I have a Cisco 851w that connects to a Catalyst 2950, the Catalyst have a few vlans and a FW that is being the "Router on a stick", the 851w should only be used in VLAN20.
It connects to Fa0/23 on the catalyst which is configured as follows:
description Line to xxx Fa0
switchport access vlan 20
switchport mode access
switchport port-security violation restrict
switchport port-security mac-address sticky
switchport port-security mac-address sticky aaaa.bbbb.cccc
Even though, I got errors in the log:
%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/23 (20), with xxxxx FastEthernet0 (1). (Same errors appear on the 851 log with different direction)
The 851 doesn't really support VLANs, it does have a vlan database but only "supports" VLAN1, although that doesn't really suppose to matter as I don't try to negotiate a trunk between the devices, and even if I was trying, the native vlan for that interface would be VLAN1 as seen in the following output:
sh int fastEthernet 0/23 switchport
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 20 (Wifi-DMZ)
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 Allowed: ALL
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none
Any one has an idea how to "fix" that problem? the error shouldn't appear in the logs
Can you post the config for the interface of your router that connects to fa0/23?
Sure, although nothing special there...
description To yyyy Fa0/23
I supposed that spanning-tree portfast isn't really needed at the router, however it stays the same even if I remove it.
Under interface F0, see if you have the encapsulate option:
encapsulate dot1q 20 native
Take spanning-tree portfast out.
Try this instead:
no ip address
encapsulate dot1q 20 native
Put your ip address under fa0.20 subinterface, and it *should* work.
There is no IP on that interface,
it looks like cisco didn't really know what to do with those interfaces on the 851, they aren't layer-2 capable and neither layer-3 capable,
xxxx(config-if)#ip address 126.96.36.199 255.0.0.0
% IP addresses may not be configured on L2 links.
% Unrecognized command
also no sub interfaces on this one:
% Invalid input detected at '^' marker.
The IP address is configured on BVI1 which is a bridge between VLAN1 & Dot11Radio0.
I attached those interfaces config as well:
ip address 188.8.131.52 255.255.255.0
ip virtual-reassembly max-reassemblies 64
ip tcp adjust-mss 1435
no ip address
no ip virtual-reassembly
bridge-group 1 spanning-disabled
(Tried removing the bridge-group 1 spanning-disabled as well, didn't help)
Any other thoughts?
I can delete interface vlan 1,
but can't delete the vlan itself.
Tried to do that with int vlan1, I configured int vlan20 instead after putting int vlan20 in the bridge-group instead of vlan1 the router lost connectivity through its LAN interfaces.
It's like the Fa0-3 acts like a "stupid" switch, however they are still aware of vlans (I can execute show interfaces switchport, but can't configure them to do anything...) the problem is why they care about native vlan when both sides are configured as access ports.
And even if they were trunk ports, both sides when the show int switchport command issued shows that the native vlan is vlan1.
I have on the Catalyst another port (Gi0/2) that is a trunk and have native vlan 20, but I don't see how it should be related, I did attach it's configuration maybe you will see something I didn't:
description Lint to zzzzz
switchport trunk native vlan 20
switchport mode trunk
ip dhcp snooping trust
You would delete the vlan from:
router# vlan database
That's where you would create your vlan 20 also.
Can't do that, not in vlan db mode and not from global config:
Vlan can not be added. Maximum number of 1 vlan(s) in the database.
xxxxx(vlan)#no vlan 1
A default VLAN may not be deleted.
You're correct. The c850 ISR will not support multiple VLANs nor will it allow Trunking.
On the switch, have you tried making your native VLAN as VLAN 1?
What do you mean "on the switch"?
On the port, although set to access mode, by default the native vlan is 1.
How can you set a native vlan "on the switch"?
As you have bridging enabled on the 851w, it is carrying BPDUs on the link and the 2950 is detecting it as a regular switch where the Vlans must match.
Now, having different Vlans (both in access-mode) shouldn't be a problem with the connection there but CDP is quite picky when it comes to that.
You can either ignore the message (hard to do when filling up your log) or disable CDP at both ends of the link.
OK, I did manage to solve the problem, while looking at the input from the show cdp ne fa0/23 de command I saw that both the switch and the router was on the same VTP domain (although, obviously the cannot share the same database), and it said "Native Vlan: 1 (Mismatch)"
Changing the VTP domain on the router solved the problem and now it says "Native Vlan: 1" - looks like it doesn't care that there is a mismatch.
Regarding the bridging enable - looks like it doesn't matter, I just tried with a Cisco 851 that doesn't have any bridging and had the same "problem", the 851 also sends BPDUs (was confirmed using bpduguard on the port...) although it doesn't run spanning tree. (reports "No spanning tree instances exist." when using the show span command)
However I still can't find out how does CDP decides what is the "native vlan" at the other side (and obviously it decides incorrectly, because as shown by the show int fa0/23 switchport the native vlan is auto set to 1) any ideas regarding that?