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The mesh config and deployment guides state:
“The RAP must always connect to the native VLAN ID 1 on a switch. The RAP's primary Ethernet interface is by default the
native VLAN of 1. “
http://www.cisco.com/en/US/docs/wireless/technology/mesh/7.0/design/guide/MeshAP_70.html#wp1749968
http://www.cisco.com/en/US/docs/wireless/controller/7.0MR1/configuration/guide/cg_mesh.html#wp1858032
Why does it matter?
Let’s closely and methodically look at an initial config with ethernet bridging with a single Rap and Map, both with an attached
switch.
New configuration. Rap and Map joined to WLC. Map child of Rap. Here’s all we’ve done so far:
•
configured Rap’s switchport as mode trunk, native vlan 31
•
configured Map’s switchport as mode trunk. No native vlan config, therefore native vlan is 1.
•
Disabled Vlan transparent on the controller
•
Enabled ethernet bridging on the rap and the map
•
We intend to next configure the map’s ethernet port for vlan tagging (trunk or access), but we’re already broken.
•
The key point is that upon enabling ethernet bridging on a Mesh AP, the initial ethernet interface mode is Normal. This mode
behaves as if vlan transparent were enabled, and the native vlan of the Rap’s switch port *is* forwarded out of the Map’s ethernet
interface untagged.
RAP 802.11a
5Ghz radio MAP
1242-A 1242-B
Fas0 interface Gig0/5 Fas0
switchport trunk encap dot1q interface GigabitEthernet0/6
switchport mode trunk switchport trunk encapsulation dot1q
switchport trunk native vlan Gig 0/6 switchport mode trunk
31
G0/5 %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent
peer vlan id 1 on GigabitEthernet0/5 VLAN31. 3560-B
%SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/5 on
VLAN0001. Inconsistent peer vlan.
%SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/5 on
3560-A VLAN0031. Inconsistent local vlan.
G0/25 3560-A#sho span int gig 0/5
Vlan Role Sts Cost Prio.Nbr Type
Port1 ------------------- ---- --- --------- --------
-------------
VLAN0001 Desg BKN*19 128.5 P2p
4400-A *PVID_Inc
VLAN0031 Desg BKN*19 128.5 P2p
*PVID_Inc
Since switch 3560-A’s native vlan 31 BPDU's are being received on switch 3560-B’s port untagged (which 3560-B expects to be Vlan 1),
and vise versa, both switches will perpetually churn spanning tree state for the relevant vlans.
The Rap and Map will sporadically drop and rejoin the controller. The AP’s will intermittently display in the WLC’s gui and appear
configurable.
During this unstable state, you may be able to configure the map’s ethernet interface as a trunk, but the config will unlikely be applied if
the Rap and or Map are in the process of losing connectivity due to the spanning tree misconfig. Although it appears as though you may
have successfully configured the Map’s ethernet interface as a trunk, it will likely lose connectivity to the controller, and return in Normal
mode, which will continue the unstable state.
interface Gig 0/5
switchport trunk encap dot1q
switchport mode trunk
switchport trunk native vlan 31
RAP 802.11a
5Ghz radio MAP
1242-A 1242-B
interface GigabitEthernet0/6
switchport trunk encapsulation dot1q
Fas0 Fas0 switchport mode trunk
Gig 0/6
G0/5
3560-B
3560-A
G0/25 %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent
peer vlan id 1 on GigabitEthernet0/5 VLAN31.
Port1 %SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/5 on
VLAN0001. Inconsistent peer vlan.
%SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/5 on
VLAN0031. Inconsistent local vlan.
4400-A
3560-A#sho span int gig 0/5
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------
interface GigabitEthernet0/25 VLAN0001 Desg BKN*19 128.5 P2p *PVID_Inc
switchport trunk encap dot1q
switchport mode trunk VLAN0031 Desg BKN*19 128.5 P2p *PVID_Inc
This condition is caused by the switches’ protective mechanism that detects the spanning tree BPDU vlan identifier is mismatched:
To simplify and clarify this concept, let’s see what happens when we take mesh out of the picture with the same switched topology…
same result.
RAP 802.11a MAP
5Ghz radio
1242-A 1242-B
1.1.1.66 1.1.1.64
Fas0 Fas0
interface GigabitEthernet0/6
switchport trunk encapsulation dot1q
switchport mode trunk
G0/5 Gig 0/6
3560-A interface Gig0/5
switchport trunk encap dot1q 3560-B
switchport mode trunk
switchport trunk native vlan 31
%LINK-3-UPDOWN: Interface GigabitEthernet0/6, changed state to up
%SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan id 31 on
GigabitEthernet0/6 VLAN1.
%SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/6 on VLAN0031. Inconsistent peer vlan.
%SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/6 on VLAN0001. Inconsistent local
vlan.
3560-B#show span int gig 0/6
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------
VLAN0001 Desg BKN*4 128.6 P2p *TYPE_Inc
VLAN0031 Desg BKN*19 128.5 P2p *PVID_Inc
%LINK-3-UPDOWN: Interface GigabitEthernet0/5, changed state to down
%LINK-3-UPDOWN: Interface GigabitEthernet0/5, changed state to up
%SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan id 1 on
GigabitEthernet0/5 VLAN31.
%SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/5 on VLAN0001.
Inconsistent peer vlan.
%SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/5 on VLAN0031.
Inconsistent local vlan.
3560-A#sho span int gig 0/5
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- ------------------
VLAN0001 Desg BKN*4 128.5 P2p *PVID_Inc
VLAN0031 Desg BKN*4 128.5 P2p Edge *PVID_Inc
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