Configuring Maximum Transmission Unit Size; Adsl Interface In Screenos Devices - Juniper NETWORK AND SECURITY MANAGER 2010.4 - CONFIGURING SCREENOS DEVICES GUIDE REV 01 Manual

Configuring ScreenOS Devices Guide

Configuring Maximum Transmission Unit Size

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ADSL Interface in ScreenOS Devices

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The MTU size option is only supported by some security devices. As packets traverse
different networks, a networking component sometimes needs to break a packet into
smaller pieces (fragments) based upon the maximum transmission unit (MTU) of each
network. The networking component for the destination network must then reassemble
the received fragments into a packet. Because fragmentation and reassembly can impact
network performance, you might want to fragment a packet destined for a VPN tunnel
as it passes through the tunnel interface (before the packet is encrypted and/or
encapsulated).
For devices running ScreenOS 5.1 and later, you can define an MTU size that controls the
size of packets sent through the tunnel. When the tunnel interface receives the packet,
it breaks the packet into fragments based on the specified MTU size, encrypts and/or
encapsulates each fragment, and then sends the traffic through the tunnel. As these
packets (fragments) pass through other networks, they might be small enough that
networking components do not need to perform further fragmentation—which reduces
the network load and can decrease the time it takes to send VPN traffic. The receiving
networking component (security device or external device) must still reassemble the
fragments as they exit the other end of the VPN tunnel.
To configure an MTU size for a tunnel interface, in the tunnel interface navigation tree,
select Advanced Properties and enter a value for MTU Size. By default, the size is set to
none (the interface does fragment packets entering a VPN tunnel). The acceptable range
is from 800 to 1500.
Setting Interface Properties Using the General Properties Screen on page 53
Interface Network Address Translation Methods on page 62
Example: Configuring a WAN Interface (NSM Procedure) on page 86
An asymmetric digital subscriber line (ADSL) is a digital subscriber line (DSL) technology
that enables existing telephone lines to carry both voice telephone service and high-speed
digital transmission. To use ADSL with a security device, you must configure the adsl1
interface on the NetScreen-5GT ADSL security device (which supports ADSL).
Setting Interface Properties Using the General Properties Screen on page 53
ADSL, ADSL Interface, and ADSL Settings in ScreenOS Devices on page 89
Copyright © 2010, Juniper Networks, Inc.