6. LDP Extensions for Diff-Serv Support
The MPLS architecture does not assume a single label distribution protocol. [LDP] defines the Label Distribution Protocol and its usage for establishment of label switched paths (LSPs) in MPLS networks. This section specifies the extensions to LDP to establish LSPs supporting Differentiated Services in MPLS networks.
One new LDP TLV is defined in this document:
- the Diff-Serv TLV
Detailed description of this TLV is provided below.
The new Diff-Serv TLV is optional with respect to LDP. A Diff-Serv capable LSR supporting E-LSPs which uses the Preconfigured EXP<-->PHB mapping' in compliance with this specification MAY support the Diff-Serv TLV. A Diff-Serv capable LSR supporting E-LSPs which uses the signaled EXP<-->PHB mapping' in compliance with this specification MUST support the Diff-Serv TLV. A Diff-Serv capable LSR supporting L-LSPs in compliance with this specification MUST support the Diff-Serv TLV.
6.1. Diff-Serv TLV
The Diff-Serv TLV has the following formats:
Diff-Serv TLV for an E-LSP:
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| Diff-Serv (0x0901) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved | MAPnb |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAP (MAPnb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
T (1 bit): LSP Type. This is set to 0 for an E-LSP
-
Reserved (27 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
-
MAPnb (4 bits): Indicates the number of MAP entries included in the DIFFSERV Object. This can be set to any value from 1 to 8.
-
MAP (32 bits): Each MAP entry defines the mapping between one EXP field value and one PHB. The MAP entry has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | EXP | PHBID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
Reserved (13 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
-
EXP (3 bits): This field contains the value of the EXP field for the `EXP<-->PHB mapping' defined in this MAP entry.
-
PHBID (16 bits): This field contains the PHBID of the PHB for the `EXP<-->PHB mapping' defined in this MAP entry. The PHBID is encoded as specified in [PHBID].
Diff-Serv TLV for an L-LSP:
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| Type = PSC (0x0901) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved | PSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
T (1 bit): LSP Type. This is set to 1 for an L-LSP
-
Reserved (15 bits): This field is reserved. It must be set to zero on transmission and must be ignored on receipt.
-
PSC (16 bits): The PSC indicates a PHB Scheduling Class to be supported by the LSP. The PSC is encoded as specified in [PHBID].
6.2. Diff-Serv Status Code Values
The following values are defined for the Status Code field of the Status TLV:
Status Code E Status Data
Unexpected Diff-Serv TLV 0 0x01000001
Unsupported PHB 0 0x01000002
Invalid `EXP<-->PHB mapping' 0 0x01000003
Unsupported PSC 0 0x01000004
Per-LSP context allocation failure 0 0x01000005
6.3. Diff-Serv Related LDP Messages
6.3.1. Label Request Message
The format of the Label Request message is extended as follows, to optionally include the Diff-Serv TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.2. Label Mapping Message
The format of the Label Mapping message is extended as follows, to optionally include the Diff-Serv TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.3. Label Release Message
The format of the Label Release message is extended as follows, to optionally include the Status TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.3.4. Notification Message
The format of the Notification message is extended as follows, to optionally include the Diff-Serv TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diff-Serv TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.4. Handling of the Diff-Serv TLV
6.4.1. Handling of the Diff-Serv TLV in Downstream Unsolicited Mode
This section describes operations when the Downstream Unsolicited Mode is used.
When allocating a label for an E-LSP which is to use the preconfigured `EXP<-->PHB mapping', a downstream Diff-Serv LSR issues a Label Mapping message without the Diff-Serv TLV.
When allocating a label for an E-LSP which is to use a signaled `EXP<-->PHB mapping', a downstream Diff-Serv LSR issues a Label Mapping message with the Diff-Serv TLV for an E-LSP which contains one MAP entry for each EXP value to be supported on this E-LSP.
When allocating a label for an L-LSP, a downstream Diff-Serv LSR issues a Label Mapping message with the Diff-Serv TLV for an L-LSP which contains the PHB Scheduling Class (PSC) to be supported on this L-LSP.
Assuming the label set-up is successful, the downstream and upstream LSRs must:
-
update the Diff-Serv Context associated with the established LSPs in their ILM/FTN as specified in previous sections (incoming and outgoing label),
-
install the required Diff-Serv forwarding treatment (scheduling and dropping behavior) for this NHLFE (outgoing label).
An upstream Diff-Serv LSR receiving a Label Mapping message with multiple Diff-Serv TLVs only considers the first one as meaningful. The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).
An upstream Diff-Serv LSR which receives a Label Mapping message, with the Diff-Serv TLV for an E-LSP and does not support the particular PHB encoded in one or more of the MAP entries, must reject the mapping by sending a Label Release message which includes the Label TLV and the Status TLV with a Status Code of `Unsupported PHB'.
