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

[Ted Mittelstaedt]

Do you even understand how those cheap Asian routers do this?

I will tell you.  They are dependent on running PPPoE to both
providers.  If the PPPoE session drops to 1 provider they assume
that leg is down.

What your missing though is that this kind of link state tells you
NOTHING about real connectivity.

Suppose your primary provider loses HIS connectivity to the rest of
the world.

If you did your redundancy with BGP like a real ISP does, then you
would instantly see this and would stop routing through him.

But if all your looking at is link state to your provider then your link
to your provider could be up but his to the rest of the Internet be down,
and your $79 router isn't going to switch over.

The very best way to handle redundancy is to find a provider that
is multihomed to your POP, and then setup a primary and backup link to
him.  Then run a routing protocol like OSPF or some such to him.
I've done this with customers before using RIP, it's a bit tricky but
it does work, unlike your kludge your wanting to do.  And yes we
are multihomed into the POP that I do this out of.

Naturally your provider could have a power failure or some such
that takes him out.  But if he's a good provider he will have redundancy
within his own network that will prevent this from happening, and you
will have a direct line to his engineers in case it does.

Getting 2 different cut-rate providers and trying to do redundancy to
them is not as good as finding 1 good provider and doing redundancy to
him.

Ted

>-----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 8:02 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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