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Community Member

What is the voip-null0 interface?

Hi all,

I have just started in a new company and they have WhatsUp Gold monitoring their network.

We have recieved an email alert for a router voip-null0 interface going down for a couple of minutes and then back up again!

I have searched the web but I can't see what the interface is or does....I assume it has something to do with the routers voice capability but I am not sure what or why we would be monitoring it as an interface.

Any light shed on this topic would be greatly appreciated as always

Thanks

David

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Community Member

What is the voip-null0 interface?

Hi David,

According to the book "TcL Scripting for Cisco IOS" "VoIP-Null0 is purely cosmetic and will be enabled when Cisco Express Forwarding (CEF) is turned on".

Hope it helps.

Kind regards,
Andrew C.

Kind regards, Andrew C.
7 REPLIES
Community Member

What is the voip-null0 interface?

Hi David,

According to the book "TcL Scripting for Cisco IOS" "VoIP-Null0 is purely cosmetic and will be enabled when Cisco Express Forwarding (CEF) is turned on".

Hope it helps.

Kind regards,
Andrew C.

Kind regards, Andrew C.
Community Member

What is the voip-null0 interface?

Thanks for the swift response Andrew, much appreciated

What is the voip-null0 interface?

Hi David

voip-null0 is a cosmetic interface and it's automatically enabled  when ip cef is enabled.

HTH

regards

Carlo

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"The more you help the more you learn"

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Community Member

What is the voip-null0 interface?

Thanks for the swift response Carlo, much appreciated

VIP Super Bronze

What is the voip-null0 interface?

David,

Null0 interface is the graveyard for any packet sent to it. It is a virtual interface and it is where all packets sent to it  meets a horrible death! . Any traffic sent to this interface never comes back alive..To understand it better you can refer to this doc and thread

https://supportforums.cisco.com/docs/DOC-5714

https://learningnetwork.cisco.com/thread/3985

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Community Member

What is the voip-null0 interface?

Thanks for the comments Aokanlawon,

I understand the concept of a standard Null 0 interface, but my question was referring to the voip-null0 interface which i couldn't see the point of .  I have however had a read of the links you posted and gave myself a little refresher so that was nice

Now I know the voip-null0 interface is cosmetic I am going to remove it as a monitored interface within WhatsUp Gold.  However I still don't know how it failed to respond to icmp ping if it's logical and the router and all other interfaces remained up!

As I understand it this is a one off

Thanks again,

David

Community Member

What is the voip-null0 interface?

Most likely it wasn't an ICMP-ping issue but SNMP-get issue ) I mean that your monitoring system probably collects the snmp-status of your gateway and reacts on the loss of the voip-null0 interface (due to CEF off/on for example) like you've mentioned.

Kind regards,
Andrew C.

Kind regards, Andrew C.
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