Communication problem between ASA 5510 and Cisco 3750, L2 Decode drops

Question

Having problem with communication between ASA 5510 an Cisco Catalyst 3750.
Here is the Cisco switch port facing the ASA 5510 configuration:
interface FastEthernet2/0/6
description Trunk to ASA 5510
switchport trunk encapsulation dot1q
switchport trunk native vlan 50
switchport trunk allowed vlan 131,500
switchport mode trunk
switchport nonegotiate
And here is the ASA 5510 port configuration:
interface Ethernet0/3
speed 100
no nameif
no security-level
no ip address
interface Ethernet0/3.500
vlan 500
nameif outside
security-level 0
ip address X.X.X.69 255.255.255.0
There is a default route on ASA to X.X.X.1.
When I try to ping from ASA X.X.X.1 i get:
Sending 5, 100-byte ICMP Echos to 31.24.36.1, timeout is 2 seconds:
Also in the output of show interface eth 0/3 on the ASA i can see that the L2 Decode drop counter increases.
I have also changed the ports on the Switch and ASA but the same error stays.
Any thoughts?

Answer 1

I don't see anything wrong with your trunk configuration; I have a similar one working between an ASA 5520 and a Catalyst 3750G.
Maybe you should adjust the "speed 100"?  In my experience, partial autoconfiguration results in duplex mis-matches, which results in dropped packets.
I'd try removing the "speed 100" and letting the ASA port autonegotiate with the switch.  Alternatively, have both sides set
   speed 100
   duplex full
and see if things improve.
-- Jim Leinweber, WI State Lab of Hygiene