SRv6 Path Egress Protection

3.1. Mechanism

Figure 1 is used to explain the mechanism of SR path egress node protection.¶

            *******  *******   SIDa
        [PE1]-----[P1]-----[PEA]---[CE2]    PEA Egress
        / |        |&        | \   /        PEB Backup Egress
       /  |        |&        |  \ /         CEx Customer Edge
  [CE1]   |        |&        |   X          Px  Non-Provider Edge
       \  |        |&        |  / \         *** SR Path
        \ |        |& &&&&&  | /   \        &&& Backup Path
        [PE2]-----[P2]-----[PEB]---[CE3]
                        Mirror SID

Where node PEA is the egress of the SR path from PE1 to PEA, and has SIDa which is the active segment in the packet from the SR path at PEA. Node PEB is the backup egress (or say protector) to provide the protection for egress (or say primary egress) PEA. Node P1 is the direct previous hop of egress PEA and acts as PLR to support the protection for PEA.¶

When PEB is selected as a backup egress to protect the egress PEA, a Mirror SID (refer to Section 5.1 of [RFC8402]) is configured on PEB to protect PEA. PEB advertises this information through IGP, which includes the Mirror SID and the egress PEA. The information is represented by <PEB, PEA, Mirror SID>, which indicates that PEB protects PEA with Mirror SID.¶

After PEA receives the information <PEB, PEA, Mirror SID>, it may send the forwarding behavior of the SIDa at PEA to PEB with the Mirror SID using some protocols such as BGP if PEB can not obtain this behavior from other approaches if PEB wants to protect SIDa of PEA. How to send the forwarding behavior of the SIDa to PEB is out scope of this document.¶

When PEB gets the forwarding behavior of the SIDa of PEA from PEA or other means, it adds a forwarding entry for the SIDa according to the behavior into the forwarding table for node PEA. This table is identified by the Mirror SID, which indicates node PEA's context. Using the forwarding entry for SIDa in this table, a packet with SIDa will be transmitted by PEB to the same destination as it is transmitted by PEA. For example, assume that the packet with SIDa is transmitted by PEA to CE2 through the forwarding behavior of the SIDa in PEA. The packet will be transmitted by PEB to the same CE2 through looking up the table identified by the Mirror SID.¶

After P1 as PLR receives the information <PEB, PEA, Mirror SID> and knows that PEB wants to protect SIDa of PEA, it computes a shortest path to PEB. A Repair List RL is obtained based on the path. It is one of the followings:¶

o

RL = <Mirror SID> if the path does not go through PEA; or¶

o

RL = <S1, ..., Sn, Mirror SID> if the path goes through PEA, where <S1, ..., Sn> is the TI-LFA Repair List to PEB computed by P1.¶

When PEA fails, P1 as PLR sends the packet with SIDa carried by the SR path to PEB, but encapsulates the packet before sending it by executing H.Encaps with the Repair List RL and a Source Address T.¶

Suppose that the packet received by P1 is represented by Pkt = (S, SIDa)Pkt0, where SA = S and DA = SIDa, and Pkt0 is the rest of the packet.¶

The execution of H.Encaps pushes an IPv6 header to Pkt and sets some fields in the outer and inner IPv6 header to produce an encapsulated packet Pkt'. Pkt' will be one of the followings:¶

o

Pkt' = (T, Mirror SID) (S, SIDa)Pkt0 if RL = <Mirror SID>; or¶

o

Pkt' = (T, S1)(Mirror SID, Sn, ..., S1; SL=n) (S, SIDa)Pkt0 if RL = <S1, ..., Sn, Mirror SID>.¶

When PEB receives the re-routed packet, which is (T, Mirror SID) (S, SIDa)Pkt0, it decapsulates the packet and forwards the decapsulated packet using the FIB table Tm identified by the Mirror SID as a variant of End.DT6 SID. The Mirror SID is called End.M.¶

It obtains the Mirror SID in the outer IPv6 header of the packet, removes this outer IPv6 header with all its extension headers, and then processes the inner IPv6 packet (i.e., (S, SIDa)Pkt0, the packet without the outer IPv6 header). PEB finds the FIB table Tm for node PEA using the Mirror SID as the context ID, and submits the packet to this FIB table lookup and transmission to the same destination as PEA does.¶

The behavior of Mirror SID (End.M for short) is a variant of the End.DT6 behavior (refer to Section 4.6 of [RFC8986]). The End.M SID MUST be the last segment in an SR path, and a SID instance is associated with an IPv6 FIB table Tm.¶

When processing the Upper-Layer header of a packet matching a FIB entry locally instantiated as an End.M SID, N does the following:¶

