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VLAN Status Confusion

I have several vlans running on a 4510R, but I have confusion on one of them.

When I do a sh vlan brief everything looks fine, the vlan in question (vlan99) is active and has 4 ports assigned to it. When I do a sh int desc, however, vlan99 shows 'admin down/down' for status and protocol. Yet, if I ping from the interface on the device connected to the vlan to another device on the same vlan, I get no packet loss; all pings succeed.

If the vlan is active and passing traffic, why doe sthe sh int desc show it as 'admin down/down' when all my other vlans are shown a up/up? 

4 ACCEPTED SOLUTIONS

Accepted Solutions

VLAN Status Confusion

Can you paste the output? Is it possible that the SVI is shutdown? But you were pinging with that IP as a source? Are you sure it was using that IP as the outgoing IP?

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
Hall of Fame Super Gold

VLAN Status Confusion

I agree that the SVI which is interface vlan 99 has been shut down. And the layer 2 vlan is active and forwarding frames. My understanding of the post is that one PC in vlan 99 is able to ping another PC in vlan 99. And that is quite logical if the layer 2 vlan is active and forwarding frames.

I think the main confusion in the original post is the relationship between the layer 3 SVI of interface vlan 99 and the layer 2 performance of vlan 99.

HTH

Rick

Super Bronze

Re: VLAN Status Confusion

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

I believe Rick has explained the situation - in other words, a SVI (i.e. a VLAN interface) is unnecessary (or be active) for two hosts on the same VLAN to communicate with each other.

Purple

VLAN Status Confusion

  Right as the rest have said you have some confusion between a layer 2 vlan and the layer 3 SVI status .  Devices will still talk if they are on the same vlan even with the layer 3 svi in a down status , they just cannot talk to devices in different vlans if the the layer 3 SVI is down.

8 REPLIES

Re: VLAN Status Confusion

Hi,

"show interface description" shows the status of the SVI, "show vlan [brief]" the (layer-2) VLAN.

I'm not sure if you can remove the SVI config with "no interface vlan99" on a 4500 if you don't need it.

[EDIT] :

What status does a "show ip interface brief vlan 99" show?

HTH

Rolf

Hall of Fame Super Blue

VLAN Status Confusion

Matthew

Can you clarify what you mean by -

if I ping from the interface on the device connected to the vlan to another device on the same vlan, I get no packet loss; all pings succeed.

do you mean ping from 4510R to a device in vlan 99 or ping from a device in vlan 99 to another device in vlan 99 ie. PC to PC for example ?

Jon

VLAN Status Confusion

Can you paste the output? Is it possible that the SVI is shutdown? But you were pinging with that IP as a source? Are you sure it was using that IP as the outgoing IP?

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
Hall of Fame Super Gold

VLAN Status Confusion

I agree that the SVI which is interface vlan 99 has been shut down. And the layer 2 vlan is active and forwarding frames. My understanding of the post is that one PC in vlan 99 is able to ping another PC in vlan 99. And that is quite logical if the layer 2 vlan is active and forwarding frames.

I think the main confusion in the original post is the relationship between the layer 3 SVI of interface vlan 99 and the layer 2 performance of vlan 99.

HTH

Rick

Super Bronze

Re: VLAN Status Confusion

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

I believe Rick has explained the situation - in other words, a SVI (i.e. a VLAN interface) is unnecessary (or be active) for two hosts on the same VLAN to communicate with each other.

Purple

VLAN Status Confusion

  Right as the rest have said you have some confusion between a layer 2 vlan and the layer 3 SVI status .  Devices will still talk if they are on the same vlan even with the layer 3 svi in a down status , they just cannot talk to devices in different vlans if the the layer 3 SVI is down.

New Member

VLAN Status Confusion

Rich re-stated my confusion accurately. Sorry for not explaning my problem better!

Joe and Glen's information for the SVI being unecessary for the two hosts to communicate cleared my confusion. With the SVI for vlan99 shutdown, the two hosts will not be able to talk to different vlans, which is the desired configuration.

Thanks for clearing up my confusion! Correct answers have been applied.

Hall of Fame Super Gold

VLAN Status Confusion

I am glad that we were able to help you understand the issue here and to find a solution that gave the results that you wanted. Thank you for using the rating system to mark multiple answers as correct answers.

HTH

Rick

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