Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

This is the situation I've inherited: There are two routers, one off-site. Both are connected to the ISP. The ISP assigns both of them the same static IP (or so it seems). Presumably, the network problems we're having are related to the idea that you can't have two instances of the same IP.

So we rang up the folk off-site and told them to turn off the router. Now everything's working okay here.

How do I get around this? Get another static IP? Figure out how to get the router to ask for a dynamic IP (as we're not using the static IP for anything)?

share|improve this question
add comment

2 Answers 2

up vote 1 down vote accepted

This does not work - two routers with the same IP in the same ISP network would not be something to keep apart, unless the router is only in a pass through scenario - and then the "one off site" means to me they are not replacable (as you have cross traffic if a packet goes to the wrong side). While it may be workable - depends on the network layout - I would NOT want that. You will need another IP for the off site router. Ask your ISP. Dynamic strongly preferred if nothing is done with the static one anyway.

share|improve this answer
add comment

This could be done for redundancy if the two routers are in different geographic locations and the ISP is advertising the IP for you. This is often referred to as anycast, and can cause problems with TCP traffic.

However, if you don't know that this is going on, than it probably isn't intentional :-)

Another possibility is that there is redundancy in the same location with some sort of VIP (Virtual IP) setup such as HSRP. In this only one router at a time should hold this virtual IP, however, if things have gone wrong they both might hold it (Creating split-brain scenerio or a network partition, whatever you want to call it). Although this doesn't quite make sense to me if the ISP really is assigning the IP.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.