DMVPN -- IP NHRP SHORTCUT

Unanswered Question
Jul 16th, 2009

I am new to DMVPN but have performed extensive research to understand the ins and outs of this technology starting with phase 1, 2 and now phase 3. I have taken the time to understand the technology, each command, related syntax, design options and scalability considerations.

The command IP NHRP SHORTCUT appears in the phase-3 documentation and Cisco provides very little details on this command. Cisco has forgotten to provide real details on this option and it seems to be sort of important in spoke-to-spoke communications. Cisco's command lookup tool reveals nothing useful nor does a web search. I see IP NHRP REDIRECT is used on phase-3 HUBs -used to redirect spoke-to-spoke communication. Cisco documented this command fairly well; and these two commands always seem to appear together for phase-3.

Cisco Command tool

Usage Guidelines:

Do not configure this command if the DMVPN network is configured for full-mesh. In a full-mesh configuration the spokes are populated with a full routing table with next-hop being the other spokes.

Can anyone help?

Tks Frank

I have this problem too.
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Giuseppe Larosa Thu, 07/16/2009 - 12:23

Hello Frank,

I've found this presentations taken from a networkers session

http://www.cisco.com/en/US/prod/collateral/vpndevc/ps6525/ps9370/ps6658/prod_presentation0900aecd80313ca9.pdf

see slide 11

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6635/ps6658/prod_presentation0900aecd80313ca3.pdf

the RFC that defines NHRP is

http://www.faqs.org/rfcs/rfc2332.html

it speaks of a "short mode"

Probably it depends on scalability considerations and related choices.

it is not suggested where direct sopke to spoke tunnels should be built without going through the NHS/hub(s)

I think unless you are designing a very big DMVPN that you can use full mesh design.

Hope to help

Giuseppe

fsebera Fri, 07/17/2009 - 07:35

Thanks!!!!

I'll read through these details -

It's strange Cisco would not provide clear coverage on such an old technology.

Anyway, Thanks for assisting.

Frank

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