Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

Bronze

Remote id suboption in dhcp option 82

I have a quick question on DHCP option 82. In Remote ID suboption, there is a Cisco proprietary 2 byte RID type and length that is added.Is there any other dhcp server other than cisco ios devices,which can be used to insert this Remote ID suboption.

The remote-id type and length of remote-id type is not defined as part of any RFC and looks like is Cisco proprietary.

Please refer to the Option-82 Data Insertion here

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_58_se/configuration/guide/swdhcp82.html#wp1069615

  • LAN Switching and Routing
2 REPLIES
Cisco Employee

Re: Remote id suboption in dhcp option 82

Hello Ankur,

Sorry for the late reply. Let me take it from a bigger perspective.

RFC 3046 defines the Option-82 as a container that can hold a set of suboptions. The same RFC establishes two initial suboptions:

  • Type 1: Circuit ID
  • Type 2: Remote ID

Suboption numbers are currently numbered by IANA and this is the current type allocation list:

http://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xml#relay-agent-sub-options

The server behavior over diverse Option-82 suboptions is defined with respect to individual suboptions, i.e. the processing of different suboptions by a DHCP server may differ. Now, both Circuit ID and Remote ID suboptions are defined as opaque values that should not be internally interpreted by the server:

Section 3.1, Agent Circuit ID Sub-option

   Servers MAY use the Circuit ID for IP and other parameter assignment
   policies.  The Circuit ID SHOULD be considered an opaque value, with
   policies based on exact string match only; that is, the Circuit ID
   SHOULD NOT be internally parsed by the server.

Section 3.2, Agent Remote ID Sub-option

   DHCP servers MAY use this option to select parameters specific to
   particular users, hosts, or subscriber modems.  The option SHOULD be
   considered an opaque value, with policies based on exact string match
   only; that is, the option SHOULD NOT be internally parsed by the
   server.

Furthermore, the entire Option-82 is intended to be processed by the very device that originated it. Other devices are not supposed to act upon a Option-82 value they have not originated themselves (although there is no 100% guarantee provisioned to make sure that a device won't confuse a different Option-82 for its own).

From all of this it follows that both Circuit ID and Remote ID may contain arbitrary values and they are totally vendor-dependent. So, yes, the format of Circuit ID and Remote ID as used by Cisco for DHCP Snooping purposes is proprietary - it uses the correct suboption header of the suboption type and length and follows with proprietary data - but that is expectable and actually meant to be so. If there is any more general meaning to the Circuit ID type of 0 and Remote ID type of 0 as used currently by Cisco DHCP Snooping I would like to know if myself (including the other possibilities) but otherwise, all these values are purely at the vendor's discretion because no other device is going to parse them.

Does this help a bit? Please feel welcome to discuss further!

Best regards,

Peter

Bronze

Re: Remote id suboption in dhcp option 82

Hey,Thanks Peter.That helped a lot.

2009
Views
5
Helpful
2
Replies