RE: spantree's error posted 08/26/2004
Did you WANT them to trunk? If you put the other side in 802.1Q trunking
mode, then that's the error you'll receive. You could, on your 3750, use
"switchport trunk encapsulation dot1q" to alleviate the issue.
Otherwise, if you want them to be access ports, specify it.
According to 3750 docs, the default mode is negotiate for encapsulation, but
"If you enter the negotiate keywords and DTP negotiation does not resolve
the encapsulation format, ISL is the selected format. The no form of the
command resets the trunk encapsulation format to the default."
"Recommended Action Verify that the configuration and operational state
of the listed interface and that of the interface to which it is connected
are in the same mode (access or trunk). If the mode is trunk, verify that
both interfaces have the same encapsulation (none, ISL, or 802.1Q). When
these parameters are consistent, spanning tree automatically unblocks the
So perhaps the theory of DTP negotiation between a 2950 and 3750 doesn't
follow the same standard. There's nothing in the 2950 docs about
encapsulation negotiaion, just whether or not you're a trunk.
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIP, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of Tom
Sent: Thursday, August 26, 2004 1:40 AM
Subject: spantree's error
I connect a Cat3750 and Cat2950 with one RJ45 cable.
Next error occured.
SPANTREE-7-RECV_1Q_NON_TRUNK: Received 802.1Q BPDU on non trunk [chars]
I don't set anything one Cat2950.For the Cat3750's interface, I input the
description " Access 192.168.45.0/24 NW "
switchport access vlan 45
no ip address
no mdix auto
3750G#show int g1/0/11 switchport
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate Operational Trunking
Encapsulation: native Negotiation of Trunking: On Access Mode VLAN: 45
(NOTES) Trunking Native Mode VLAN: 1 (default) Voice VLAN: none
Administrative private-vlan host-association: none Administrative
private-vlan mapping: none Administrative private-vlan trunk native VLAN:
none Administrative private-vlan trunk encapsulation: dot1q Administrative
private-vlan trunk normal VLANs: none Administrative private-vlan trunk
private VLANs: none Operational private-vlan: none Trunking VLANs Enabled:
ALL Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none
Why the error happened? Why they couldn't negotiate it?
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