I never bother with the 80-20 thing myself, if I have dual DHCP servers (which I like to) I always try to give each a large enough address pool to cover the entire network.
The rare exception is if I have too many devices for the subnet to be completely split like that - i.e. 175 devices on a Class C subnet. That's pretty rare, though, because if I have that many devices I've probably chosen an IP addressing scheme that can more readily accommodate them. I'm actually sort of fond of using Class B schemes (172.23.x.x) for example. Regarding #3 - when your client boots it only needs to check that it still has an IP address. If it's still within the lease period there's no need to rebroadcast. It either quietly goes on using the address it already has, or if it's at the proper time in the lease (50%) it'll send out a routine renew request to the issuing server. Most of the time it doesn't have to do anything. Ben M. Schorr Chief Executive Officer ______________________________________________ Roland Schorr & Tower www.rolandschorr.com b...@rolandschorr.com Twitter: http://www.twitter.com/bschorr -----Original Message----- From: Jim Dandy [mailto:jda...@asmail.ucdavis.edu] Sent: Friday, May 01, 2009 8:41 AM To: NT System Admin Issues Subject: RE: DHCP 80-20 rule I still don't get the 80-20 thing. 50-50 would distribute the load better and would potentially give you more leases if one fails. Perhaps the hope is that the one that fails is the one with 20% and that 80% would give you adequate addresses to be fully functional while you fix the 20. Thanks for the info on the no-broadcast for renewals. Here is another question ... 3) Let's say you reboot your client before the lease expires. On reboot does it do a broadcast to get a new address or does it just try to renew from the DHCP server from which it got its original lease? Curt > -----Original Message----- > From: Kennedy, Jim [mailto:kennedy...@elyriaschools.org] > Sent: Friday, May 01, 2009 11:17 AM > To: NT System Admin Issues > Subject: RE: DHCP 80-20 rule > > > > -----Original Message----- > > From: Jim Dandy > > > 1) Why 80-20? Why not 50-50? If one server fails, wouldn't it be > > better for the other server to have a larger range from which to > > distribute addresses? > > The 20 is designed to keep you alive and running while you fix the 80 server. > Certainly a full range on both servers to serve all your clients would be > great, if your subnetting and available addresses allow it. > > > > > 2) Let's say everything is working perfectly and both DHCP servers are > > up. Client1 requests an address and receives address 192.168.0.1 from > > DHCPServer1. Time passes until half of the lease time has expired so > > Client1 requests an address. This time DHCPServer2 is a little faster > > and provides address 192.168.0.129. > > At 50 percent the client contacts the original leasing server directly to > renew that lease. It does not do a brand new lease broadcast. It will continue > to ask directly until it gets an answer. If it can't it will then broadcast > for a brand new lease. > > > ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ > ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~
