i have follow ing situation,
1.I have two different ISP and Two different public ip.
2.I have One cisco 1841 router and the router connected to ASA.
3.Nat is happening in ASA.
4.SMTP,WEB servers are nated in primary ISP IP.
Now i want to make high availablity network, if one ISP link is down second ISP will up and my servers accessible from outside. i need some sugestion
please find below diagram for reference.
Let me try and simplfy my previous explanation
Basically if you are going to have a primary shadow relationship between two ISP's you will need to get a BGP ASN as well as an network that would be honored, meaning routed by the secondary ISP. If your primary ISP cannot provide you enough address space to be routed by your secondary ISP then you will need to go to your Internet Registry and request a block of IPs that will be sizable enough to be routed by the secondary ISP. Other wise Dynamic DNS and static routing is your likely fall back.
Hope thats a little clearer.