Is there a way to set the MRU that CDRouter uses for PPP LCP?

The PPP MRU gets set automatically based on the type of WAN protocol that is running. The following default values are used:

  • PPPoE 1492
  • PPPoA 1500
  • PPTP 1460
  • L2TP 1460

There are two ways to modify CDRouter’s default LCP MRU value. The first way is to configure the testvar lanMtu to a value other than default. This changes both the maximum size packet that will be used on the LAN as well as the LCP MRU.

testvar lanMtu 1440

In the above example, the MRU used by PPP LCP will be 1440. As a result, CDRouter will not send packets on the LAN greater than 1440 without IPv4 fragmentation.

The second option for changing the LCP MRU is to explicitly set its value using the testvar pppForceLcpMRU . If this testvar is set, the PPP LCP MRU with be set based on the this value regardless of the lanMtu setting. This can be a work around for routers that will not negotiate a LCP MRU less than 1500 bytes.

testvar pppForceLcpMRU  1500