From: Roberts, Larry (Larry.Roberts@expanets.com)
Date: Wed Aug 27 2003 - 00:32:19 GMT-3
Just to add my .02
First, the Native VLAN is 1 on all ports, unless otherwise specified.
(e.q. switchport access vlan 2)
I also don't see Switch 1's port 20 configuration in your configs?
Im going to assume it looks like such
interface FastEthernet0/20
switchport mode access
no ip address
--> Notice the lack of "switchport access vlan 2" meaning it defaults to
vlan 1
With Trunk ports:
The Native VLAN is what VLAN the switch will put any untagged packets it
recieves into.
While I don't remember where I read it, I also believe that any packets that
are in that VLAN are sent between two trunk ports without being tagged.
I suspect as a way to save BW, but that's a guess.
This error is just the switch saying that " Hey, were are going to cross
talk on VLAN's because your sending me untagged packets from your VLAN X,
and I put them into my VLAN Y"
Considering plain old access ports:
On F0/20 on both routers, change the native vlan ( switchport access vlan 2
) so that they both match and the error will go away.
Or , just turn off CDP. Since these are access ports, no VLAN info is
carried in the packets. And the switchs wouldn't know that they each had a
different native VLAN
Make sense, or did I miss your question?
Thanks
Larry
-----Original Message-----
From: Jonathan V Hays [mailto:jhays@jtan.com]
Sent: Monday, August 25, 2003 2:39 PM
To: boby2kusa@hotmail.com; ccielab@groupstudy.com
Subject: RE: Cat3550: ISL native VLAN mismatch?
Hi,
Yes, both fa0/19 and fa0/20 are connected via crossover and I realize that
the default port mode is dynamic desirable.
Thanks for pointing out that this error probably has nothing to do with the
ISL trunk on fa0/19. So I guess what you are saying is that if I configure
one side for "switchport mode access" then the other side won't like it,
since it is still in dynamic mode trying to trunk? That makes sense.
But I'd still like to understand clearly what the reference to a "Native
VLAN" is all about in that error message.
Here's a wild guess.
By default the Native VLAN is 1 on the dynamic desirable unconfigured port,
which it evidently makes a point of advertising to the other side. When you
lock the other side to VLAN 2 (access mode), the unconfigured port gets
upset because its former "trunk-mate" won't advertise VLAN 1 any more.
Well, it's a theory, anyway.
Any thoughts?
-----Original Message-----
From: boby2kusa@hotmail.com [mailto:boby2kusa@hotmail.com]
Sent: Monday, August 25, 2003 3:05 PM
To: Jonathan V Hays; ccielab@groupstudy.com
Subject: Re: Cat3550: ISL native VLAN mismatch?
jonathan,
The error seems to be on fa0/20 on both the switches NOT fa0/19:
00:19:24: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered
> on FastEthernet0/20 (2), with S1_3550 FastEthernet0/20 (1).
These devices have trunking on desirable by default check the S1_3550 if
it's trunking.
----- Original Message -----
From: "Jonathan V Hays" <jhays@jtan.com>
To: <ccielab@groupstudy.com>
Sent: Monday, August 25, 2003 11:44 AM
Subject: FW: Cat3550: ISL native VLAN mismatch?
> All,
>
> While playing around with Emad's config (see "Cat3550: strange
problem")
> I came across an unexpected error message:
>
> "00:19:24: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch
discovered
> on FastEthernet0/20 (2), with S1_3550 FastEthernet0/20 (1)."
>
> Physically, ports fa0/19 and fa0/20 are connected between two Catalyst
> 3550 switches with crossover cables. I configured fa0/19 as an ISL
> trunk. I then configured fa0/20 on switch 2 (S2_3550) with VLAN 2 and
> got the error.
>
> I thought 'native vlan' applied only to Dot1Q trunks. Evidently not. I
> guess I need to reread the switch software configuration guide.
>
> A minute later I remembered that configuring a port with vlan 2 was
not
> necessary for what I was trying to accomplish so I removed it from
> fa0/20. All I needed to do was to create the VLAN. The command
> "interface vlan 2" does not create a VLAN, although "switchport access
> vlan 2" does create a VLAN. And of course you can simply create the
vlan
> without applying it to an interface, using either "config-vlan Mode"
or
> "VLAN Configuration Mode", as Cisco calls them. I think Cisco could
have
> created more distinctive terms for these two modes.
>
> Here's the link for those unfamiliar with these two modes:
>
>
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12114ea1/3550s
> cg/swvlan.htm#1196935
>
> Does anyone have an insight into the cause of this error message?
>
>
> No VLANs had been created at this point and the configs were as
follows:
>
> SWITCH 1:
> =========
> interface FastEthernet0/19
> switchport trunk encapsulation isl
> switchport mode trunk
> no ip address
> !
> interface Vlan2
> ip address 20.1.1.1 255.255.255.0
> !
> interface Vlan3
> ip address 30.1.1.1 255.255.255.0
> !
> ip default-gateway 20.1.1.2
> ip classless
>
> SWITCH 2:
> =========
> interface FastEthernet0/19
> switchport trunk encapsulation isl
> switchport mode trunk
> no ip address
> !
> interface FastEthernet0/20
> switchport access vlan 2
> switchport mode access
> no ip address
> !
> interface Vlan2
> ip address 20.1.1.2 255.255.255.0
> =========
> AFTER CONFIGURING FA0/20:
> =========
> S2_3550(config)#in fa0/20
> S2_3550(config-if)#switchport mode access
> S2_3550(config-if)#switchport access vlan 2 % Access VLAN does not
> exist. Creating vlan 2 S2_3550(config-if)#
> 00:19:24: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered
> on FastEthernet0/20 (2), with S1_3550 FastEthernet0/20 (1).
> S2_3550(config-if)#
> 00:19:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan2,
changed
> state to up
> S2_3550(config-if)#
> 00:20:24: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered
> on FastEthernet0/20 (2), with S1_3550 FastEthernet0/20 (1).
> S2_3550(config-if)#
>
> The same error message appeared on the other switch.
>
> Thanks for your comments,
>
> Jonathan
>
>
>
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