The procedures defined in this document apply only to LSRs that support Downstream Unsolicited (DU) label advertisement mode and Liberal Label Retention Mode. An LSR that implements the LSR overload protection follows the following procedures:
When an upstream LSR detects that it is overloaded with a FEC type then it must initiate an LDP notification message with the S-bit ON in LSR Overload Status TLV and a FEC TLV containing the Typed Wildcard FEC Element for the specified FEC type. This message may be sent to one or more peers.
After it has notified peers of its overload status ON for a FEC type, the overloaded upstream LSR can send Label Release for a set of FEC elements to respective downstream LSRs to off load its LIB to below a specified watermark.
When an upstream LSR that was previously overloaded for a FEC type detects that it is no longer overloaded, it must send an LDP notification message with the S-bit OFF in LSR Overload Status TLV and FEC TLV containing the Typed Wildcard FEC Element for the specified FEC type.
When an upstream LSR has notified its peers that it is overloaded for a FEC type, then a downstream LSR must not send new label mappings for the specified FEC type to the upstream LSR.
When a downstream LSR receives LSR overload notification from a peering LSR with status OFF for a FEC type then the receiving LSR must send any label mappings for the FEC type which were pending to the upstream LSR for which are eligible to be sent now.
When an upstream LSR is overloaded for a FEC type and it receives Label Mapping for that FEC type from a downstream LSR then it can send Label Release to the downstream peer for the received Label Mapping with LDP Status Code as No_Label_Resources as defined in RFC 5036.