My problem with tunnelling is as follows:
I need to create a layer 2 tunnel with an mtu of 1500 (normal Ethernet), as I
need to be able to tunnel PPPoE with a default MTU.
I have tried to create an L2TPv3 psuedowire for the tunnel. However the overhead
on the tunnel meant the PPPoE packets became too large.
To get around this I have tried running the tunnel over a GRE tunnel with the
mtu increased using the "ip mtu" command. This doesn't seem to work and packets
through the pseudowire seem to get invisibly dropped.
I am unable to increase the MTU on the network inbetween as the network is not
in our control. Are there any better ways of doing this that you know of?
The configuration I am using at both ends is like this:
!
pseudowire-class etherpw
encapsulation l2tpv3
ip local interface Tunnel0
!
interface Tunnel0
ip address 10.2.1.2 255.255.255.252
ip mtu 1600
tunnel source Loopback0
tunnel destination 87.248.130.11
!
interface Loopback0
ip address 87.248.130.10 255.255.255.255
!
interface FastEthernet0
description LAN Interface
no ip address
no ip redirects
no ip proxy-arp
speed auto
no cdp enable
!
interface FastEthernet0.102
encapsulation dot1Q 102
no snmp trap link-status
no cdp enable
xconnect 10.2.1.1 102 pw-class etherpw
I forgot to mention that the tunnel was working, but only when packets exceeded
an mtu of 1436. I use the "ip mtu 1600" to artificially increase packet size so
the L2TPv3 tunnel headers + contents of size 1500 fitted in the GRE tunnel. The
tunnel will still function with "ip mtu 1400", but not with the size of packets
we are using.
What do I need to do to get this working properly?
*Note that this is a personal issue not related to my day job.
thanks
Paul
