Are you talking about this command?
ip nhrp network-id 100001
Not sure what you found, but everyone of our sites has the same network-id, and we have over 100 sites and have not had any issues.
Found this:
http://www.cisco.com/en/US/tech/tk583/tk372/technologies_white_paper09186a008018983e.shtml
The ip nhrp authentication ..., ip nhrp network-id ... and tunnel key ... commands are used to map the tunnel packets and the NHRP packets to the correct multipoint GRE tunnel interface and NHRP network when they are received on the hub.
Alos this:
http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_nhrp.html#wp1011629
ip nhrp network-id
To enable the Next Hop Resolution Protocol (NHRP) on an interface, use the ip nhrp network-id command in interface configuration mode. To disable NHRP on the interface, use the no form of this command.
ip nhrp network-id number
no ip nhrp network-id [number]
Syntax Description
number
Globally unique, 32-bit network identifier from a nonbroadcast multiaccess (NBMA) network. The range is from 1 to 4294967295.
Defaults
NHRP is disabled on the interface.
Command Modes
Interface configuration
Command History
Release Modification
10.3
This command was introduced.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Usage Guidelines
In general, all NHRP stations within one logical NBMA network must be configured with the same network identifier.
Notice the last part.
Kind of like BGP or EIGRP, if you create this you will need to make sure that all networks that connect together and need to talk will have the same network-id number.
