When ar$op.version == 1, the NHRP packet type is listed below.
Use of NHRP packet Types in the range 128 to 255 are reserved for
research or use in other protocol development and will be administered
by IANA as described in Section 9 of [RFC2332].
The NHRP extension Type space is subdivided to encourage use outside
the IETF.
0x0000 - 0x0FFF Reserved for NHRP.
0x1000 - 0x11FF Allocated to the ATM Forum.
0x1200 - 0x37FF Reserved for the IETF.
0x3800 - 0x3FFF Experimental use.
IANA will administer the ranges reserved for the IETF as described in
Section 9. Values in the 'Experimental use' range have only local
significance.