Type,Name,Reference
0,The End of Extensions,[RFC2332]
1-2,Unassigned,
3,Responder Address Extension,[RFC2332]
4,NHRP Forward Transit NHS Record Ext.,[RFC2332]
5,NHRP Reverse Transit NHS Record Ext.,[RFC2332]
7,NHRP Authentication Extension,[RFC2332]
8,NHRP Vendor-Private Extension,[RFC2332]
9,Unassigned,
10,NHRP Mobile NHC Authentication Ext.,[RFC2520]