does anyone use anycast

We run anycast DNS servers, currently as a pilot but we'll extend it in due course. The best description I could find is a presentation rather than a document - - but it describes what you need to do pretty well. The query-source command given on slides 49 and 50 seems to be superfluous, though.

The Cisco relevance is that you need to run a suitable routing protocol on your nameservers to propagate the anycast address. VRRP would only be relevant when you have the devices on a single subnet/VLAN.

Sam

Thanks a lot, I'll check out the link.

Mike

Thinking about the second part of your question, anycast/VRRP is probably not relevant for DHCP servers. If you want multiple servers on the same subnet/VLAN as the clients then there's no need because the clients just broadcast for whatever's there; if the servers are distributed across multiple subnets then you configure your routers with helper addresses to forward those broadcasts to wherever your servers are.

Sam

In my situation it won't work since there are multiple DHCP servers, only one per group, that administered by different departments. best not to confuse the issue. If there was one and a synchronized redundant that would be another matter.

Mike

If that's the case, then anycast wouldn't help you anyway. You have come up with the solution on your own. Don't let politics get in your way. If you have a good solution and can articulate the benefits to the departments your

90% there. Find one department that is willing, and then another, and another. After a while you will have critical mass to make it an IT policy that will bring the departments that think that controlling the DHCP server is their own little fiefdom.

Scott

It also depends on what DHCP is used for. It's much easier to back up a DHCP service which is handing out static addresses to known MAC addresses than to coordinate dynamic pools across multiple servers.

Sam

Actually my intent was to apply that to DNS only. From what I've seen there is no truly redundant and synchronized DHCP system available. Unless someone has experience with some DHCP system that is?

Mike

Let me repeat - it depends on what DHCP is being used for. If you're using it for dynamic allocation from a pool then you're right - it's difficult to have redundancy. If you're using it for static allocation, i.e. easier maintenance of address assignment, then it's fine you can have as many servers as you want backing each other up.

Sam

it is difficult to have redundancy from 1 DHCP pool, but in many cases you can throw extra address space at the problem if you dont care too much exactly which adr goes where.

2 DHCP servers are each given half the address pool on each subnet. whenever a request comes in, the end station is offered 2 addresses, 1 from each server. if there is a fault, then only half the addresses can be offered, so you need double the number of addresses across the 2 pools than might be needed without the dual servers.

what you lose is you double the address space of each subnet, but keep the same number of DHCP clients you get more background broadcasts

If you're using it for static allocation,