CCNA 200 - 301 - Lesson 90: Understanding and Configuring DHCP Relay
Section - 20: Mastering IP Services
Lesson 90: Understanding and Configuring DHCP Relay
We are back again with a new video in our Free CCNA Course series. In this video, we will discuss the concept of DHCP Relay. Let’s start -
What is DHCP Relay?
DHCP relay means that your DHCP server is not a member of the same broadcast domain. There are also certain DHCP relay agents who are used to forward DHCP relay packets between the clients as servers. In other words, they forward messages and replies between the clients and servers.
How to configure a DHCP relay?
You can see that for LAN 1 or LAN A, if R2 is configured as the DHCP server in that case R2 is not a member of the same broadcast domain.
So by default, to get the IP address the first message sent by the client will be the DHCP discover packet which is always broadcast in nature. It can’t cross a Layer 3 boundary, which indicates that if a client is generating a broadcast packet it will be received by the first hop router and that router can’t forward the concept any further. What needs to be done in such a case is, we can use the DHCP relay.
Here, whenever the First Hop Router is R1 on interface fa0/0 receives any DSP Discover packet, it will be told to send it to the exact server. Once the command ‘IP Helper Address’ is run your DHCP relay will end configured. The DSP packet will be sent to the server 12.1.1.2.
This is the basic use of the DHCP relay when you don’t have the DHCP server in your own LAN or domain. You can check the bindings on R2 by using the command ‘show IP DHCP binding’. It will reflect that the same DHCP server is providing IPs to the 20s LAN and 10s LAN both, so you can see the IPs of the users from both the networks.
Hope, you were able to follow the configuration steps and if you lost anywhere in the middle, then just write to us in the comment section!
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