BMP Extension for Path Status TLV

2.1. IANA-registered Path Status TLV

 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
+-------------------------------+-------------------------------+
|E|       Type (15 bits)        |       Length (2 octets)       |
+---------------------------------------------------------------+
|        Index (2 octets)       |
+-------------------------------+-------------------------------+
|                      Path Status (4 octets)                   |
+---------------------------------------------------------------+
|                 Reason Code (2 octets, optional)              |
+---------------------------------------------------------------+

    Figure 2: Encoding of IANA-Registered Path Status TLV

• E bit: For an IANA-registered TLV, the E bit MUST be set to 0 [I-D.ietf-grow-bmp-tlv-ebit].¶
• Type = TBD2 (15 Bits): indicates that it is the IANA-registered Path Status TLV.¶
• Length (2 Octets): indicates the length of the value field of the Path Status TLV. The value field further consists of the Path-Status field and Reason Code field.¶
• Index (2 Octets): indicates the prefix that this TLV is describing. Please see [I-D.ietf-grow-bmp-tlv] for details of the use of the index field to associate the path marking content with one or more NLRIs.¶
• Path Status (4 Octets): indicates the path status of the BGP Update PDU encapsulated in the RM Message. Currently 10 types of path status are defined, as shown in Table 1. All zeros are reserved.¶
• Reason Code (2 Octets, optional): indicates the reason of the path status indicated in the Path Status field. The reason code field is optional. If no reason code is carried, this field is empty. If a reason code is carried, the reason code is indicated by a 2-byte value, which is defined in Table 2.¶

+------------+-----------------------------+
| Value      | Path type                   |
+------------------------------------------+
| 0x00000000 | Reserved                    |
| 0x00000001 | Invalid                     |
| 0x00000002 | Best                        |
| 0x00000004 | Non-selected                |
| 0x00000008 | Primary                     |
| 0x00000010 | Backup                      |
| 0x00000020 | Non-installed               |
| 0x00000040 | Best-external               |
| 0x00000080 | Add-Path                    |
| 0x00000100 | Filtered in inbound policy  |
| 0x00000200 | Filtered in outbound policy |
| 0x00000400 | Invalid ROV                 |
+------------+-----------------------------+

Table 1: IANA-Registered Path Type

The Path Status field contains a bitmap where each bit encodes a specific role of the path. Multiple bits may be set when multiple path status apply to a path.¶

• The best-path is defined in RFC4271 [RFC4271] and the best-external path is defined in draft-ietf-idr-best-external [I-D.ietf-idr-best-external].¶
• An invalid path is a route that does not enter the BGP decision process.¶
• A non-selected path is a route that is not selected in the BGP decision process. Back-up routes are considered non-selected, while the best and ECMP routes are not considered as non-selected.¶
• A primary path is a recursive or non-recursive path whose nexthop resolution ends with an adjacency draft-ietf-rtgwg-bgp-pic [I-D.ietf-rtgwg-bgp-pic]. A prefix can have more than one primary path if multipath is configured draft-lapukhov-bgp-ecmp-considerations [I-D.lapukhov-bgp-ecmp-considerations]. A best-path is also considered as a primary path.¶
• A backup path is also installed in the RIB, but it is not used until some or all primary paths become unreachable. Backup paths are used for fast convergence in the event of failures.¶
• A non-installed path refers to the route that is not installed into the IP routing table.¶
• For the advertisement of multiple paths for the same address prefix without the new paths implicitly replacing any previous ones, the add-path status is applied [RFC7911].¶

The path status TLV does not force a BMP client to send any of these paths. It just provides a method to mark the paths that are available with their status.¶

+----------+-----------------------------------------------------+
|   Value  | Reason code                                         |
+----------------------------------------------------------------+
| [0x0007] | invalid for AS loop                                 |
| [0x0007] | invalid for unresolvable nexthop                    |
| [0x0016] | not preferred for Local preference                  |
| [0x0014] | not preferred for AS Path Length                    |
| [0x0013] | not preferred for origin                            |
| [0x0012] | not preferred for MED                               |
| [0x0011] | not preferred for peer type                         |
| [0x0010] | not preferred for IGP cost                          |
| [0x000E] | not preferred for router ID                         |
| [0x000D] | not preferred for peer address                      |
| [0x0020] | not preferred for AIGP                              |
+----------+-----------------------------------------------------+

               Table 2: IANA-Registered Reason Code

2.2. Enterprise-specific Path Status TLV

 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
+-------------------------------+-------------------------------+
|E|       Type (15 bits)        |       Length (2 octets)       |
+-------------------------------+-------------------------------+
|                      PEN number (4 octets)                    |
+---------------------------------------------------------------+
|        Index (2 octets)       |
+---------------------------------------------------------------+
|                      Path Status (4 octets)                   |
+---------------------------------------------------------------+
|               Reason Code (2 octets, optional)                |
+---------------------------------------------------------------+

   Figure 3: Encoding of Enterprise-specific Path Status TLV

• E bit: For an Enterprise-specific TLV, the E bit MUST be set to 1 [I-D.ietf-grow-bmp-tlv-ebit].¶
• Type = 1 (15 Bits): indicates that it's the Enterprise-specific Path Status TLV.¶
• Length (2 Octets): indicates the length of the value field of the Path Status TLV. The value field further consists of the Path-Status field and Reason Code field.¶
• Index (2 Octets): indicates the prefix that this TLV is describing. The index is the encapsulation order, starting from 0, of the prefix in the BGP Update PDU.¶
• PEN Number (4 octets): indicates the IANA enterprise number IANA-PEN.¶
• Path Status (4 Octets): indicates the enterprise-specific path status. The format is to be determined w.r.t. each PEN number.¶
• Reason Code (2 octets, optional): indicates the reasons/explanations of the path status indicated in the Path Status field. The format is to be determined w.r.t. each PEN number.¶