centralized in 1 router. You still got the single point of failure at your router (even through you are paying for two of WAN links), you should evaluate if you / your company accept the risk or not.
First check if you router 4331 have enough Ethernet port to pick up, or actually you could implement "router on a stick" if you have no enough interfaces;
I assume both ISP links should use the different public IP address space, and you could consider to build 2 VPN tunnel over each ISP to your remote site. So that, the traffic passing through the 1st tunnel will utilize 1st ISP, and vice versa. After that, you may configure IP/SLA or running dynamic routing protocol to control the data traffic flowing to which tunnel. (e.g. when 1st tunnel is down, data should flowing through 2nd tunnel).
That's the idea, and below is the configuration reference for router choosing different ISP to build the VPN:
Assume: IP address of Your router's ISP A: A.A.A.A (ISP router/gateway: A.A.A.254) IP address of your router's ISP B: B.B.B.B (ISP router/gateway: B.B.B.254) remote site VPN gateway: C.C.C.C