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Monday, June 4, 2012

Router on a stick: 2811 with 3750, not propagating VLANs


We are trying to configure router on a stick with 2811 and 3750, but we just cannot get it to work - vlans are not getting propagated from 3750 to 2811:
 
3750:
 
interface FastEthernet1/0/48
switchport trunk encapsulation dot1q
switchport trunk native vlan 100
switchport mode trunk
speed 100
duplex full
...
 
3750#sh vtp s
VTP Version                     : running VTP2
Configuration Revision          : 1
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 8
VTP Operating Mode              : Server
VTP Domain Name                 : NULL
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0xEC 0x70 0xEB 0x0B 0x7D 0xC0 0xC4 0xDE
Configuration last modified by 192.168.1.205 at 3-2-93 18:33:32
Local updater ID is 192.168.1.205 on interface Vl1 (lowest numbered VLAN interface found)
3750#sh vtp c
VTP statistics:
Summary advertisements received    : 0
Subset advertisements received     : 0
Request advertisements received    : 0
Summary advertisements transmitted : 73
Subset advertisements transmitted  : 7
Request advertisements transmitted : 0
Number of config revision errors   : 0
Number of config digest errors     : 0
Number of V1 summary errors        : 0
 
VTP pruning statistics:
 
Trunk            Join Transmitted Join Received    Summary advts received from
                                                   non-pruning-capable device
---------------- ---------------- ---------------- ---------------------------
Fa1/0/46            0                0                0      
Fa1/0/48            0                0                0
 
3750#sh int fa1/0/48 switchport
Name: Fa1/0/48
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 100 (SERVER)
Administrative Native VLAN tagging: enabled
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 Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
 
Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none
3750#
 
2811:
 
interface FastEthernet0/0
no ip address
duplex full
speed 100
!
interface FastEthernet0/0.1
encapsulation dot1Q 100 native
!
interface FastEthernet0/0.2
encapsulation dot1Q 102
!
interface FastEthernet0/0.3
encapsulation dot1Q 202
 
2811#sh vtp s
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 36
Number of existing VLANs        : 5
VTP Operating Mode              : Client
VTP Domain Name                 : NULL
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x9A 0xC0 0x5E 0x60 0x9B 0xD6 0xE3 0x98
 
2811#sh vtp c
VTP statistics:
Summary advertisements received    : 0
Subset advertisements received     : 0
Request advertisements received    : 0
Summary advertisements transmitted : 0
Subset advertisements transmitted  : 0
Request advertisements transmitted : 0
Number of config revision errors   : 0
Number of config digest errors     : 0
Number of V1 summary errors        : 0
 
VTP pruning statistics:
 
Trunk            Join Transmitted Join Received    Summary advts received from
                                                   non-pruning-capable device
---------------- ---------------- ---------------- ---------------------------
2811#
 
IOS are 12.4. Tried both VTP1 and VTP2, empty and various domain names, client and transparent modes - all to no avail. I also tried deleting vlan.dat from 2811.


The show vtp commands output on the 2811 router would be interesting only if you had a switching module installed into it and created VLANs on that module. Otherwise, the show vlan-switch or show vtp command output is irrelevant. Also, the router does not speak VTP on its routed ports, that is why the VLANs are not propagating.

What you are creating right now are subinterfaces for selected VLANs. You do that on the 2811 without creating the VLANs explicitly - you simply directly refer to them on the individual subinterfaces.

So what you see is absolutely fine and normal. I am sure that the VLANs themselves work. Do not be worried by the VLANs not propagating from the switch to your router - they are not supposed to be propagated.


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