DHCP with Router on a Stick fails; instead uses APIPA.

[schaeard000]

Hello, I was working on a topology that incorporates inter-vlan routing as well as dhcp pools for each vlan. I got my inter-vlan routing to work with static addresses, and all devices can ping the default gateway currently. The router acting as the dhcp server can ping the router that has all the sub-interfaces for the router on a stick. I have configured all sub-interfaces to have a helper address of the said dhcp server. However, PC1, the device I am using to test dhcp is not receiving the address correctly.

I have included my pka below. Thanks in advance.

[mwaltner12]

Everything is correct, except your dhcp server has no route to give clients their ip. Just add a default route and it works.

[Georg Pauwen · Accepted solution]

Hello,

the subinterface 0.99 on the router needs to have the 'native' keyword as well. You also need routing between the routers (static default routes at least). And last but not least, your access ports need the 'spanning-tree portfast' command.

Find attached the revised, working file.

[Gopinath_Pigili]

Hello schaeard000 ,

Make the following changes...it will work...

R1

interface FastEthernet0/0.99

encapsulation dot1Q 99 native

ip address 192.168.99.1 255.255.255.0

ip helper-address 216.100.100.1

R1(config)#ip route 0.0.0.0 0.0.0.0 fa0/1

DHCPSERVER(config)#ip route 0.0.0.0 0.0.0.0 fa0/1

Best regards

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[schaeard000]

Thank you for your answer. I had not learned about static routing yet so this helped me figure it out.