With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
lecConfigMaxDataFrameSize
Lan Emulation Client Config Max Data Frame Size
1.3.6.1.4.1.353.5.3.1.1.1.1.6
C3 Maximum Data Frame Size. The maximum data frame size which this client will use the next time it returns to the Initial State. Auto-configuring clients use this parameter in their Configure requests. Manually-configured clients use it in their Join requests. This MIB object will not be overwritten with the new value from a LE_{JOIN,CONFIGURE}_RESPONSE. Instead, lecActualMaxDataFrameSize will be.
Back to LAN-EMULATION-CLIENT-MIB MIB page.
IPHost Network monitor allows you to monitor lecConfigMaxDataFrameSize on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.