DHCP relay and server in Computer Network

To assign an IP address to the host dynamically, DHCP client exchange DHCP messages with DHCP server in DORA process.

Whenever a computer or different networked device connects to a network, the DHCP patron software program sends a broadcast question soliciting for important statistics. Any DHCP server at the network may additionally service the request.


With this DORA process, the discover and request message is broadcast, the offer and the acknowledgement message is broadcast or unicast depending upon the value of broadcast flag i.e. If the value of broadcast flag is 1,then the offer and acknowledgement message is broadcast and if 0,the messages are unicast. But this is valid only when the DHCP server is present in the same network because the router doesn’t forward any broadcast packet. What if the server is present in a different network? Here comes the role of DHCP relay.


The DHCP server manages a pool of IP addresses and records approximately patron configuration parameters together with default gateway, area call, the call servers, and time servers. On receiving a request, the server might also respond with unique facts for each patron, as previously configured by means of an administrator, or with a specific address and any other facts legitimate for the entire network and for the time period for which the allocation (lease) is valid.


A consumer generally queries for this facts immediately after booting, and periodically thereafter before the expiration of the facts. when a DHCP client refreshes an challenge, it first of all requests the same parameter values, but the DHCP server can also assign a new cope with primarily based on the venture rules set by means of administrators.



DHCP server


Citrix SD-WAN appliances can be configured as DHCP server. It can assigns and manages IP addresses from specified address pools within the network to DHCP clients. The DHCP server can be configured to assign more parameters such as the IP address of the Domain Name System (DNS) server and the default router. DHCP server accepts address assignment requests and renewals. The DHCP server also accepts broadcasts from locally attached LAN segments or from DHCP requests forwarded by other DHCP relay agents within the network.


The DHCP protocol become created in order that clients may want to reap their IP cope with automatically and with out human intervention (yes that used to be an real a part of IT-ing, back within the day). The manner this works is that once a consumer connects to the network, it sends out a “broadcast” packet asking to find the DHCP server.

DHCP SERVER

That was “good enough” till Vlans got here along. Vlans create obstacles and segment your physical community into several really isolated ones (therefore the name V-LAN). one of the downsides to Vlans is that now the DHCP server and the clients can’t at once talk, due to the fact “broadcast” packets can not “bounce” networks. So, how do you avoid having a DHCP server per-Vlan, and supply the DHCP requests from the customers in a Vlan, lower back to the vital server?


DHCP relays had been invented to over come this actual hassle through basically “routing” or “proxy-ing” the consumer’s requests. The requests are broadcasted through the customers on their neighborhood network, the relay-agent catches them and forwards them to the DHCP server the use of uni cast. The back DHCP answer gets to the relay agent using uni cast as properly, and the relay agent sends the answer on the consumer’s network.


DHCP provides a framework for passing configuration information dynamically to hosts on a TCP/IP network. A DHCP client is an Internet host using DHCP to obtain configuration parameters such as an IP address.


DHCP relay

A DHCP relay agent is a host or router that forwards DHCP packets between clients and servers. Network administrators can use the DHCP Relay service of the SD-WAN appliances to relay requests and replies between local DHCP Clients and a remote DHCP Server. It allows local hosts to acquire dynamic IP addresses from the remote DHCP Server. Relay agent receives DHCP messages and generates a new DHCP message to send out on another interface.

DHCP Relay

Below are the benefits of using the DHCP server and DHCP relay features:

• Reduce the amount of equipment at client site.
  
• Replace router at client site (Easy deployment of edge router services).
  
• Simplify the client site network.
  
• Configuration of Router without CLI commands.
  
• Reduce manual configuration on simple client sites.

You can configure the DHCP relay agent at both the context and VLAN interface levels of the ACE.


If you configure the DHCP relay agent at the context level, the configuration applies to all interfaces associated with the context.
If you configure the DHCP relay agent at the VLAN interface level, the configuration applies to that particular interface only; the remaining interfaces revert to the context level configuration.


Configurations :

This is the basic configuration of the client, router, dhcp_server.The router has been assign IP address 192.168.1.1 on fa0/0 and 192.168.2.1 on fa0/1.

The DHCP_SERVER is assigned IP Address 192.168.2.2 on the interface fa0/0 and the DHCP pool is defined with name POOL1 and network of 192.168.1.0 with subnet mask 255.255.255.0 is assigned to the pool POOL1.

Now, the ip helper address command is used for configuring the router as a dhcp relay agent, giving 192.168.2.2 the address of DHCP_server.