2

The screenshots of the network topology below,

Router 0 is a DHCP server and Router 1 I assume should be a relay agent. The routing protocol I use is EIGRP.

The problem is that PC in vlan 15 and vlan 20 cannot get the ip addresses from the dhcp server. I found out that we can configure ip-helper on the switch but it didn't work either. sh ip route command shows that it can see all networks. You can't see dhcp pools for vlans 15 and 20 on the screenshots but I configured them.

I think I miss some information about vlans or something. Can somebody point me where the problem is?topology

second

2

Configuring a DHCP relay on Cisco routers is pretty simple. You use the ip helper-address <DHCP server address> command on the layer-3 interface. The address for the helper address must be reachable from the router on which the helper address is configured, e.g. the Router0 interface toward Router1.

You are putting the helper address on the physical interface for which there are no VLANs. You need to put the helper address on the individual subinterfaces (each subinterface could use a different DHCP server).

Your DHCP server must have a scope for each of the networks for which it is the DHCP server.

By the way, never use a picture for text in your question. Just copy the text and paste it into your question, highlight the text, and use the Pre-formatted Text button: {}.

Edit:

Your Router0 needs scopes for VLANs 15 and 20:

ip dhcp pool vlan15
 network 195.165.85.96 255.255.255.224
 default-router 195.165.85.124

ip dhcp pool vlan20
 network 195.165.85.128 255.255.255.224
 default-router 195.165.85.158

Router1 needs helper addresses on the interfaces:

interface GigabitEthernet0/1.15
 encapsulation dot1Q 15
 ip address 195.165.85.124 255.255.255.224
 ip helper-address 195.165.85.29

interface GigabitEthernet0/1.20
 encapsulation dot1Q 15
 ip address 195.165.85.158 255.255.255.224
 ip helper-address 195.165.85.29

You also need to make sure that Router0 can ping the G0/1.15 and G0/1.20 interfaces in Router1.

  • You mean to configure ip helper-address going on the int vlan 15 and vlan 20 and point them to the main dhcp server which is router 0? So I did that, it still does not work. Do I have to configure routing on the subinterfaces as well? – Josh Sep 19 '16 at 1:57
  • What is the Router0 interface address for the interface with the link to Router1? – Ron Maupin Sep 19 '16 at 1:59
  • Router0 g/0 ip address is 195.165.85.29 and Router1 g/0 ip address is 195.165.85.30 – Josh Sep 19 '16 at 2:02
  • See the edit to my answer. Also, You really need to edit your question to put the text into the question, instead of having the text in a picture. Keep the network diagram as a picture, but copy and paste the text into your question. – Ron Maupin Sep 19 '16 at 2:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.