[c-nsp] multihoming solution over two different ISP's

Joe Maimon jmaimon at ttec.com
Mon Aug 8 09:46:03 EDT 2011

Get a 2950 or even a 3524XL, use vlans and subinterfaces.

Use BGP if available.

Otherwise, if you are already using NAT, then this should work fine.



If you need redundancy and incoming IP reachability, and you cannot get 
BGP/Public IP addresses from your existing ISP's, you can obtain it from 
other ISP's, even if all they can offer you is a tunnel.


Martin T wrote:
> At the moment I have a following setup:
> http://img69.imageshack.us/img69/4227/252530.png
> The ISP-A connection is the primary link and the ISP-B connection(over
> WiMAX) is the backup one. In case the primary link fails, I physically
> plug out the fiber-optical converter cable from my Cisco router(Cisco
> 1841) and insert the one from WiMAX device. In addition, I reconfigure
> the IP parameters in the router. This is probably the most manual
> "multihoming" possible :) I'm ready to upgrade my router so it
> supports two Ethernet cables.
> a) Is it somehow possible to automatically switch over to another one
> connection in case the primary one fails. For example ping
> www.google.com over a period of time and in case it doesn't respond,
> automatically switch over to backup connection?
> b) Is it somehow possible to have one static IP address while using
> the services of two different IPSs?
> While I'm afraid the latter is impossible, the first automatic
> switchover should be somehow doable, shouldn't it? As I told, I'm
> ready to invest into new equipment if it's necessary.
> PS I'm aware, that probably the most elegant solution would be a BGP
> sessions with ISP routers over different last-mile technologies. This
> would provide fast failover and I could use one IP address.
> What are the best practices for multihome connection over two different ISP's?
> regards,
> martin
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