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Enabling cdp on GRE tunnel..

Hi,

I am issuing the command "cdp enable" on tunnel interface of routers. On some of the routers its accepting the command and I can see it in the "sh run" but on some of the routers its giving the error "% CDP is not supported on this interface, or for this encapsulation". I have checked the encapsulation on every gre tunnel interface and its "tunnel" no matter cdp can be enabled or no. Pls help me to know why am I getting this error. Thanks.

11 REPLIES
Hall of Fame Super Gold

Re: Enabling cdp on GRE tunnel..

Sorry, you can't have CDP on GRE.

CDP is not IP hence cannot be carried by GRE.

Hope this helps, if so please rate post!

Hall of Fame Super Bronze

Re: Enabling cdp on GRE tunnel..

CDP only runs over Layer2 interfaces, in other words, physical interfaces.

A GRE tunnel is a logical interface hence the lack of support for this feature/service.

Bronze

Re: Enabling cdp on GRE tunnel..

Hi

i agree with your point, i have check up in 7200 serial router , in tunnel configuration, cdp enable is there , but unfortunely my envirement is live , so i could not try too much , but atleast i can say in 7200 series router, this feature is available, may be other router do not have this feature.

i hope this will help , please rate this post.

-Minu

Hall of Fame Super Gold

Re: Enabling cdp on GRE tunnel..

The fact that you can configure cdp under a tunnel interface does not mean it will work, for the reasons explained above.

In IOS there are many commands that are configurable, but without effect and no warning is given.

Hall of Fame Super Silver

Re: Enabling cdp on GRE tunnel..

Paolo

Your logic sounds convincing and used to be true but is in fact not correct any longer. It is a release dependent behavior. I have a lot of routers running 12.3T code and 12.4 code that are successfully running CDP over GRE tunnels. I am confident that if Syed will look at the routers where it works (is accepted) and the ones where it does not work (is not accepted) that he will find differences in the versions of code.

I speak from direct personal experience when I say that in at least some versions of code that CDP does work over GRE tunnels.

HTH

Rick

Re: Enabling cdp on GRE tunnel..

Rick is right.

I did a quick test to find this out.

The CDP does not show any information when i run a GRE tunnel between a ISR and a 2621XM router. There is no support for the smae

MS_VTR_PUN_R01(config)#int tunnel 3

MS_VTR_PUN_R01(config-if)#cd

MS_VTR_PUN_R01(config-if)#cdp en

MS_VTR_PUN_R01(config-if)#cdp enable

% CDP is not supported on this interface, or for this encapsulation

But when i tried the same between 2 ISR 2811 routers it does work

MS_M6_MPLS_TATA#sh cdp neighbors

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater

Device ID Local Intrfce Holdtme Capability Platform Port ID

M5 Tunnel0 176 R S I 2811 Tunnel0

Interface are shown as tunnel 0

Narayan

Please rate useful posts

Hall of Fame Super Gold

Re: Enabling cdp on GRE tunnel..

Good to know, so it appears this feature has been added at some point in IOS. Certainly it does not depend by the hardware.

Thanks to those that have pointed out and tried.

Re: Enabling cdp on GRE tunnel..

Even i didn't knew about it

Rick deserves a rating.

Narayan

Cisco Employee

Re: Enabling cdp on GRE tunnel..

CDP support on GRE tunnel interfaces was integrated in 12.3(5) and 12.3(6)T via CSCec01500.

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCec01500

Note that unlike other interfaces, CDP is not enabled by default and must be explicitly enabled on the GRE tunnel interface.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: Enabling cdp on GRE tunnel..

Thanks harold.

Ya i got to know that only when tried configuring it

Narayan

Cisco Employee

Re: Enabling cdp on GRE tunnel..

Before CSCec01500, configuring CDP on a tunnel interface would lead to the following message:

RouterC(config-if)#cdp enable

% CDP is not supported on this interface, or for this encapsulation

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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