Protocol Details - Allied Telesis AT-8600 Series How To Use Manual

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:
The sub-options within the DHCP option are constructed as follows:
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
1
2
6
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:
0010:
0020:
Page 9 | AlliedWare™ OS How To Note: DHCP Snooping on Rapier-style switches
Code Len Agent Information Field
+------+------+------+------+------+------+---+------+
| 82 | N | i1
+------+------+------+------+------+------+---+------+
SubOpt Len Sub-option Value
+------+------+------+------+------+------+---+------+
| 1 | N | s1
+------+------+------+------+------+------+---+------+
SubOpt Len Sub-option Value
+------+------+------+------+------+------+---+------+
| 2 | N | i1
+------+------+------+------+------+------+---+------+
RFC Description
RFC 3046 Agent Circuit ID sub-option – used for defining the switch port and
VLAN number of the port user(s).
RFC 3046 Agent Remote ID sub-option – used for defining the MAC address of
the switch that added the Option 82 information.
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.
52 20 01 06 00 04 00 30 00 05
CD 11 B2 52 06 0C 55 73 65 72 49 64 30 31 32 33
34 35
| i2 | i3 | i4
| s2 | s3 | s4
| i2 | i3 | i4
02 08 00 06 00 00
DHCP Option 82
| | iN |
| | sN |
| | iN |
R ..............
...R..UserId0123
45