Code,Description,Reference
0,Padding - copy in response,[RFC6374]
1,Return Address,[RFC6374]
2,Session Query Interval,[RFC6374]
3,Loopback Request,[RFC6374]
4,Synonymous Flow Label,[RFC9571]
5,Return Path,[RFC9779]
6,Block Number,[RFC9779]
7-126,Unassigned,
127,Experimental use,[RFC6374]
128,Padding - do not copy in response,[RFC6374]
129,Destination Address,[RFC6374]
130,Source Address,[RFC6374]
131,UDP Return,[RFC7876]
132-254,Unassigned,
255,Experimental use,[RFC6374]