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New Member

using different ip blocks from differnt ISPs

i have a problem :

i have a internet link from an ISP with 3 bits mask and first two octets are(195.133.xxx.xxx) when i get second internet link from a differrent isp with 4 bits mask and first two octets are 195.214.xxx.xxx , and my all equipments have first isp 's ip block. I want to use floating static routes for failover.

my question is :

when a link goes down , a second link from different isp will work ? or refused all my packets due to different ip block ? i am using 2610.

Best Regards

1 REPLY
New Member

Re: using different ip blocks from differnt ISPs

I'm going to assume that you have a single site, with two circuits terminating there.

Are you concerned with outbound traffic or inbound? If it's just outbound, then yes, floating statics will work. I would run HSRP (Hot Standby Router Protocol) between your two routers, and set your workstations' gateway address to the floating address(s).

With subnets that large, however, I'm guessing that you have a server or two that need to get inbound traffic. That's where this gets tricky. The problem is that the two ISPs won't (or shouldn't) route each other's addresses. So, if your DNS entry for a web server is 195.133.xxx.x80, and that link fails, there is not an easy way to adjust that DNS entry to 195.214.xxx.x80.

The best bet here, one that would provide the highest availability, is to register a block of IP addresses and a BGP (Border Gateway Protocol) AS (Autonomous System) number, independent of either ISP. You will need to get your ISPs to agree to accept BGP from you. In this configuration, you would have a link to ISP1 and ISP2, and configure your gateway routers to advertise your registered subnet to the world. All of your equipment would need to be migrated to the new subnet, but it could (and should) be behind a firewall, probably running NAT (Network Address Translation).

With this configuration, the world would get advertisements from your routers for your subnet. If one of the circuits fails, BGP will take over and select the valid remaining route.

HTH!

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