DHCP config

[Andrew White]

Hello,

I'm trying to come up with a solution to add DHCP to a LAN config similar to the diagram below:

Info

• Both cores are connected via an etherchannel.
• VLANs 30,40,50,60,70.
• Both cores are in HSRP groups for each VLAN (for example "standby 30 has an IP of 192.168.30.254 and core 1 is 192.168.30.252 and core 2 192.168.30.253).
• Standard trunks to each core from the L2 switches, with one port blocking due to spanning tree.

I need to provide redundancy via a router or L3 switch to all the vlans and provide redundancy.  What is the best way to do this?  IPhelper, SVIs on the DHCP server for each vlan etc.  I have the scopes created on the DHCP server, but am not sure of the links from the DHCP server should be L3 ports like a router on a stick, trunk ports etc.

Thanks

[Karsten Iwen]

Is there only one DHCP-server? Then there is at least one singe-point-of failure.

For the rest I would follow a "keep it simple" approach. No SVIs or trunks to the DHCP-server but just one VLAN with one IP on the DHCP that gets the DHCP-packets through IP-helper. With only one VLAN you have spanning-tree to the cores and onle link gets blocked. Easy and simple.

[Tagir Temirgaliyev]

you can configure 2 dhcp servers on core1 and core2 with the same scope and they will work. and you will have dhcp redunduncy

and dont forget to rate post

[Andrew White]

Well originally I did keep it simple using the IP helper address in each vlan on each core. I put the dhcp server on a different subnet, 192.168.41.0/30 and 192.168.41.4/30 for the other interface and on the cores I made them a L3 interface. However when a client on the 90 vlan for example requested an IP address it when get to the dhcp server, but the debug dhcp message would say there was no scope for the 192.168.41.x subnets which was strange. The dhcp server doesnt know it was requested from the 90 vlan subnet.

[Karsten Iwen]

That strategy is what I would see as an easy solution. If something didn't work there, I would better first investigate why the DHCP-messages were sent to the server incorrectly.