DHCP Configuration and Debug on L3 Switch Part

Hello Everyone,

I am writing something after a long time :), today I am just going to cover a very basic configuration of the DHCP on the L3 switch where I will show you how can you verify the debug logs related to the DHCP on the L3 switch and at the same time at the client end. Though it is very basic trust me sometimes it's very important to brush our basics for isolating the bigger problem in the network.

Agenda:

++Configuration at the L3 and L2 switch level, where my L3 switch will act as a DHCP Server.

++ What all packet you will see at the switch level and at the client level.

So below is my topology where you can see one L3 switch which is acting as a DHCP server and I have a directly connected L2 switch where my PC is connected.

L3 switch configuration

I have created SVI for VLAN 70

DHCP_SERVER#show ip interface brief | inc up

Vlan69                 10.106.69.152   YES NVRAM  up                    up

Vlan70                 10.106.70.4     YES NVRAM  up                    up

Fo1/0/2                unassigned      YES unset  up                    up
Fo1/0/7                unassigned      YES unset  up                    up

This is the config for my SVI

DHCP_SERVER#show run interface vlan 70

Building configuration...


Current configuration : 62 bytes
!
interface Vlan70

 ip address 10.106.70.4 255.255.255.0
end

I am creating a pool name 14thDec_REPRO and assigning the network and network mask.

DHCP_SERVER(config)#ip dhcp pool 14thDec-REPRO

DHCP_SERVER(dhcp-config)#network ?

  A.B.C.D  Network number in dotted-decimal notation



DHCP_SERVER(dhcp-config)#network 10.106.70.0 255.255.255.0

DHCP_SERVER(dhcp-config)#DHCP_SERVER(dhcp-config)#default-router 10.106.70.4

 L2 switch configuration

Here also I have created the SVI for vlan 70 but I am not assigning any IP manually to it rather than that I am using the command ip address dhcp so that it can fetch the IP from the DHCP server.

L2_Switch#show ip interface brief | inc up

Vlan69                 unassigned      YES unset  up                    up

Vlan70                 10.106.70.11    YES DHCP   up                    up

GigabitEthernet0/0     10.106.62.68    YES NVRAM  up                    up

TwentyFiveGigE1/0/3    unassigned      YES unset  up                    up

TwentyFiveGigE1/0/5    unassigned      YES unset  up                    up
TwentyFiveGigE1/0/47   unassigned      YES unset  up                    up

Switchport configuration where PC is connected.

L2_Switch#show running-config interface TwentyFiveGigE1/0/3
Building configuration...


Current configuration : 88 bytes
!
interface TwentyFiveGigE1/0/3
 switchport access vlan 70
 switchport mode access
end





L2_Switch#show running-config interface Vlan70
Building configuration...


Current configuration : 41 bytes
!
interface Vlan70
 ip address dhcp
end

For the continuation of this part kindly use the below link where I have continued the rest configuration and debug.

DHCP Debug

DHCP Debug on the L3 switch and I have enabled the DHCP to debug on the switch in order to capture the DHCP packets and events.

Debug from L3 switch side which is acting as DHCP Server

From above you can see that my client a036.9fe7.271f received the IP 10.106.70.13.

Client-Side capture

Here I am not releasing the IP from the client end rather I am sending for the renewal of IP using the command ipconfig /renew on my windows PC. This is the reason my client is sending the DHCP request not the discovery.

L3 Switch side capture which is acting as DHCP server

Client-Side capture in this case

ARP Entry from the switch side