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New Member

ISP Redundancy

I have a PIX 515 which is used as a firewall and VPN hub.

At present each of the remote sites connect, via a VPN tunnel, to this PIX via the single ISP connection.

To provide a level of redundancy, at the ISP level, I wish to get a link from a second ISP. Is it possible to establish two tunnels from the remote sites, both of which terminate on the same PIX (at head office) but connect via the different ISPs.

I am guessing that I would have to use a routing protocol over the tunnels to allow for the traffic to switch between the primary and secondary tunnels as the ISP links go up and down.

Ideally to provide for full redundancy I should use two PIX's and terminate the one ISP and tunnel on each. However at this point I would like to get by using just one PIX.

If this is possible is there any documentation on how this is done?

I appreciate your input into this matter


New Member

Re: ISP Redundancy

The quick answer is that "the pix is not a router" so it can't make routing decisions about which ISP to send the data to. No matter how you get traffic to the Pix, it's only going to send traffic back to the internet via one default gateway, which means all return traffic will have to go out via whichever ISP's router is set as your default route.

Putting in two pixes wouldn't help too much either, because your internal clients would only have one default route: 1 pix or the other.

A high-end approach to this would be to buy a block of public IP addresses and then do BGP peering with two ISPs....but this probably isn't appropriate for your scenario.

However, a less-intensive way around this would be to place a router between the Pix's outside interfaces and the two ISP routers. This router could the using policy routing to set the next hop address based upon the source IP. This would then send return VPN traffic back via the correct ISP.

New Member

Re: ISP Redundancy

Hi Jeff, Thanks for you input.

This properly comes down to a basic router/firewall functionality issue, but just to get this clear in my mind.

If I have the PIX with two interfaces, E1 goes to ISP1 and E2 goes to ISP2, the default gateway for the PIX is out E1. An IPSec tunnel establishment request arrives via E2.

I gather from your reply, the PIX will send the reply to this request out E1 rather than out the interface the request came in on (E2)?

Under this scenario, will a tunnel actually be established? if so on what interface will the tunnel be established on?

I do understand that straight Internet traffic, i.e. web browser traffic, would stop flowing if ISP1 (E1) was to go down due to the default gateway not being accessiable.

Again thanks for your input


New Member

Re: ISP Redundancy

You can specify multiple VPN peers per crypto map which will renegotiate the VPN. You will only be able to use one link at a time.

"You can define multiple peers by using crypto maps to allow for redundancy. This configuration is also most useful for site-to-site VPNs. If one peer fails, there will still be a protected path. The peer that packets are actually sent to is determined by the last peer that the PIX Firewall heard from (received either traffic or a negotiation request from) for a given data flow. If the attempt fails with the first peer, IKE tries the next peer on the crypto map list."



Paul Dawson