Value,Meaning,Reference
0,No Return Code,[RFC8029]
1,Malformed echo request received,[RFC8029]
2,One or more of the TLVs was not understood,[RFC8029]
3,Replying router is an egress for the FEC at stack-depth <RSC>,[RFC8029]
4,Replying router has no mapping for the FEC at stack-depth <RSC>,[RFC8029]
5,Downstream Mapping Mismatch (See [1]),[RFC8029]
6,Upstream Interface Index Unknown (See [1]),[RFC8029]
7,Reserved,[RFC8029]
8,Label switched at stack-depth <RSC>,[RFC8029]
9,Label switched but no MPLS forwarding at stack-depth <RSC>,[RFC8029]
10,Mapping for this FEC is not the given label at stack-depth <RSC>,[RFC8029]
11,No label entry at stack-depth <RSC>,[RFC8029]
12,Protocol not associated with interface at FEC stack-depth <RSC>,[RFC8029]
13,"Premature termination of ping due to label stack             
shrinking to a single label",[RFC8029]
14,See DDMAP TLV for meaning of Return Code and Return Subcode (See [2]),[RFC8029]
15,Label switched with FEC change,[RFC8029]
16,Proxy Ping not authorized,[RFC7555]
17,Proxy Ping parameters need to be modified,[RFC7555]
18,MPLS Echo Request could not be sent,[RFC7555]
19,Replying router has FEC mapping for topmost FEC,[RFC7555]
20,One or more TLVs not returned due to MTU size,[RFC7743]
21,OAM Problem/Unsupported BFD Version,[RFC7759]
22,OAM Problem/Unsupported BFD Encapsulation format,[RFC7759]
23,OAM Problem/Unsupported BFD Authentication Type,[RFC7759]
24,OAM Problem/Mismatch of BFD Authentication Key ID,[RFC7759]
25,OAM Problem/Unsupported Timestamp Format,[RFC7759]
26,OAM Problem/Unsupported Delay Mode,[RFC7759]
27,OAM Problem/Unsupported Loss Mode,[RFC7759]
28,OAM Problem/Delay variation unsupported,[RFC7759]
29,OAM Problem/Dyadic mode unsupported,[RFC7759]
30,OAM Problem/Loopback mode unsupported,[RFC7759]
31,OAM Problem/Combined mode unsupported,[RFC7759]
32,OAM Problem/Fault management signaling unsupported,[RFC7759]
33,OAM Problem/Unable to create fault management association,[RFC7759]
34,OAM Problem/PM Configuration Error,[RFC7759]
35,Mapping for this FEC is not associated with the incoming interface,"[RFC8287, Section 7.4]"
36,"Replying router is an egress for the address in the Egress TLV for the FEC at
        stack depth <RSC>",[RFC9655]
37,"Replying router is egress for the FEC at the stack depth. In addition, the BUM packets are dropped on the ES corresponding to the ESI received in EVPN Ethernet Auto-Discovery sub-TLV because of the Split Horizon Group filtering.",[RFC9489]
38,"Replying router is egress for the FEC at the stack depth. In addition, the BUM packets are forwarded because there is no ES corresponding to the ESI received in EVPN Ethernet Auto-Discovery sub-TLV.",[RFC9489]
39-191,Unassigned,
192,Inappropriate Target FEC Stack sub-TLV present,[RFC9612]
193,Failed to establish the BFD session. The specified reverse path was not found.,[RFC9612]
194-247,Unassigned,
248-251,Reserved for Experimental Use,[RFC9041]
252-255,Reserved for Private Use,[RFC8029]