    S01. If (Upper-Layer header type == 41(IPv6) ) {
    S02.    Remove the outer IPv6 header with all its extension headers
    S03.    Set the packet's associated FIB table to Tm
    S04.    Submit the packet to the egress IPv6 FIB lookup for
               transmission to the new destination
    S05. } Else {
    S06.    Process as per Section 4.1.1 of RFC8986
    S07. }

3.2. Example

Figure 2 shows an example of protecting egress PE3 of a SR path, which is from ingress PE1 to egress PE3.¶

                                Locator: A3:1::/64
              *******  *******  VPN SID: A3:1::B100
          [PE1]-----[P1]-----[PE3]---[CE2]      PE3 Egress
          / |        |&        | \   /          PE4 Backup Egress
         /  |        |&        |  \ /           CEx Customer Edge
    [CE1]   |        |&        |   X            Px  Non-Provider Edge
         \  |        |&        |  / \           *** SR Path
          \ |        |& &&&&&  | /   \          &&& Backup Path
          [PE2]-----[P2]-----[PE4]---[CE3]
                                Locator: A4:1::/64
                                VPN SID: A4:1::B100
                             Mirror SID: A4:1::3, protect A3:1::/64

Where node P1's pre-computed backup path for PE3 is from P1 to PE4 via P2. In normal operations, after receiving a packet with destination PE3, P1 forwards the packet to PE3 according to its FIB. When PE3 receives the packet, it sends the packet to CE2.¶

When PE3 fails, P1 as PLR detects the failure through using a failure detection mechanism such as BFD and forwards the packet to PE4 via the backup path. When PE4 receives the packet, it sends the packet to the same CE2.¶

In Figure 2, Both CE2 and CE3 are dual home to PE3 and PE4. PE3 has a locator A3:1::/64 and a VPN SID A3:1::B100. PE4 has a locator A4:1::/64 and VPN SID A4:1::B100. A Mirror SID A4:1::3 is configured on PE4 for protecting PE3 with locator A3:1::/64.¶

After the configuration, PE4 advertises this information through an IGP LS (i.e., LSA in OSPF or LSP in IS-IS), which includes PE3's locator and Mirror SID A4:1::3. Every node in the SR domain will receive this IGP LS, which indicates that PE4 wants to protect PE3's locator with Mirror SID A4:1::3.¶

When PE4 (e.g., BGP on PE4) receives a prefix whose VPN SID belongs to PE3 that is protected by PE4 through Mirror SID A4:1::3, it finds PE4's VPN SID corresponding to PE3's VPN SID. For example, local PE4 has Prefix 1.1.1.1 with VPN SID A4:1::B100, when PE4 receives prefix 1.1.1.1 with remote PE3's VPN SID A3:1::B100, it knows that they are for the same VPN.¶

The forwarding behaviors for these two VPN SIDs are the same from function's point of view. If the behavior for PE3's VPN SID in PE3 forwards the packet with it to CE2, then the behavior for PE4's VPN SID in PE4 forwards the packet to the same CE2; and vice versa. PE4 creates a forwarding entry for PE3's VPN SID A3:1::B100 in the FIB table identified by Mirror SID A4:1::3 according to the forwarding behavior for PE4's VPN SID A4:1::B100.¶

Node P1's pre-computed backup path for destination PE3`s locator is from P1 to PE4 having mirror SID A4:1::3. When P1 receives a packet destined to PE3's VPN SID A3:1::B100, in normal operations, it forwards the packet with source A1:1:: and destination PE3's VPN SID A3:1::B100 according to the FIB using the destination PE3's VPN SID A3:1::B100.¶

When PE3 fails, P1 as PLR sends the packet to PE4 via the backup path pre-computed. P1 encapsulates the packet using H.Encaps before sending it to PE4.¶

Suppose that the packet received by P1 is represented by Pkt = (SA = A1:1::, DA = A3:1::B100)Pkt0, where DA = A3:1::B100 is PE3's VPN SID, and Pkt0 is the rest of the packet. The encapsulated packet Pkt' will be one of the followings:¶

o

Pkt' = (T, Mirror SID A4:1::3) (A1:1::, A3:1::B100)Pkt0 if backup path not via PE3; or (otherwise)¶

o

Pkt' = (T, S1)(Mirror SID A4:1::3, Sn, ..., S1; SL=n) (A1:1::, A3:1::B100)Pkt0.¶

where T is a Source Address, <S1, ..., Sn> is the TI-LFA Repair List to PE4 computed by P1 when the backup path to PE4 goes through PE3.¶

