ELTEX LTP-4X, Operation Manual

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Chapter 22.
DHCP Relay Agent Configuration
Introduction
This chapter describes configuration of DHCP Relay Agent in the terminal.
DHCP Relay Agent is used to provide a DHCP server with additional information about a received DHCP
request. This may include information about the terminal running DHCP Relay Agent as well as information
about the ONT, which sent the DHCP request. DHCP packets are modified by interception and further
processing in the terminal CPU.
The DHCP server analyses DHCP option 82 and identifies the ONT. DHCP Relay Agent allows the option to
be both transparently transmitted from the ONT and formed/rewritten according to a specified format.
DHCP option 82 is especially useful for networks, which have no private VLANs dedicated for each user.
DHCP Relay Agent supports configurable formats for both Circuit ID and Remote ID. The format of the
suboptions is configured with the help of the tokens listed in Table 22.1. The placeholders will be replaced
with corresponding values, while the rest of the words will be passed as is.
Table 22.1 – DHCP Option 82 Tokens
Token
Description
%HOSTNAME% Terminal network name
%MNGIP%
Terminal IP address
%GPON-PORT% Number of the OLT channel the DHCP request arrived from
%ONTID%
ID of the ONT, which sent the DHCP request
%PONSERIAL% Serial number of the ONT, which sent the DHCP request
%GEMID%
ID of the GEM port the DHCP request arrived to
%VLAN0% External VID
%VLAN1% Internal VID
%MAC% MAC address of the ONT, which sent the request
%OLTMAC% OLT`s MAC address
%OPT60% DHCP option 60 received from the ONT
%OPT82_CID% Circuit ID received from the ONT
%OPT82_RID% Remote ID received from the ONT
%DESCR%
First 20 characters of ONT description
In addition to DHCP option 82, DHCP Relay Agent has some more functions related to network security. It
provides protection from DoS attacks by setting a threshold for intensity of DHCP messages, which are
received from ONT. Exceeding the threshold blocks DHCP requests. The blocking time can be configured.