Tuesday, August 30, 2016

Setting up DHCP address reservation

Good afternoon everyone, in this brief post I will talk about how you can enable DHCP address reservation on your router. For demonstration purpose I'm using a TP-Link router which is very common but any other brand of router should have the similar option too.

Before getting into how to do it let's discuss DHCP. It stands for Dynamic Host Configuration Protocol and as it's name suggests it is an network protocol used on Internet network protocol. This protocol is controlled by a DHCP server to dynamically distributes network parameters such as IP addresses. So it drastically reduce the workload for the network engineer who is in charge with deploying a network. If DHCP wasn't available network engineer or the person who is setting up the network has to manually assign IP addresses to all the devices but with DHCP the server itself assigns IP addresses to devices automatically. Connect a new device and it will get a new IP automatically, you don't have to do anything. If you think about depleting IP addresses then lease time will help you with that. Unused IP addresses will be re-cycled via this. DHCP server leases IP for certain set period of time, if after that time the device no longer needs the IP it will be assigned to some other device. So it's all well and good right then where is the point of reserving certain IP?

Here is the thing, if you are running a network attached storage or IP TV or media center then DHCP might not be ideal as it will change the IP address over time. Say if you configure your phone to get certain data from certain IP, if that IP changes it will no longer get that data, you will have to enter the new IP. Now if you completely turn off DHCP then again you have to manually set all the IP addresses for different devices. Hence DHCP address reservation. In this method what is done is simply reserve certain IP address to certain MAC address or device address so that that IP won't be given to anyone. This ensures that certain devices will always get certain IP addresses. For example I always reserve IP address for my Raspberry Pi so that I can easily SSH into them. Let's look at the procedure then.


Procedure:

1. Get into the router via the web based interface, for different router it might be different for example
Tp-link can be accessed with http://192.168.0.1/ or tplinklogin.net
SMC can be accessed with http://192.168.1.1/



After that login with the username and password, it should be written under the router or on the box if you haven't changed it yet.

2. After getting into the router you will be greeted with this page where you should find something like DHCP. We need to get into that too


3. Now getting into DHCP we will find the options for turning it on or off. Default it should be enabled and we want to keep it that way.


4. Next we need to go to the DHCP Client list to get the MAC address for our client. If you can't determine the device from the client name, for example it is very tough to determine android devices so in that case you might want to gather the IP address or MAC address from the device itself. Keep that MAC address in mind to assign the IP address that you want to assign. Remember the lease time I was talking about? Look carefully and you will see some devices have their IP address with lease time, after the expiration either those IP addresses will be renewed or given to some other device if needed. Those with the Permanent lease time are reserved.


5. Now let's move on to the final part the Address reservation, in here you will see any existing one that is already configured or you can add/modify/delete any entry.


6. As I already have couple devices configured to have same IP address all the time those devices are already listed here. If you are doing it for the first time you will see an empty table. To add a new entry you simply click Add new and put in the MAC address and IP address and done. You might want to restart the router afterwards.


So that's how easy it is got enable DHCP address reservation and saves a lot of time finding IP addresses of devices. Now for an example I will always reach my Raspberry Pi 2 at 192.168.0.103

Hope it has helped.

Read my other posts here.

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