Options handling for Unicast packets in RENEW State

venkataramana.kaza at wipro.com venkataramana.kaza at wipro.com
Mon Mar 26 07:09:37 UTC 2007


Regarding giaddr not being set, the requirement of the DHCP option82 feature in Relay Agent operating at Layer 2 was not to set the giaddr field in the DHCP packets.

We are not sure why ISC DHCP server need to take decision of echoing DHCP option82 tag based on giaddr field. Our Relay Agent does not set giaddr field even in INIT state, but proper replies are received in that case. 

It looks like, DHCP server does not echo option82 tag only in the case when unicast packets are sent to the client.

Secondly, according to the standards, RFC 3046 and TR-101, it is not mandatory to add DHCP option82 tag by relay agent in DHCP client RENEW state. The operations of DHCP relay and DHCP server is such cases is based on implementation. In our Relay Agent, since the DHCP option82 feature is only for adding/removing DHCP option82 field, it always expects option82 tag to be present in all DHCP downstream packets. To substantiate the same, TR-101 also states that DHCP server must always echo back the option82 tag. "The DHCP server must echo this option unchanged from request to response, but may examine its contents." (Ref:TR-101, Appendix B, Page 93) 




>-----Original Message-----

>From: dhcp-users-bounce at isc.org 

>[mailto:dhcp-users-bounce at isc.org <mailto:dhcp-users-bounce at isc.org> ] On Behalf Of ext David W. Hankins

>Sent: 23 March, 2007 20:44

>To: dhcp-users at isc.org

>Subject: Re: Options handling for Unicast packets in RENWE State


>On Fri, Mar 23, 2007 at 05:56:08AM +0530, 

>venkataramana.kaza at wipro.com wrote:

>> When the DHCP Server is receiving the Unicast Packets (in RENEW 

>> State) with Option 82 added, it is stripping it off and


>> Sending the responses with out the Option 82 attached.


>It's been recently (today) brought to my attention that the 

>server does not reply with the relay agent information option 

>specifically in the case where the relay agent does not set giaddr.


>> As per our understanding the Relay Agent can expect the 

>Option 82 from the Server Responses due to Security reasons.


>Security reasons? I'd never heard that before.


>The relay agent options are usually echoed back as a hint to 

>the relay on how to locate the client.



>ISC Training! http://www.isc.org/training/ <http://www.isc.org/training/>  training at isc.org 

>Washington DC area, April 16-20 2007. DNS & BIND, DDNS & DHCP.


>David W. Hankins "If you don't do it right the first time,

>Software Engineer you'll just have to do it again."

>Internet Systems Consortium, Inc. -- Jack T. Hankins



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