An upstream Diff-Serv LSR receiving a Label Mapping message with the Diff-Serv TLV for an E-LSP and determining that the signaled EXP<-->PHB mapping' is invalid, must reject the mapping by sending a Label Release message which includes the Label TLV and the Status TLV with a Status Code of Invalid EXP<-->PHB mapping'. The `EXP<-->PHB mapping' signaled in the DIFFSERV Object for an E-LSP is invalid when:
-
the MAPnb field is not within the range 1 to 8, or
-
a given EXP value appears in more than one MAP entry, or
-
the PHBID encoding is invalid
An upstream Diff-Serv LSR receiving a Label Mapping message with the Diff-Serv TLV for an L-LSP containing a PSC value which is not supported, must reject the mapping by sending a Label Release message which includes the Label TLV and the Status TLV with a Status Code of `Unsupported PSC'.
6.4.2. Handling of the Diff-Serv TLV in Downstream on Demand Mode
This section describes operations when the Downstream on Demand Mode is used.
When requesting a label for an E-LSP which is to use the preconfigured `EXP<-->PHB mapping', an upstream Diff-Serv LSR sends a Label Request message without the Diff-Serv TLV.
When requesting a label for an E-LSP which is to use a signaled `EXP<-->PHB mapping', an upstream Diff-Serv LSR sends a Label Request message with the Diff-Serv TLV for an E-LSP which contains one MAP entry for each EXP value to be supported on this E-LSP.
When requesting a label for an L-LSP, an upstream Diff-Serv LSR sends a Label Request message with the Diff-Serv TLV for an L-LSP which contains the PSC to be supported on this L-LSP.
A downstream Diff-Serv LSR sending a Label Mapping message in response to a Label Request message for an E-LSP or an L-LSP must not include a Diff-Serv TLV in this Label Mapping message. Assuming the label set-up is successful, the downstream and upstream LSRs must:
-
update the Diff-Serv Context associated with the established LSPs in their ILM/FTN as specified in previous sections (incoming and outgoing label),
-
install the required Diff-Serv forwarding treatment (scheduling and dropping behavior) for this NHLFE (outgoing label).
An upstream Diff-Serv LSR receiving a Label Mapping message containing a Diff-Serv TLV in response to its Label Request message, must reject the label mapping by sending a Label Release message which includes the Label TLV and the Status TLV with a Status Code of `Unexpected Diff-Serv TLV'.
A downstream Diff-Serv LSR receiving a Label Request message with multiple Diff-Serv TLVs only considers the first one as meaningful. The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).
A downstream Diff-Serv LSR which receives a Label Request message with the Diff-Serv TLV for an E-LSP and does not support the particular PHB encoded in one (or more) of the MAP entries, must reject the request by sending a Notification message which includes the Status TLV with a Status Code of `Unsupported PHB'.
A downstream Diff-Serv LSR receiving a Label Request message with the Diff-Serv TLV for an E-LSP and determining that the signaled EXP<-->PHB mapping' is invalid, must reject the request by sending a Notification message which includes the Status TLV with a Status Code of Invalid EXP<-->PHB mapping'. The `EXP<-->PHB mapping' signaled in the DIFFSERV TLV for an E-LSP is invalid when:
-
the MAPnb field is not within the range 1 to 8, or
-
a given EXP value appears in more than one MAP entry, or
-
the PHBID encoding is invalid
A downstream Diff-Serv LSR receiving a Label Request message with the Diff-Serv TLV for an L-LSP containing a PSC value which is not supported, must reject the request by sending a Notification message which includes the Status TLV with a Status Code of `Unsupported PSC'.
A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in a Label Request message but is unable to allocate the required per-LSP context information, must reject the request sending a Notification message which includes the Status TLV with a Status Code of `Per-LSP context allocation failure'.
A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in a Label Request message and supports the requested PSC but is not able to satisfy the label request for other reasons (e.g., no label available), must send a Notification message in accordance with existing LDP procedures [LDP] (e.g., with a `No Label Resource' Status Code). This Notification message must include the requested Diff-Serv TLV.
6.5. Non-Handling of the Diff-Serv TLV
An LSR that does not recognize the Diff-Serv TLV Type, on receipt of a Label Request message or a Label Mapping message containing the Diff-Serv TLV, must behave in accordance with the procedures specified in [LDP] for an unknown TLV whose U Bit and F Bit are set to 0 i.e., it must ignore the message, return a Notification message with `Unknown TLV' Status.
6.6. Bandwidth Information
Bandwidth information may also be signaled at the establishment time of E-LSP and L-LSP, for instance for the purpose of Traffic Engineering, using the Traffic Parameters TLV as described in [MPLS CR LDP].