When PE4 receives the re-routed packet, it decapsulates the packet and forwards the decapsulated packet by executing End.DT6 behavior for an End.DT6 SID instance. The SID instance is End.M, the Mirror SID that is associated with the IPv6 FIB table for PE3. The packet received by PE4 is (T, Mirror SID A4:1::3) (A1:1::, PE3's VPN SID A3:1::B100)Pkt0.¶

PE4 obtains Mirror SID A4:1::3 in the outer IPv6 header of the packet, removes this outer IPv6 header, and then processes the inner IPv6 packet (A1:1::, A3:1::B100)Pkt0. It finds the FIB table for PE3 using Mirror SID A4:1::3 as the context ID, gets the forwarding entry for PE3's VPN SID A3:1::B100 from the table, and forwards the packet to CE2 using the entry.¶

4.1. Extensions to IS-IS

A new sub-TLV, called IS-IS SRv6 Mirror SID sub-TLV, is defined. It is used in the SRv6 Locator TLV defined in [I-D.ietf-lsr-isis-srv6-extensions] to advertise SRv6 Mirror SID and the locators of the node to be protected. The SRv6 Mirror SID inherit the topology/algorithm from the parent locator. The format of the sub-TLV is illustrated below.¶

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Type (TBD1)   |    Length     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Flags     |    SRv6 Endpoint Function     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         SID (16 octets)                       |
 :                                                               :
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            sub-TLVs                           |
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD1 (suggested value 8) is to be assigned by IANA.¶

Length:

variable.¶

Flags:

1 octet. No flags are currently defined.¶

SRv6 Endpoint Function:

2 octets. It contains the endpoint function 74 for Mirror SID.¶

SID:

16 octets. This field contains the SRv6 Mirror SID to be advertised.¶

Two sub-TLVs are defined. One is the protected locators sub-TLV, and the other is the protected SIDs sub-TLV.¶

A protected locators sub-TLV is used to carry the Locators to be protected by the SRv6 mirror SID. It 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Type (TBD2)  |    Length     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Locator-Size  | Locator (variable)            ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Locator-Size  | Locator (variable)            ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD2 (suggested value 1) is to be assigned by IANA.¶

Length:

variable.¶

Locator-Size:

1 octet. Number of bits (1 - 128) in the Locator field.¶

Locator:

1-16 octets. This field encodes an SRv6 Locator to be protected by the SRv6 mirror SID. The Locator is encoded in the minimal number of octets for the given number of bits.¶

A protected SIDs sub-TLV is used to carry the SIDs to be protected by the SRv6 Mirror SID. It 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Type (TBD3)  |    Length     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   SID-Size    |         SID (variable)                        ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   SID-Size    |         SID (variable)                        ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD3 (suggested value 2) is to be assigned by IANA.¶

Length:

variable.¶

SID-Size:

1 octet. Number of bits in the SID field. It is from 1 to 128. When it is less than 128, the SID field is a locator. When it is 128, the SID field is an SRv6 SID.¶

SID:

1-16 octets. This field encodes an SRv6 SID or locator to be protected. The SID/locator is encoded in the minimal number of octets for the given number of bits. Trailing bits MUST be set to zero and ignored when received.¶

When node B advertises that B wants to protect node A's locators with a Mirror SID through an LSP, the LSP contains an IS-IS SRv6 Mirror SID sub-TLV, which includes the Mirror SID and the node A's locators in an IS-IS Protected locators sub-TLV. If B wants to protect just a specific set of SIDs of node A, the Mirror SID sub-TLV includes these SIDs in an IS-IS Protected SIDs sub-TLV.¶

4.2. Extensions to OSPF

Similarly, a new sub-TLV, called OSPF Mirror SID sub-TLV, is defined. It is used to advertise SRv6 Mirror SID and the locators of the node to be protected. Its format is illustrated below.¶

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Type (TBD4)           |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Flags     |    SRv6 Endpoint Function     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         SID (16 octets)                       |
 :                                                               :
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            sub-TLVs                           |
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD4 (suggested value 8) is to be assigned by IANA.¶

Length:

variable.¶

Flags:

1 octet. No flags are currently defined.¶

SRv6 Endpoint Function:

2 octets. It contains the endpoint function 74 for End.M SID.¶

SID:

16 octets. This field contains the SRv6 Mirror SID to be advertised.¶

Two sub-TLVs are defined. One is the protected locators sub-TLV, and the other is the protected SIDs sub-TLV.¶

A protected locators sub-TLV is used to carry the locators of the node to be protected by the SRv6 Mirror SID. It 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Type (TBD5)           |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Locator-Size  |  Locator (variable)           ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Locator-Size  |  Locator (variable)           ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD5 (suggested value 1) is to be assigned by IANA.¶

