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Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring DHCP Features (Rev. 03)
DHCP Relay
© 2008 Foundry Networks, Inc.
Page 44 of 63
This feature communicates information to the DHCP server, using a sub-option of the DHCP relay
agent information option called
agent circuit-ID
. The DHCP server can use this information to
make IP address assignments.
Figure 10
shows the format of the virtual circuit-ID on which the DHCP request comes in. The
string is 20 bytes long (15 bytes if the DHCP relay tag was not defined).
1
20 bytes
TAG (5 bytes)
VLAN ID (5 bytes)
Port (10 bytes)
Figure 10: Format of the Virtual Circuit-ID
For example, if the VLAN tag is 20, the port number is 1 and the circuit-ID tag is 23, the result in
the automatic circuit-ID assignment will be as follows:
•
in string format: 00023000200000000001;
•
in hexadecimal format: 30 30 30 32 33 30 30 30 32 30 30 30 30 30 30 30 30 30 30 31.
The circuit-ID can also be defined by the user as a string of characters, for example: Customer1.
The DHCP server will identify the circuit-ID by its name “Customer1”.
Depending on the particular needs, Option 82 may be of binary or ASCII type. Each one of these
types has its variants, which are referred to as sub-options
(see
Figure 11
).
Figure 11: Option 82 and corresponding sub-options
ASCII circuit ID
The format of the ASCII Circuit ID is shown in
Figure 12
.
VLAN ID (5 bytes)
Port (10 bytes)
Figure 12: Format of the ASCII Circuit-ID
Tagged ASCII Circuit ID
Figure 3
shows the format of the tagged ASCII Circuit ID. The tagged ASCII Circuit ID string is
20 bytes long (15 bytes if the DHCP relay tag was not defined).