When an upstream LSR is overloaded for a FEC type, it notifies one or more downstream peer LSRs that it is overloaded for the FEC type.
When a downstream LSR receives overload status ON notification from an upstream LSR, it does not send further label mappings for the specified FEC type. When a downstream LSR receives overload OFF notification from an upstream LSR, it sends pending label mappings to the upstream LSR for the specified FEC type.
This feature introduces a new TLV referred to as LSR Overload Status TLV, shown below. This TLV is encoded using vendor proprietary TLV encoding as per RFC 5036. It uses a TLV type value of 0x3E02 and the Timetra OUI value of 0003FA.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Overload Status TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timetra OUI = 0003FA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
where:
U-bit: Unknown TLV bit, as described in RFC 5036. The value MUST
be 1 which means if unknown to receiver then receiver should ignore
F-bit: Forward unknown TLV bit, as described in RFC RFC5036. The value
of this bit MUST be 1 since a LSR overload TLV is sent only between
two immediate LDP peers, which are not forwarded.
S-bit: The State Bit. It indicates whether the sender is setting the
LSR Overload Status ON or OFF. The State Bit value is used as
follows:
1 - The TLV is indicating LSR overload status as ON.
0 - The TLV is indicating LSR overload status as OFF.
When a LSR that implements the procedures defined in this document generates LSR overload status, it must send LSR Overload Status TLV in a LDP Notification Message accompanied by a FEC TLV. The FEC TLV must contain one Typed Wildcard FEC TLV that specifies the FEC type to which the overload status notification applies.
The feature in this document re-uses the Typed Wildcard FEC Element which is defined in RFC 5918.