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cisco 881 xconnect performance

I'm looking for the limits on a l2tpv3 xconnect layer2 connection of the cisco 881 by means of a lab setup.

2 cisco 881 directly connected to each other with their Fa4

the Fa3 in a vlan, with the vlan interface xconnected to the other cisco. ipsec is not used yet

so far I learned that fragmentation takes down the receiving cisco (who was to defragment the packet).

If I lower the MTU on the testing pc (connected to Fa3), I get full 100mbit performance.

If I raise the MTU of both the Fa4 interfaces (something I am suprised is possible, since this is not gig) I get 50 mbit performance. And I wonder why, because the cisco is not doing fragmentation anymore, (confirmed in debug).

Does the cisco switch back to cpu performance instead of HW performance is you raise the MTU?

how do you explain the possibility of raising the MTU on a Fa interface?

using  Version 15.2(2)T in adv ip services licencing (trial)

relevant config, reason why choosen manual l2tp is becauce once working like expected, one cisco is going to be replaced by linux

pseudowire-class l2tpv3

encapsulation l2tpv3

interworking ethernet

protocol none

ip local interface FastEthernet4

interface FastEthernet4

mtu 2000

ip address

ip mtu 1980

ip virtual-reassembly in

load-interval 30

duplex auto

speed auto

interface FastEthernet3

switchport access vlan 100

no ip address

interface Vlan100

no ip address

no autostate

xconnect 30 encapsulation l2tpv3 manual pw-class l2tpv3

  l2tp id 1 1

  l2tp cookie local 4 0

  l2tp cookie remote 4 0

kind regards


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