Failover how much complexity will it add?

Seth Mattinen sethm at
Sun Nov 8 17:23:53 UTC 2009

adel at wrote:
> HI,
> I was recently brought onto a project where some failover is desired, but I think that the number of connections provisioned is excessive.  Also hoping to get some guidance with regards to how well I can get the failover to actually work.  So currently 4 X 100Mb/s Internet connections have been provisioned.  One is to be used for general Internet, out of the organisation, it also terminates VPNs from remote sites belonging to the organisation and some publicly accessible servers -routed DMZ and translated IPs.  Second Internet connection to be used for a separate system which has a site-to-site VPN to a third party support vendor.  Internet connections 3 and 4 are currently thought of as providing backups for one and two.  Both connections firewalled by a Juniper SSG of some description.
> Now I couldn't get any good answers as to why Internet connections 1 and 2 need to be separate.  I think the idea was to make sure that there was enough bandwidth for the third party support VPN.  I feel that I can consolidate this into one connection and just use rate limiting to reserve some portion of the bandwidth on the connection and this should be fine.  Now if I was to do this then I can make a case for just having one backup Internet connection.  However I'm still concerned about failover and reliability issues.  So my questions regarding this are:
> - Should I make sure that the backup Internet connection is from a separate provider?
> - How can I acheive a failover which doesn't require me to change all the remote VPN endpoints in case of a failover?  Its possible to configure failover VPNs on the Junipers, which should take care of this, but how do I take care of the DMZ hosts and external translation?
> - In fact I think I'm asking what are my options with regard to failover between one Internet connection and the other?

Forget all of that and just multihome to two separate providers with
BGP. Also make sure that of the providers you choose that one is not a
customer of the other. Instant, painless redundancy. Having multiple
circuits to one provider *will not* back anything up if that provider
has an outage as they are %99.999 likely to be part of the same larger
circuit and certainly share the same infrastructure at the provider.

> I'm hoping to figure out whether adding an extra Internet connection actually gives us that much, in fact whether it justifies the complexity and spend.

Only if you calculate the cost (money, time, angry customers, etc.) of
an outage to be greater than the cost of additional connectivity.

> Many Thanks for your comments.


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