Value,Meaning,Reference
0,Reserved,[RFC9041]
1,Do not reply,[RFC8029]
2,Reply via an IPv4/IPv6 UDP packet,[RFC8029]
3,Reply via an IPv4/IPv6 UDP packet with Router Alert (DEPRECATED),[RFC8029][RFC9570]
4,Reply via application-level control channel,[RFC8029]
5,Reply via Specified Path,[RFC7110]
6-247,Unassigned,
248-251,Reserved for Experimental Use,[RFC9041]
252-255,Reserved for Private Use,[RFC8029]