ZyXEL Communications MSC1000G Series, User Manual

Page: 81 / 1168

Management Switch Card User’s Guide
81
C
H A P T E R
4
Access Control List Screens
This chapter describes the ACL (Access Control List) screens.
4.1 DHCP Relay Overview
DHCP (Dynamic Host Configuration Protocol, RFC 2131 and RFC 2132) allows individual clients to
obtain TCP/IP configuration at start-up from a DHCP server. You can configure the system to relay
client TCP/IP configuration requests to a DHCP server and the server's responses back to the
clients.
You can configure the system to forward client DHCP requests from different VLANs to specific
DHCP servers.
4.1.1 DHCP Relay Agent Information Option (Option 82)
The system can add information to DHCP requests that it relays to a DHCP server. This helps
provide authentication about the source of the requests. You can also specify additional information
for the system to add to the DHCP requests that it relays to the DHCP server. Please refer to RFC
3046 for more details.
The DHCP relay agent information feature adds an Agent Information field to the option 82 field of
the DHCP headers of client TCP/IP configuration request frames that the management switch card
relays to a DHCP server. The MSC supports two formats for the DHCP relay agent information:
Private and TR-101.
4.1.2 Private Format
The DHCP relay agent information feature adds an Agent Information field to the option 82 field of
the DHCP headers of DHCP request frames that the MSC relays to a DHCP server. The Agent
Information field that the MSC adds contains an “Agent Circuit-ID sub-option” that includes the slot
and port numbers, VLAN ID and optional information about the slot and port on which the DHCP
request was received.
The following table shows the format of the private Agent Circuit ID sub-option. The (binary) “1” in
the first field identifies this as an Agent Circuit ID sub-option. The length
N gives the total number
of octets in the Agent Information Field. If the configuration request was received on a DSL port, a
1-byte
Slot No field specifies the ingress slot number, and a 1-byte Port No field specifies the
ingress port number (both in hexadecimal format). The next field is 2 bytes and displays the DHCP
request packet’s VLAN ID. The last field (
A ) can range from 1 to 24 bytes (including a one-byte
termination character) and is optional information (that you specify) about this relay agent.
Table 9
DHCP Relay Agent Circuit ID Sub-option Format: Private
1 N Slot No Port No VLAN ID A