Length:

variable.¶

Locator-Size:

1 octet. Number of bits (1 - 128) in the Locator field.¶

Locator:

1-16 octets. This field encodes an SRv6 Locator to be protected by the SRv6 mirror SID. The Locator is encoded in the minimal number of octets for the given number of bits.¶

A protected SIDs sub-TLV is used to carry the SIDs to be protected by the SRv6 Mirror SID. It 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Type (TBD6)           |             Length            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   SID-Size    |         SID (variable)                        ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :                                                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   SID-Size    |         SID (variable)                        ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBD6 (suggested value 2) is to be assigned by IANA.¶

Length:

variable.¶

SID-Size:

1 octet. Number of bits in the SID field. It is from 1 to 128. When it is less than 128, the SID field is a locator. When it is 128, the SID field is an SRv6 SID.¶

SID:

1-16 octets. This field encodes an SRv6 SID or locator to be protected. The SID/locator is encoded in the minimal number of octets for the given number of bits. Trailing bits MUST be set to zero and ignored when received.¶

8.1. Normative References

[I-D.ietf-lsr-isis-srv6-extensions]

Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extensions to Support Segment Routing over IPv6 Dataplane", Work in Progress, Internet-Draft, draft-ietf-lsr-isis-srv6-extensions-17, 18 June 2021, <https://www.ietf.org/archive/id/draft-ietf-lsr-isis-srv6-extensions-17.txt>.

[I-D.ietf-lsr-ospfv3-srv6-extensions]

Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, "OSPFv3 Extensions for SRv6", Work in Progress, Internet-Draft, draft-ietf-lsr-ospfv3-srv6-extensions-02, 15 February 2021, <https://www.ietf.org/archive/id/draft-ietf-lsr-ospfv3-srv6-extensions-02.txt>.

[RFC2119]

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.

[RFC7356]

Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding Scope Link State PDUs (LSPs)", RFC 7356, DOI 10.17487/RFC7356, September 2014, <https://www.rfc-editor.org/info/rfc7356>.

[RFC7490]

Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N. So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)", RFC 7490, DOI 10.17487/RFC7490, April 2015, <https://www.rfc-editor.org/info/rfc7490>.

[RFC8400]

Chen, H., Liu, A., Saad, T., Xu, F., and L. Huang, "Extensions to RSVP-TE for Label Switched Path (LSP) Egress Protection", RFC 8400, DOI 10.17487/RFC8400, June 2018, <https://www.rfc-editor.org/info/rfc8400>.

[RFC8402]

Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, <https://www.rfc-editor.org/info/rfc8402>.

[RFC8665]

Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", RFC 8665, DOI 10.17487/RFC8665, December 2019, <https://www.rfc-editor.org/info/rfc8665>.

[RFC8667]

Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", RFC 8667, DOI 10.17487/RFC8667, December 2019, <https://www.rfc-editor.org/info/rfc8667>.

[RFC8679]

Shen, Y., Jeganathan, M., Decraene, B., Gredler, H., Michel, C., and H. Chen, "MPLS Egress Protection Framework", RFC 8679, DOI 10.17487/RFC8679, December 2019, <https://www.rfc-editor.org/info/rfc8679>.

[RFC8986]

Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, February 2021, <https://www.rfc-editor.org/info/rfc8986>.

8.2. Informative References

[I-D.hu-spring-segment-routing-proxy-forwarding]

Hu, Z., Chen, H., Yao, J., Bowers, C., Yongqing, and Yisong, "SR-TE Path Midpoint Restoration", Work in Progress, Internet-Draft, draft-hu-spring-segment-routing-proxy-forwarding-14, 29 April 2021, <https://www.ietf.org/archive/id/draft-hu-spring-segment-routing-proxy-forwarding-14.txt>.

[I-D.ietf-rtgwg-segment-routing-ti-lfa]

Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., Decraene, B., and D. Voyer, "Topology Independent Fast Reroute using Segment Routing", Work in Progress, Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-07, 29 June 2021, <https://www.ietf.org/archive/id/draft-ietf-rtgwg-segment-routing-ti-lfa-07.txt>.

[I-D.ietf-spring-segment-routing-policy]

Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", Work in Progress, Internet-Draft, draft-ietf-spring-segment-routing-policy-13, 28 May 2021, <https://www.ietf.org/archive/id/draft-ietf-spring-segment-routing-policy-13.txt>.

[RFC5226]

Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008, <https://www.rfc-editor.org/info/rfc5226>.

[RFC5462]

Andersson, L. and R. Asati, "Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field", RFC 5462, DOI 10.17487/RFC5462, February 2009, <https://www.rfc-editor.org/info/rfc5462>.