Redundant Link

I have a client who has 2 servers on his premises.

He has a connection to a Cable provider who also gives him his IP addresses and now decided to take one our our wireless links to have redundancy.

He hosts his own DNS server and domains.

I cannot understand how we are going to give him any redundancy since when the Cable Internet connection is down, his IPs will cease to route and hence his servers will be unreachable on the Net.

Any ideas how we can help him in this?

BGP … -faq.shtml

Yep, i thought of that, but the client does not have a router or own his own set of IP addresses.

they are given to him by the Cable company.

It would not be true redundancy. It would require manual user interaction with the servers. In the event of his Cable connection failure, he would need to switch to his Canopy link, and modify his domain information.

More specifically, you would need to provide him with two (or however many) dedicated IP addresses on your block. When his Cable connection goes down, he would need to use his Canopy connection to login to the web interface that he uses from his domain registrar, and modify the authoritative name-server IP addresses for his domain(s). He would change the IP addresses from the ones provided by the cable company, to the ones that you provide with him. True propogation of this information can take (worst case) up to 24 hours, sometimes even more.

Depending on what type of records he has in his name server configuration files, those would need to be modified as well. For example, if an A-record for originally pointed to a static IP address on the Cable company’s block, that record would need to be changed to point to the new IP address (yours). This really wouldn’t be too difficult, he would just have to make a backup configuration file as well as backup configuration files for all the domains he provides records for, all containing the information relative to the new IP addresses.

Is it worth it, I don’t know. The biggest problem will be propogation time. Switching to backup config files isn’t a big deal, you could write a simple script to accomplish that.

Hope this helps. Keep us posted.

I think I would use it as an opportunity to make an extra 100 bucks a month by offering to colo his servers at my head end.

Your T1/DS3 or whatever you are using (not a DSL I hope) is more stable than the Wireless or Cable links, especially if you have an SLA with your ISP.

Then he could kill his cable connection and use you exclusively. You are the ISP with a name and a face…


Agree that the best solution would be colocation at your datacenter, but depending on the type of servers, maintaining reliable access from the customer’s office to the machines might be more important than maintaining access to the machines from the Internet.

BGP won’t work for redundant paths unless the customer has his own AS number registered with ARIN, and unless it’s a giant company with a /21 or bigger IP block then that probably won’t be happening. And since their primary connection is DSL…

I think the best option, although not really a truly redundant solution, would be DNS round robin load balancing between two IP addresses for each machine. Customer would maintain two NICs on each server, one connected to each provider. A script or OS-specific software system would determine when each interface has connectivity to the internet, and disable or enable the interfaces accordingly. DNS round robin would split incoming traffic between the two interfaces, so the probability of a generic internet user encountering a downed interface is lowered. By setting the DNS TTL low and manually removing downed entries from the round robin table an acceptable level of availability could be achieved.

Any other ideas?

i would use his dns as primary and use your dns as secondary and under the advanced section of the tcp/ip config i would add another ip string from your system the it should auto swap. or get a router with 2 wan inputs. or put in an extra 10/100 card and disable and enable as needed.

kenny meadows

Another way you could do it is to use a 2 wan port router like one xinicom, which would also let him load balance between the two connections. If he is hosting his DNS, set the primary address on the cable IP and secondary on the Wireless IP and put in a round robin on the DNS entrys, it would balance between the two connections. If one does go down, every other incoming connection would not work. I guess working half the time is better than not at all.

Thanks guys. We all seem to have come up with the same ideas…

Thanks again for your time.