L2protocol-Tunneling Sanity Check

Hey everybody, I could use some assistance validating my sanity in this
situation. First, the topology

R1 --- Cat1---Cat2---R2

I am attempting to configure l2protocol-tunneling alone (without Q-Q at
all) such that R1 and R2 see each other as directly connected in CDP. I
thought for sure I had this configuration correct, but it wouldn't work.
Cat1 is a 3560 and Cat2 is a 3550. I am noticing behavior on the 3550 that
is not happening on the 3560. Note there are no trunks and every port is an
access port in VLAN 1.

My original thought was this: configure "no cdp enable" and
"l2protocol-tunnel cdp" on ONLY the edge ports of Cat1 and Cat2 that
connect to the routers. When I do this I see Cat1 encapsulating frames in
"show l2protocol-tunnel" but Cat2 never shows any decapsulated or
encapsulated frames. When R1 sends a CDP frame, Cat1 should intercept it
due to the l2protocol-tunnel CDP command, and rewrite the destination MAC
to the proprietary Cisco MAC used for l2protocol-tunneling. That frame
should then be sent out the cross switch link to Cat2. Cat2 should see
that it also has "l2protocol-tunnel cdp" configured on the edge port facing
R2 and rewrite the destination MAC back to the CDP multicast address and
forward to R2. The same should happen the other way.

Again, the 3560 shows frames encapsulated but the 3550 does not yet they
have an identical configuration. First this led me to believe maybe an IOS
bug in the 3550 12.2(44SE6) so I tried another version with the same
results. Every example I can find out there usually only does l2pt on a
single switch or if spanning multiple switches they are combining with
Q-Q. I understand those concepts fine, but I am not looking to do Q-Q in
this example. I don't have another 3560 on hand to test with.

I started second guessing myself and thinking I needed "l2protocol-tunnel
cdp" on the edge ports AND the cross switch links on both ends. When I do
that, it actually works but I don't think it works for the right reasons.
Ultimately, in this type of setup can anybody confirm weather you need
"l2protocol-tunnel" on ALL ports between the source and destination or just
on the edge ports.

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
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