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hardware type in dhcp messages

Hi,

please help me to understand that why should determine hardware type (htype) in dhcp messages on second field?

I think the server knows that in which type network sends its messages

why is it important?

I attach the dhcp message below.

I apologize for my bad English:>

 

1 ACCEPTED SOLUTION

Accepted Solutions

You are welcome. That field is defined in DHCP to make it compatible with BOOTP protocol which used the field. It matters to the server because the type of hardware address (and the length of that address) vary depending on the type of network (think, for example, about the hardware address of Ethernet (mac address), or HDLC, or Frame Relay (DLCI) which are quite different).

DHCP does not necessarily provide different messages per hardware type. But it does use hardware type as part of its processing to identify the client who sent the request.

This question is perhaps more complex than you realize "can we define different pool according to hardware type?" If a DHCP server receives a request from a client with a hardware type of Ethernet and receives a request from a client with a hardware type of Frame Relay it will certainly need a unique pool for each. But the requirement for separate pools is not based on hardware type but is based on the fact that the Ethernet client and the Frame Relay client are obviously in different IP subnets, and each IP subnet requires its own unique pool. 

 

HTH

Rick

View solution in original post

6 REPLIES 6
Richard Burts
Hall of Fame Guru

There are many participants in the community for whom English is not their primary language and we try to accommodate this. I believe that we will be able to communicate adequately. 

First let me say that it is not true that the server would know which type of network the client is in. If the server and the client are in the same network then certainly the server knows the type of network. But if the server is in one network and the client is in a different network (as is frequently the case) then the server has no knowledge of the network type of the client. Let me also say that while in the networks in current times where the client is connected are mostly Ethernet, that in the time when the standard for DDHCP was developed there were many other network types that were being used.

As to why htype is important we should recognize that the hardware address (like the mac address for Ethernet) is dependent on the media where the client is connected. It would make a difference if the client were connected via HDLC, or by Frame Relay, or by Fibre Channel, etc. The htype field is provided so that the server can understand the environment of the client.

Perhaps this article will supply helpful information

http://www.tcpipguide.com/free/t_DHCPMessageFormat.htm 

HTH

Rick

Thank you for your attention.

why server needs to this information?

Does it provide different message for different network (wireless or fiber channel)?

or can we define different pool according to hardware type?

 

 

You are welcome. That field is defined in DHCP to make it compatible with BOOTP protocol which used the field. It matters to the server because the type of hardware address (and the length of that address) vary depending on the type of network (think, for example, about the hardware address of Ethernet (mac address), or HDLC, or Frame Relay (DLCI) which are quite different).

DHCP does not necessarily provide different messages per hardware type. But it does use hardware type as part of its processing to identify the client who sent the request.

This question is perhaps more complex than you realize "can we define different pool according to hardware type?" If a DHCP server receives a request from a client with a hardware type of Ethernet and receives a request from a client with a hardware type of Frame Relay it will certainly need a unique pool for each. But the requirement for separate pools is not based on hardware type but is based on the fact that the Ethernet client and the Frame Relay client are obviously in different IP subnets, and each IP subnet requires its own unique pool. 

 

HTH

Rick

View solution in original post

Thanks for your reply.

You are welcome. I am glad that my explanation was helpful.  Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick
MHM Cisco World
Collaborator

hardware type use in network that have wire and wireless, this make DHCP give IP different for each one.