Dhcp not working

[mgutierr]

I have 3 vlans on a C9300 4 switches stack

have vlan 112 -> 172.16.112.0 (data)

       vlan 312 -> 192.168.112.0 (voice)

       vlan 221 -> 10.1.112.0 (wireless)

and a dedicated windows server for dhcp scopes for each single vlan. (172.16.0.109)

ping from the C9300 to the dhcp works fine

VLAN 112 is gathering dhcp but VLAN 221 is not , so any device connected from gi 4/0/31 to 4/0/48 is not getting

10.1.112.X address from the scope, if i do setup manually static ips on any device it works.

i'm pretty sure that you guys are going to be able to help me out

[mgutierr]

from the other end i got

show ip route 10.1.112.1
Routing entry for 10.1.112.0/22
Known via "eigrp 10", distance 90, metric 3072, type internal
Redistributing via eigrp 10
Last update from 172.16.254.112 on Vlan254, 22:40:01 ago
Routing Descriptor Blocks:
* 172.16.254.112, from 172.16.254.112, 22:40:01 ago, via Vlan254
Route metric is 3072, traffic share count is 1
Total delay is 20 microseconds, minimum bandwidth is 1000000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 51/255, Hops 1

[mgutierr · Accepted solution]

Let me answer myself on this matter:

the answer is pretty much related to DHCP protocol and how cisco handles it,

1st.

since DHCP sends broadcast traffic to a vlan it has to be controlled, so by default you just have to assign 

an ip helper-address to manage dhcp requests out of your vlan.

2nd.

check if your switch has dhcp relay service enable, for my particular model (C9300) i did delete and option that was preventing dhcp to run : no service dhcp

hope it help somebody with the same issue

[Agustin9991]

Hi all,

I had the same problem and the solution was to add the following commands in the vlan interface configuration:

ip dhcp relay information trusted
ip dhcp relay information option-insert
ip dhcp relay information check-reply

i.e.:

interface Vlan1012
description Telefonia Placa 1
ip dhcp relay information trusted
ip dhcp relay information option-insert  
ip dhcp relay information check-reply  
ip address 10.171.0.1 255.255.252.0
ip helper-address 10.103.0.1  
load-interval 30

Then the relay started working. Removing the previous config it kept running

Best,