Administrator’s Handbook
72
Application Layer Gateway (ALG) commands
These commands allow you to enable or disable the router’s support for a variety of Application Layer Gateways
(ALGs). An application layer gateway (ALG) is a NAT component that helps certain application sessions to pass
cleanly through NAT. Each ALG has a slightly different function based on the particular application’s protocol-spe-
cific requirements.
An internal client first establishes a connection with the ALG. The ALG determines if the connection should be
allowed or not and then establishes a connection with the destination computer. All communications go through
two connections – client to ALG and ALG to destination. The ALG monitors all traffic against its rules before decid-
ing whether or not to forward it. The ALG is the only address seen by the public Internet so the internal network is
concealed. In some situations, it may be desirable to disable some of the ALGs.
set ip alg ftp [ on | off ]
Turns the FTP (File Transfer Protocol) ALG for file transfers
on
or
off
. Default is
on
.
set ip alg h323 [ on | off ]
Turns the H323 ALG for audio, video, and data communications across IP-based networks
on
or
off
. Default is
on
.
set ip alg pptp [ on | off ]
Turns the PPTP (Point-to-Point Transfer Protocol) ALG for authentication
on
or
off
. Default is
on
.
set ip alg sip [ on | off ]
Turns the SIP (Session Initiation Protocol) ALG for voice communication initiation
on
or
off
. Default is
on
.
set ip alg tftp [ on | off ]
Turns the TFTP (Trivial File Transfer Protocol) ALG for simple file transfers and firmware updates
on
or
off
.
Default is
on
.
Link commands
link
s represent physical connections. Currently, port-based VLAN support is provided at this level.
set link name
name
type [ ethernet... ]
Specifies whether the
type
of the
link
named
name
is
ethernet
or some other.
(
ethernet
is the only
type
currently. Subsequent releases will support various PPP cases.)
set link name
name
igmp-snooping [ off | on ]
Turns
igmp-snooping
off
or
on
on the
link
named
name
.
set link name
name
port-vlan ports [ lan | ptm | vc-1 | vc-2 ]
Specifies a port-based VLAN on the selected ports on the
link
named
name
.
set link name
name
port-vlan priority [ 0 - 7 ]
Specifies the 802.1p priority bit. If you set this to a value greater than 0, all packets of this VLAN with unmarked
priority bits (pbits) will be re-marked to this priority.
Summary of Contents for Netopia
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