hello all..
i’ve got a question about DHCP Server over L3 links which has been on my nerve for some time now ..
here is the scenario..
my edge router is connected to lan switch using ether2 with ip address of 1.1.1.2/30
i’ve defined required pools and set up dhcp server for each pool
my switch is a L3 cisco switch with 2 Vlans…
Vlan 10 :
ip address : 192.168.10.1/24
Vlan20:
ip address : 192.168.20.1/24
correct configs such as ip helper-address and etc.. has been set
the problem is when the client (on ether vlan) requsets ip address from dhcp server , mikrotik dhcp server always identifies it as conflict and refuses to assign ip address , until i uncheck “Conflict Detection” box on dhcp server config …
i know switch config is correct because it works fine with cisco based DHCP and also Microsoft DHCP , but fails with mikrotik dhcp
i would really appreciate it if you help me on the matter…
thanks
config with screenshots attached mikrotik-config.rsc (1.03 KB) cisco switch config.txt (1.42 KB)
conflict detection sends out a icmp and arp and if it receives a response from either one labels it as a conflict. I would run a packet capture when this happens and find out who is responding,
yes you are absolutely right, after digging a little deeper i found out that the switch interface witch is directly connected to client is actually replying to arp and claming that the IP address is infact present and points to it’s own mac address…really strange … specially since it works OK with Microsoft DHCP …
packet capture snapshot attached
I would still consider this a bug though as it shouldn’t be arping for an ip that is not in a directly connected subnet (IMHO) it should only try icmp.
