DHCP Relay Issue

[OddievenInc]

Hi everyone, 

I'm having issues with obtaining DHCP from a different subnet. Did some troubleshooting, but got to the point where I had to reach out for support. 

I'm trying to obtain a DHCP IP for the client directly connected to the Branch Office Core switch. I can ping the DHCP Server IP from the branch office core switch. 

Attached is the topology, and configuration related to the DHCP relay etc. Is this viable? If it's wrong what is the correct way of setting things up? Appreciate your time and comments.

[marce1000]

 - Diagram is a bit overwhelming , on a first reply ; did you define a dhcp relay statement in the vlan configuration for clients to be able to find a dhcp server when using that particular vlan ?

 M.

[OddievenInc]

HI thanks for the response. As you can see, have configured ip helper-address under the interface vlan 10 on the branch office core switch. The client connecting to the switchport is, on access vlan 10

[marce1000]

    - Not  sure how far troubleshooting was done so far ; concerning the DHCP server , 
      on IOS you have   debug dhcp detail                for instance and
                                 debug  ip dhcp server events
     Look for similar commands on your dhcp server platform (if applicable)

      + I notice that this is a branch office , make sure no  corporate dmz-firewalling blocks full dhcp services
         towards the branch office , 

                You may also find this useful : https://networklessons.com/cisco/ccie-routing-switching-written/troubleshooting-dhcp

 M.

[OddievenInc]

Hi 

Thanks again for the reply. Appreciate it. I have done debugs & taken monitor session captures. Also, there is no firewall in the middle. ISP has allowed all communication. ISP link is L2, but local termination is L3 (as you can see in the topology) Do you think this should work? Or is there something that i have to look at in terms of the design?

[marce1000]

                            >..., but local termination is L3 
    - This might be an issue because ISP's normally expect ip traffic and dhcp is layer2 , you may need to contact the ISP
      and check if what you want can be done, In the mean time you could deploy a dhcp server on the branch office 
      (temporarily) .

 M.

[Martin L]

PC connected to switchport in vlan 10 ? there is no DHCP for network 10, I think I see one DHCP pool for vlan 30 or 36; 

Try connecting PC to switchport on vlan 30 or 36;  Or add another pool for vlan 10 network

Then, every L3 port (switchport and interface SVI port) needs ip helper address x.x.x.x 

Regards, ML
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[OddievenInc]

Hi thank you for the reply. Noted. The things here, is that I have clients in the Head Office configured under vlan30 to receive DHCP IPs, (locally) from the DHCP pool vlan30. I want to extend that same DHCP pool for the Branch Office users in vlan10. Is this even feasible? Because I can only have the SVI for vlan30 (DHCP Pool vlan30) configured in the Head Office core switch. 

[marce1000]

                - I believe you can always create another SVI too

 M.

[OddievenInc]

Made some changes. Pls refer below. 

I have configured 'interface vlan 10' in both branch office and head office. Pls refer below. Will the branch office send the DISCOVER Packet out of it's exit interface? and reach the Head Office core switch where the DHCP Pool is located, and ultimately client connected to the branch office in vlan 10 access port getting an IP address. 

[MHM Cisco World]

two same VLAN in two two sites and using ip helper using same subnet, 

that not work 
you have ISP-ISP L2 but the site stack SW to ISP is L3 ??? can you more elaborate

MHM 

[Martin L]

"extend vlan 30 DHCP pool for the Branch Office users in vlan10." - I do not think that is possible. I am not aware of any trick that would make this; Every vlan has its own pool with its own subnet; Vlan 10 is under subnet 10.140.48.0 interface vlan 10;  you should have separate pool for vlan 10.  

Regards, ML
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[OddievenInc]

Hi

Thank you for the reply. Appreciate it. 

I have made some changes. Pls refer below. Would this suffice? 

[MHM Cisco World]

you topolgy is nice but some point not clear 
where is dhcp server?

where client connect to?

MHM

[Harold Ritter]

Hi @OddievenInc ,

The host in the branch should get an address from the subnet it is connected to (10.140.48.0/22). Trying to get an address from a pool from another subnet will not work.

You should define a pool locally on the branch office switch.

ip dhcp pool vlan10

network 10.140.48.0 255.255.252.0

default-router 10.140.48.1

dns-server 8.8.8.8

!

interface vlan10

no ip helper-address 10.140.36.1

Regards,