would I need DHCP helper cmds under a Switch Uplink to the firewall? Firewall is doing the routing.

[m-abooali]

Hello,

we are using a stack of Cisco 3750 TS all sfp switches to act as core switch and few stack of two Cisco 3750Gs. the SonicWall firewalls are doing the actual routing except for 0/0 [firewall IP address] in switches. my question is if I need to add the dhcp helper cmds under my uplink connection to the firewall. I believe that Sonicwallls or one of them is set as DHCP server. I do not manage that.

Best Regards,

Masood

[Francesco Molino]

Hi

I'm sorry but I didn't understand quite well your design and question.
If your 3750TS stack switches are acting as core switch, this means all your SVI (L3 interfaces for all your vlans are hosted on him). IP helper command will be configured on his SVIs to direct dhcp requests to your DHCP server. Do you already have ip helper commands setup? If so, you can determine the IP address of your DHCP and validate if your DHCP is your sonicwall or a dedicated server.

As soon as your DHCP is not your core switch you will need ip helper command on every SVI (vlans) except the one where the DHCP is sitting on.

[m-abooali]

Hi and thanks for you answer, you are correct, all my SVIs for vlans are hosted on this stack. Since DHCP was running on SonicWall and out of my control, I did not ass any dhcp helper CMDs on this so called Core Switch stack that is as said hosting all SVIs.

So, I need to put dhcp helper cmds under each SVI interface?

If so, please advise. All traffic is already routes to the one Sonicwall that is also dhcp server, so please advise if I need commands under each SVI interfaces and what commands pleases.

Dhcp been working so far but I was suspecting some kind of a slowness.

Ppl are connecting to this location through VPN also configured on the SonicWall.

I am sorry if I wasn’t clear enough.

Best Regards,

Masood

[Francesco Molino]

What is the actual configuration of each svi? Do they have ip helper command configured against your firewall?
You said they are working, but what is your actual dhcp server?

[m-abooali]

Hi,

Yes without helper command things was working but taking a little time to acquire IP so I added up helper cmd under each SVI interfaces since diff vlan have diff DHCP server on diff firewall. Three firewalls running dhcp server for diff vlans.

After adding the IP helper cmd thing improved but IP helper cmd was all I added under each SVI interfaces on the switch that was hosting those SVIs.

Best Regards and thanks for responding.

Best Regards,

Masood

[Francesco Molino]

Good that works fine now.

[Reza Sharifi]

Hi,

my question is if I need to add the dhcp helper cmds under my uplink connection to the firewall

No, if the core switch stack is layer-2 only and the firewall is doing all the routing then the helper address should be configured on the firewall. 

HTH

[m-abooali]

Thanks. That is what I was thing but this so called core stack is hosting all my SVI Interfaces. It has 0/0 to firewall IP address.

All other Cisco 3750Ga also pointing to this core and from core to Firewall.

I.e. 0/0 to Core IP

>From Core 0/0 to firewall IP.

Best Regards,

Masood

[Reza Sharifi]

Ok, so the core is not just layer-2. It is layer-2/layer-3 since it hosts all the SVIs. In this case, the helper address needs to be added to all user-facing SVIs to provide IP to end devices.

HTH

[Jaderson Pessoa]

You need aplly it on svi if there are.. or directly on interface on your switch-core to dhcp server (in your case,firewall)