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

[Chris Moore]

Just as a "general architecture" comment:

First, understand exactly what you are trying to do. For outgoing
traffic, it's really easy. You just have two default routes out two
public interface and tell them both to NAT. Use route metrics to
determine primary/secondary. That's what your $79 consumer router is
doing. Really simple.

Incoming traffic is a different story. Sure - it's easy enough to have
two NATing interfaces and just have two sets of NAT mappings. But how
does "the world" know to go to the other set of addresses? You need DNS
for that. SO that means doing your own DNS or working with someone who
will let you run scripts to do DNS updates. Then have a script that goes
out and changes DNS when one of the links goes down. The script is
pretty simple - you should be able to find plenty of examples online.
Some ISPs and other companies (DynDNS.org comes to mind) offer managed
functionality like this.

Chris  

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Robert Boyle
Sent: Monday, September 26, 2005 9:02 AM
To: cisco-nsp
Subject: [c-nsp] Simple NAT based IOS failover between providers


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
http://www.tellurian.com | 888-TELLURIAN | 973-300-9211 "Well done is
better than well said." - Benjamin Franklin

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