04-13-2007 11:38 PM - edited 03-03-2019 04:32 PM
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.
04-14-2007 02:57 AM
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!
04-14-2007 03:38 PM
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.
04-15-2007 01:34 PM
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
04-15-2007 02:24 PM
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.
04-15-2007 04:12 PM
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
04-16-2007 01:18 AM
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
04-16-2007 02:38 AM
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.
04-16-2007 03:06 AM
Even i didn't knew about it
Rick deserves a rating.
Narayan
04-16-2007 06:30 AM
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,
04-16-2007 06:47 AM
Thanks harold.
Ya i got to know that only when tried configuring it
Narayan
04-16-2007 06:34 AM
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,
05-30-2018 04:46 AM
just as an addon:
Works fine with
a) static-GRE-Tunnels
b) dynamic-GRE-Tunnels(FlexVPN) - even FlexVPN Site-to-Site Shortcuts!
RTR-95#show cdp neigh Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone, D - Remote, C - CVTA, M - Two-port Mac Relay Device ID Local Intrfce Holdtme Capability Platform Port ID RTR-11 Tunnel4011 154 R I ASR1009-X Virtual-Access3 ***FlexVPN Spoke-to-Hub*** RTR-91 Gig 0/0/0 179 R I ASR1002-H Gig 0/0/1 RTR-17 Virtual-Access1 176 R S I ISR4221/K Virtual-Access1 ***Shortcut: Spoke-to-Spoke***
06-10-2021 06:33 PM
Alright,
I have two ISR's connected over GRE, and in fact CDP is working over them. But the new CSR's are
not passing GRE over wan links(yes I have CDP enabled on the interfaces), and wondered if anyone had insight, as Network Assistant will not work without it.
Attached is my show cdp neighbor statement from NCToSC... but I have three cloud routers and they arent working... perhaps because the Virtual Networks are abstracted from the Core Networks which dont have
CDP enabled... but it should work inside a tunnel interface anyway.
Thanks,
SF
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