IP Helper-address command - Page 4

MATT ALLEN · ‎10-23-2015

before i ask my question let me give a little bit of background information. I am setting up multiple vlans on my network, vlan 301-304 and they are all going over a single switch port to another device.

vlan 301 has a SVI IP of 192.168.1.1,

vlan 302 has a SVI IP of 192.168.2.1,

vlan 303 has a SVI IP of 192.168.3.1,

vlan 304 has a SVI IP of 192.168.4.1

all have a mask of 255.255.255.192 and all have the ip helper-address ip of 192.168.2.150.

the IP of the router layer 3 port is 192.168.2.253 255.255.255.248

the IP of the router is 192.168.2.254 and all the routes back to the SVI are in the router

the ip of the dhcp server is 192.168.2.150 and it resides in vlan 1 that has an ip of 192.168.2.140 255.255.255.224

I have no problems routing traffic to and from the router. my problem is the pc on and of the vlans can not get dhcp from the dhcp server. on the dhcp server i can see the requests for an ip and where it is offering the ip but the pc never receives it. I am using a catalyst 3850 switch and a cisco 3700 series router.

Richard Burts · ‎10-30-2015

It seems to me that there is some confusion and shifting back and forth whether we are talking about gateway in the scope of various subnets or talking about the gateway for the DHCP server. The gateway of the DHCP server should be the IP address of the router/switch interface in the subnet to which the DHCP server connects. In the original post we were told this

the ip of the dhcp server is 192.168.2.150 and it resides in vlan 1 that has an ip of 192.168.2.140 255.255.255.224

If that is correct then it seems that the gateway for the DHCP server should be 192.168.2.140.

HTH

Rick

HTH

Rick

Masoud Pourshabanian · ‎10-30-2015

Gateway must be within the range of your ip address and also in the same broadcast domain. Because Your DHCP finds its gateway by ARP and ARP does not pass L3 interfaces.

In your case, The gateway of your DHCP server must be the interface on your router which is toward your server. Both need to have the same subnet to avoid any strange behaviour.

Try to correct the subnet and check Debug DHCP again. I am mostly suspicious to the DHCP server configuration and then Trident.

Masoud

Masoud Pourshabanian · ‎10-29-2015

As John mentioned, your switch does get any response back from DHCP server.

Does your DHCP server ping 192.168.3.1?

Any firewal is activated on DHCP server or router?

Try to bypass Trident by connecting your DHCP server directly to the router on a L3 interface when your network is not being used.

After trying those, If you still have problem, just focus on the configuration of your DHCP server.

jeffrey_craig1 · ‎10-30-2015

Dont know what \/ on about ! your ip address od dhcp server and ip helper address are the same! however mate sounds like you have everything in order. check trunks mate common error. :)