Using BGP for Disaster Recovery

[robertsturt]

Hi All,

We're considering using BGP for a DR solution. 

So, we have a provider independent /23 range which is currently assigned and in use in Telehouse, Docklands UK via Global Crossing Internet.  We'd like to install a new circuit from Virgin Internet in Farnham (also in the UK)  to be used in the event of a disater occuring - i.e. for whatever reason, the servers in Docklands cannot be accessed. The servers in Farnham replicate with Docklands but not real time, slightly behind and are not live unless we configure them to become live - i.e. a disaster occurs.  We therefore appreciate there's going to be some downtime for this to all take place.

So, in the event Docklands fails, we'd like to manually ask Virgin to advertise the /23 out using BGP - we can procure an AS number if required to go along side the /23 PI range.

The question is, how long it will take for the rest of the Internet to know that the /23 is now available via Virgin into Farnham rather than via Global Crossing in Docklands?

Hope this makes sense, Robert.

[Amit Aneja]

Robert,

If I understood you correctly, your question is that if you bring down the connection to Docklands & have Virgin advertise the same /23 subnet, then how long will it take for rest of the internet to change their BGP table & point towards Virgin.

I don't think that anybody can give you an exact time on when the routers on internet would change their BGP table to point to Virgin. There are lot of factors involved.

If you advertise the subnet via both ISPs, then you would need to do some kind of AS prepending to make sure that the route through virgin is preferred, so that you can test it & then later on prepend the path that you want to use as the backup path.

Regards,

Amit

[robertsturt]

Thanks for the reply.  We wanted to do this as a DR style of solution where we manually advertise the /23 out of Farnham.  I appreciate we could use AS path prepend to make the Farnham route less preferred but there;s still a chance of aysmetric routing.

So, yeah, the question is, how long (rough idea) does BGP take to update on the Internet?

[Amit Aneja]

Honestly, can't give you a number as this would depend on a lot of factors. 15-30 mins should be good enough time. Once you do it, you might want to check into the looking glass of various ISP & see if thye point at Virgin or not.

[argnetworking]

Big providers do it fast, in a couple of minutes the change is out.

In my experience, when I change an advertisement, it takes from 2 to 7 minutes to be replicated around the world. For small providers, it depends and you never know.