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Cisco Vlan Query

Posted on 2012-04-01
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Last Modified: 2012-08-13
Hi Experts,

Can someone explain to me why I can't see the vlan 100 and name user-vlan in the show run in the first attachment, however I can see it when I do a show vlan brief? However, the second attachment I can see the vlan in the show run/configuration.

The reason why I ask is because when I do a copy the configs from a TFTP to the switch in the first case the vlan 100 and name user-vlan won't be copied to the switch because its not in configuration, whereas in the second case the vlan configurations will be picked up and copied to the switch because its in seen in the configurations

Cheers

Carlton
2012-03-31--12-45-54-164--DLS1-4.txt
2012-03-31--13-37-01-861--DLS1-4.txt
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Question by:cpatte7372
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18 Comments
 
LVL 15

Expert Comment

by:Nayyar HH (CCIE RS)
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There are two methods for vlan configuration; in the vlan database mode and in the config mode;

The first switch looks like the VLAN is configured in VLAN database

example;

vlan database
vlan 100
apply
exit

config t
interface vlan 100
ip address x.x.x.x y.y.y.y
no shut

end
wr mem


The second looks like the VLANs is configured in the config mode

config t

vlan 100

int vlan 100
ip address x.x.x.x y.y.y.y
no shut

end

wr mem




So if you were scripting configuration deployments you would to include appropriate config for vlan configuration
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Author Comment

by:cpatte7372
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Nazsky,

Thanks for responding.

I used conf t in both cases....
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Expert Comment

by:Nayyar HH (CCIE RS)
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Wierd .. are you using real switches or emulation software?
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Author Comment

by:cpatte7372
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Very wierd....

Real switch.

It didn't do a write mem. Would that make any difference?
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Author Comment

by:cpatte7372
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Actually, it shouldn't make any difference because the vlan is shown with whe show vlan brief command
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Expert Comment

by:Kvistofta
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Even if you do "conf t", in some switches the vlans are stored in a separate vlan database, not in running-config. It´s just the way it is. Look for a file called something like flash:/vlan.dat, that contains the vlan database in switches that doesnt store them in running config.

Best regards
Kvistofta
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Expert Comment

by:Nayyar HH (CCIE RS)
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pls post a "show version" output
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Author Comment

by:cpatte7372
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Kvistofta, Nazsky,

I will post the show version in a bit. However, I was wondering if the fact that the running config where there is not vlan info might because on that switch I configured vtp mode transparent, vtp domain switch and vtp pass ccnp?

Just a thought
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Expert Comment

by:Kvistofta
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vtp mode transparent means that the switch doesnt care about vtp information. All vtp-packets coming into the switch is being passed to other switches but the content of the vtp-packets are not being read. That means that for a vtp transparent-switch you need to configure all vlans by hand, locally. And as I said above, either they stay in the running/startup-config or in the separate vlan-database. In both cases you configure (create) vlans in config-mode.

Best regards
Kvistofta
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Expert Comment

by:Nayyar HH (CCIE RS)
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The vtp configuration should not cause the symptoms experienced - to me it appears like a software cosmetic issue/bug than anything
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Author Comment

by:cpatte7372
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Experts,

This is the answer:

Hello Carlton,

 

What you are seeing here is caused by your VTP mode setting. If the VTP mode is set to Transparent then the VLANs are being displayed in the running-config in addition of being also stored in the vlan.dat file. If the VTP mode is either Server or Client, the VLANs are only stored in the vlan.dat file and do not appear in the running config. As you can see, your second configuration obviously contains the vtp mode transparent command.

 

Best regards,

Peter
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Expert Comment

by:Nayyar HH (CCIE RS)
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Any references/links to Cisco documentation that this is the actual behavior?
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Expert Comment

by:Kvistofta
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cpatte7372: That is so untrue. A VTP-transparent switch does NOT get any vlan-information from VTP.

/Kvistofta
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Author Comment

by:cpatte7372
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Is there any experts that agree with Kvistofta?
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Kvistofta earned 500 total points
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If there is someone that does NOT agree with me, in this case they are totally wrong!
First hit when you google "VTP transparent mode":

-----

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094c52.shtml#vtp_modes


Transparent—VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2.


-----
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Author Comment

by:cpatte7372
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Kvistofta

I guess I agree with the Cisco statement. However, the main issue was why the vlan information isn't stored/displayed in the running config when you do a show run?
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Expert Comment

by:Kvistofta
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As I said, some switches and some software-versions stores the vlan-information in a separate vlan-database on flash, other stores them in startup-config. It´s by design. Why? I guess you will never know unless you find the right developer at Cisco. :-)


Best regards
Kvistofta
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Author Closing Comment

by:cpatte7372
Comment Utility
Cheers mate..
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