[c-nsp] Simple NAT based IOS failover between providers

[Rodney Dunn]

Setup your NAT with route-maps to match on interface.
Depending on which interface the traffic is routed out
of will govern which interface your traffic gets nat'ed
to (ie: overload or pool) specific to that ISP.

Then you implement a way to make the route failover via
IP SLA (previously called SAA) to float your static route
from being up on the primary to switching over to the backup.

If the IP SLA object comes back the primary route will come
back in and your NAT will follow.

The gotcha I think with this is that any existing flow that
is being NAT'ed will fail until it times out because
a new translation on the new interface will have to be created.

Rodney


On Mon, Sep 26, 2005 at 11:01:37AM -0400, Robert Boyle wrote:
> 
> Hello,
> 
> We opened a ticket with the TAC and were told this was not possible. I 
> don't believe it. Many $79 generic Asian routers sold at office supply 
> stores can do this out of the box so I have to believe that Cisco with 10+ 
> years of IOS development and a $1500 router can do something this simple. 
> Situation details below:
> 
> Router with two "outside" interfaces - Both Ethernet in the cheap routers 
> or WIC-1DSU-T1 and WIC-1ADSL in our Cisco example
> Router has one "inside" Ethernet interface which runs NAT with IPSEC 
> passthrough.
> 
> The first outside interface is connected to ISP A (us in this case)
> The other outside interface is connected to ISP B (the local telco or cable 
> company in this case)
> 
> The router is configured so ISP A is the primary Internet link and it pings 
> the far side of the WAN connection to determine if the link is up. When the 
> primary link is up, all traffic is NAT mapped and sourced from the primary 
> WAN IP. If the ping fails, the router changes the NAT mappings to use the 
> second link with ISP B and all packets after that point are sourced from 
> the second WAN interface IP address. Fail back can be automatic after a 
> timer expires or a manual process such as a reboot. I don't really care 
> either way, but I do need the failover from ISP A to ISP B to be automatic 
> based on interface state, ping, or some other reliable method. I have seen 
> some documentation for IOS which enables changing routes based on a ping 
> response, but how do I change the NAT mappings as well? A working real 
> config or a pointer to a cookbook example would be great! We have Cisco PIX 
> boxes doing IPSEC behind these 1721s and 28xx routers at these sites and 
> timers set to 1 minute on the PIXes so they will reconnect within a minute 
> if the primary link fails. I believe that there HAS to be a way to make a 
> Cisco IOS router do something that a $79 consumer router can do! Thanks in 
> advance for any assistance!
> 
> -Robert
> 
> Before anyone suggests another method such as BGP, that won't work. We 
> can't provide the secondary link to these locations since they are isolated 
> small offices in independent telephone territories or cable is the only 
> option as ISP B (and ISP B doesn't speak BGP.) Thanks!
> 
> 
> 
> Tellurian Networks - The Ultimate Internet Connection
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> 
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