HI,
We have 2 DHCP servers currrently serving per vlan basis - they are microsoft DHCP servers having scope of 80 20 %
Understand that the switch will redirect to either 2 dhcp server randomly for the client Ips. Issue crops up when one of the DHCP server scope is full. The client will not be redirected to the other DHCP server. As a result client will get a 169.x.x.x ips. Can the switch redirect the clients to the DHCP servers based on priority ?
two DHCP per Vlan issue
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cavagnaro
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Re: two DHCP per Vlan issue
Why on earth you have 2 DHCP servers on same network segment?
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eaglecreek
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Re: two DHCP per Vlan issue
the 2 dhcp servers are used as redundancy. for instance IP address scope 10.37.18.0/24 If the the first one goes down, it should go to the next server. However in this scenerio, DHCP server1 does not go down - it merely has IP pool exhaustion. By right DHCP server 1 should redirect the request to DHCP server 2 but in this case it fails.
DHCP server 1 scope would be
10.37.18.5 -10.37.18.200 (80%)
DHCP server 2 scope would be
10.37.18.201 - 10.37.18.250 (20%)
DHCP server 1 scope would be
10.37.18.5 -10.37.18.200 (80%)
DHCP server 2 scope would be
10.37.18.201 - 10.37.18.250 (20%)
Re: two DHCP per Vlan issue
hi,
I'm not sure if you are using ip helper or not but it's not important anyway. If you don't have a ip helper then when client sends a dhcp request it will come as broadcast to both dhcp servers and both of them will reply. Client will choose the first response. If one DHCP server will exhaust its scope it won't simply send any offer and only second dhcp server will send offer. So in normal operation you will use both scopes and no problem. Same scenario will be with ip helper but of course you have to configure 2 ip helpers for each subnet.
Only problem is in case that one server is down - then you have only one scope available. For this case I recommend you to check for DHCP servers which can do load balancing of requests without need of splitting the scope (for example http://dhcpserver.sourceforge.net/)
I'm not sure if you are using ip helper or not but it's not important anyway. If you don't have a ip helper then when client sends a dhcp request it will come as broadcast to both dhcp servers and both of them will reply. Client will choose the first response. If one DHCP server will exhaust its scope it won't simply send any offer and only second dhcp server will send offer. So in normal operation you will use both scopes and no problem. Same scenario will be with ip helper but of course you have to configure 2 ip helpers for each subnet.
Only problem is in case that one server is down - then you have only one scope available. For this case I recommend you to check for DHCP servers which can do load balancing of requests without need of splitting the scope (for example http://dhcpserver.sourceforge.net/)
