Allied Telesis Rapier i Series, AT-8600 Series, AT-8700XL Series Protocol details, Example Packet

DHCP Option 82

Protocol details

In the DHCP packet, the Option 82 segment is organized as a single DHCP option containing one or more sub-options that convey information known by the relay agent. The format of the option is shown below:

Code	Len		Agent Information Field
+------	+------	+	------+	------+	------+------	+---	+	------+
82		N	i1	i2	i3 i4			iN
+------	+------	+	------+	------+	------+------	+---	+	------+

The sub-options within the DHCP option are constructed as follows:

SubOpt	Len		Sub-option		Value
+------	+------	+	------	+------	+------	+------	+---	+------	+
1	N s1			s2	s3 s4			sN
+------	+------	+	------	+------	+------	+------	+---	+------	+
SubOpt	Len		Sub-option		Value
+------	+------	+	------	+------	+------	+------	+---	+------	+
2	N i1			i2	i3 i4			iN
+------	+------	+	------	+------	+------	+------	+---	+------	+

The following table shows a list of the sub-options that are used for identifying the subscriber that the IP address was allocated to:

Sub-option	RFC	Description
1	RFC 3046	Agent Circuit ID sub-option – used for defining the switch port and
		VLAN number of the port user(s).
2	RFC 3046	Agent Remote ID sub-option – used for defining the MAC address of
		the switch that added the Option 82 information.
6	RFC 3993	Subscriber-ID sub-option – optionally configured per port using set
		dhcpsnooping port=x subscriberid=x – can define port customer
		name, or switch name.

Example Packet

The following shows an extract of a DHCP Request packet that includes Option 82 details:

DHCP Message			Type = DHCP				Request
Bootstrap Protocol
Option	82	– Agent Information (Option)
0000:	52	20	01	06	00	04	00 30 00 05	02 08 00 06 00	00	R
0010:	CD 11		B2	52	06	0C	55 73 65 72	49 64 30 31 32	33	...R..UserId0123
0020:	34	35								45

Page 9 AlliedWare™ OS How To Note: DHCP Snooping on Rapier-style switches