In this article, we study how to activate the DHCP relay on the router to forward requests from clients located on a different network.
To better understand the problem, we will quickly review the functioning of DHCP protocol.
In this article, we will learn how to set up a HTTP tunnel between a PC and a Linux server with the SSH protocol to secure our transactions through a firewall or another.
Before to begin any technical part, I will try to explain the operation of Port Forwarding and why implement it.
To understand this concept, I refresh your memories on the communication of computer:
To exchange informations, computers need an IP address and a port number. The port number is important because it’s thanks to it that the communication exists. Client and server have to communicate on the same port number.
Now, we decrypt the Port Forwarding. The Port Forwarding consist of redirect informations sent on a port number of a computer to a different port number on another computer.
For this first article, we will see how to set up a DHCP service on Cisco routers.
DHCP Service (Dynamic Host Configuration Protocol) allows users to obtain IP configuration automatically.
The DHCP service is often coupled with DNS service on a dedicated server. However, it is possible to activate it on a router for a small network.
An configuration has an IP address, its subnet mask and others options. Forty of them are configurable such as the default gateway, DNS servers, domain name and WINS server.
A client has a configuration during a specified time, we call it: the lease.
Note : DHCP uses broadcast to communicate, which means that the client’s request can’t cross a router (except explicit command).
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