> I thought that receiving multiple DHCPOFFERs could cause > problems on the client, but I see in RFC2131:
Well, we ran a university on two dhcpds which both held all static entries, and then they had 50% of the dynamic each so most of the clients were using fixed mac -> ip mappings and we never saw any issue with them hearing two answers, especially not with the same ip. I can't promise they only used first answer, but it stands to reason that most tcp stacks in some sense act like this: 1.send broadcast for an ip 2.receive one reply packet to your mac with an offer for an ip 3.reply with unicast to the server that you accepted the offer, stop listening, act on this packet like setting interface ips and so on 4. move on The less advanced the client is (IoT light bulb?) the more likely it would be to act as above, and not go on trying to collect another answer or something. If an udp comes at your box after step 3, you just drop it because you are no longer listening for whatever comes your way on udp port 68. > So my conclusions are that: > 1: multiple DHCP offers from multiple dhcpd's are not a problem > 2: synchronization of N dhcp servers (with -y and -Y ) is useful to keep the > same address > for the same client even if the previous (stored on the client) dhcp > server goes down > 3: carp is not needed If you have them on the same network, it might be an idea to carp them so they do not needlessly both respond to dynamic requests and race each other, but this brings some other complexities. At other places we just had rather long TTLs on the leases and if the main box crashes, another starts dhcpd and serves new requests as best it can. For fixed stuff, nothing really changes and dynamic clients should handle dynamic ip changes in the worst case. With hours for ttl, you often can get the service back up in the window between renewed-lease-time and end-lease-time given that dhcpd is a rather simple service even if you have to reinstall a box, pkg_add dhcpd and grab configs from backup/versioning again. -- May the most significant bit of your life be positive.
