Multihoming Suggestions w/o at Least a /24?

An anonymous reader asks: "I work for a small company who is looking to get a multihomed Internet connection for redundancy. The logical conclusion would be to get another internet connection to another provider. However, in the case of a primary connection failure, we need to be running BGP to have our internally-hosted sites still accessible to the Internet via the 2nd connection. The problem is that we only have a /28 (16 IPs), which is too small to make it past most route filters, and would then mean that we still couldn't be reached if the primary T1 is down. So, what's our options? (and no, lying and getting a /24 isn't a valid choice)"

Comments

It depends on the services...

[amorsen]

The obvious choice is to get a second set of 16 addresses on the other connection, and then make your DNS server send out addresses to whichever connection currently works. Not all services like switching addresses, and sessions break when doing failover, but it might work for you. If you only care about outgoing traffic, load-balancing and failover is fairly easy to do and there are lots of products to help. Again, outgoing sessions will get killed if they happen to use the link that breaks.

Re:It depends on the services...

[photon317]

Yeah outbound traffic is easy, it's the inbound he's having a problem with I'm sure. The problem with two sets of addresses and DNS switching is the caching. Even if you set your records to expire in 30 seconds or something crazy like that, at various levels the records *will* get cached much longer than that, and it will "problematic" at best.

This question is truly worthy of Ask Slashdot, which is a first in a long time. I have yet to see a good answer for someone who wanst truly redundant internet connectivity and has too small an address space to really do BGP peering.

I thought of one solution at the ISP end of things, which would require partnerships between ISPs. Two distinct competing ISPs could grab a decent-sized netblock and share it. They sell these IPs to customers wanting dual-homed access from both ISPs, and split the money. In this type of scenario the customer can BGP to both ISPs, who in turn BGP with each other and the real backbone, and you can get all the redundancy you need in case of ISP or wan-link failure.

Legal v.s. technical issues.

[pruneau]

Of course, the usual question is: what can you afford to have redundancy ?

Because before technical solutions, you might want to review the contract with your access provider to include liabilities. The contract itself might cost more, but it might be simpler than a real redundant solution.

Because unless you know for a fact than your access provider is not reliable and has bad support, playing the redundancy game might be a bit more expansive than "simply" getting a double connection from the internet.

Let's do the excercise: you want a dual internet connection, that's OK, but you surely do not want a single router=single point of failure. So you have to buy another router, most probably the same brand as the one you already have, so to be able to use the (most probably) proprietary high availability solution. Provided your current model supports HA, or you will have to buy a more expensive one ?

Which brings to mind that having a redundant link (with an SLA :-) from the same provider might be an excellent idea, since they are probably aggregating your /28 to other /subnet, your route advertisment won't get lost in their network until it gets aggregated. Just make sure it does not get aggregated on the next hop ;-) Well, if you are willing to pay for multi-homing, woul'dt it be easier to try to obtain an SLA with only one access provider, SLA including an redundant routing connection, with some redundancy protocol handled