Reducing the packet length

The length reduction of the data packets is defined by a Firewall rule according to the following conditions:

The reduction refers to all packets, which will be sent to the interface and which do not correspond to the rule.
Not packets of certain protocols are reduced, rather than all packets globally on that interface

For LANCOM devices with VoIP functions that were already integrated or added in with a software option, fragmentation and PMTU reduction can be set separately for SIP calls.

For configuration with WEBconfig or Telnet, the reduction is entered in a new Firewall rule by parameter “P” for PMTU reduction (Path MTU, MTU = Maximum Transmission Unit) and “F” for the fragment size.

LANconfig: Firewall/QoS / Rules / Filter rules / Quality of Service

WEBconfig: Setup / IP router / Firewall / Rule list

Note: PMTU reduction and fragmentation refer always to the physical connection. Indicating parameter “W” for WAN sending direction is not required here and hence will be ignored if existing.

The following example shows a setting for Voice over IP telephony:

Rule	Source	Destination	Action	Protocol
VOIP	IP addresses of IP telephones in the LAN, all ports	IP addresses of IP telephones in the LAN, all ports	%Qcds32 %Prt256	UDP

This rule defines the minimum bandwidth for sending and receiving to 32 Kbps, forces and reduces the PMTU while sending and receiving to packets of 256 byte size. For the TCP connection, the maximum segment size of the local workstation is determined to 216, so that the server will send packets of maximum 256 byte (reduction of the PMTU in sending and receiving direction).