CDRouter Support

Does CDRouter automatically handle fragmented IP packets?

knowledge-base version 13.3

In general, CDRouter assumes that the largest size IPv4 packet that can be transmitted without fragmentation is known. CDRouter uses this information to transmit maximum size packets while avoiding fragmentation. Test case failures may occur in instances where there is a mismatch between the DUT’s maximum MTU and CDRouter’s configured MTU.

How can I avoid fragmentation?

IPv4 fragmentation can be avoided by properly configuring the lanMtu testvar. CDRouter’s testvar lanMtu defines the maximum IPv4 MTU for any LAN client. If set to default, CDRouter will automatically determine the maximum MTU that can be supported without IP fragmentation based on the configured WAN protocol:

WAN Mode Default lanMtu Value
static 1500
DHCP 1500
PPPoA 1500
PPPoE 1492
PPTP 1460
L2TP 1460
PPP/T1 1500

CDRouter’s lanMtu testvar should always match the maximum MTU on the DUT. For example, if the DUT’s MTU on the WAN side is 1000, the lanMtu should also be set to 1000:

testvar lanMtu      1000

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