NHRP Fields

[parthrawat979]

Can anyone help me with those different fields in NHRP especially some of them doesn't make sense to me atleast yet. The only few important one regarding DMVPN are the Fixed Header, Mandatory, Responder Address which I got to know and in those also the Client Information Entry is the only one which lifts the heavy weight. I think for DMVPN these are the only field which are necessary. Any thoughts about those fields?? And even in the CIE there are multiple fields which makes me fuzzy because I'ven't seen a lot of those field got changed or something like the MTU field haunts me, code is success for both req, and reply, the unused field etc....

[M02@rt37]

Hello @parthrawat979

Fixed header tells you the NHRP message type (registration, resolution, reply...), while the Client information entry (CIE) does the heavy lifting by mapping the tunnel IP to the NBMA/public IP, which is essentially what show dmvpn display.

Inside the CIE, Client Protocol Address, Client NBMA Address, and Holding Time are the important fields. MTU, Unused, address type/length, and even Code: Success in requests are mostly protocol legacy from NHRP’s original ATM/NBMA design and rarely change or matter in dmvpn troubleshooting...

Extensions like Responder adress help identify who reply, and cisco NAT extension become important only when spokes sit behind NAT !!!

Most of the remaining fields are inherited protocol baggage...