Path Ingress Protections

The fast protection of a transit node in each type of paths or tunnels have been proposed. For example, the fast protection of a transit node in a Segment Routing (SR) path or tunnel is described in . The fast protection of a transit node of a "Bit Index Explicit Replication" (BIER) Traffic Engineering (BIER-TE) path or tunnel is described in . presents extensions to RSVP-TE for the fast protection of the ingress node of a traffic engineering (TE) Label Switching Path (LSP). However, these documents do not discuss any protocol extensions for the fast protection of the ingress node of an SR path/tunnel, a BIER-TE path/tunnel, or other type of paths/tunnels. This document fills that void and specifies protocol extensions to Path Computation Element (PCE) communication Protocol (PCEP) and for fast protecting the ingress nodes of two types of paths: SR paths and BIER-TE paths. The extensions comprise a foundation for protecting the ingress nodes of different types of paths. Based on this, the ingress protection of a new type of paths can be easily supported. Ingress node and ingress, fast protection and protection, path ingress protection and ingress protection, SR path and SR tunnel, as well as BIER-TE path and BIER-TE tunnel will be used exchangeably in the following sections.

The following terminologies are used in this document. Path Computation Element or Path Computation Element server PCE communication Protocol Path Computation Client Bit Index Explicit Replication Bit Index Forwarding Table Customer Edge Provider Edge Traffic Engineering Segment Routing Loop-Free Alternate Topology Independent LFA Bidirectional Forwarding Detection Virtual Private Network Layer 3 VPN Forwarding Information Base

This section shows two examples of path ingress protection. One is SR path ingress protection, and the other is BIER-TE path ingress protection.

shows an example of protecting ingress PE1 of a SR path, which is from ingress PE1 to egress PE3 and represented by *** in the figure.

In normal operations, CE1 sends the traffic with destination PE3 to ingress PE1, which imports the traffic into the SR path. When CE1 detects the failure of ingress PE1, it switches the traffic to backup ingress PE2, which imports the traffic from CE1 into a backup SR path. The backup path is from the backup ingress PE2 to the egress PE3 and represented by ### in the figure. When the traffic is imported into the backup path, it is sent to the egress PE3 along the path.

shows an example of protecting ingress PE1 of a BIER-TE path, which is from ingress PE1 to egress nodes PE3 and PE4. This primary BIER-TE path is represented by *** in the figure. The ingress of the primary BIER-TE path is called primary ingress.

The backup BIER-TE path is from ingress PE2 to egress nodes PE3 and PE4, which is represented by ### in the figure. The ingress of the backup BIER-TE path is called backup ingress. In normal operations, CE1 sends the packets with a multicast group and source to ingress PE1, which imports/encapsulates the packets into the BIER-TE path through adding a BIER-TE header. The header contains the BIER-TE path from ingress PE1 to egress nodes PE3 and PE4. When CE1 detects the failure of ingress PE1 using a failure detection mechanism such as BFD, it switches the traffic to backup ingress PE2, which imports the traffic from CE1 into the backup BIER-TE path. When the traffic is imported into the backup path, it is sent to the egress nodes PE3 and PE4 along the path. Given the traffic source (e.g., CE1), ingress (e.g., PE1) and egresses (e.g., PE3 and PE4) of the primary BIER-TE path, the PCE computes a backup ingress (e.g., PE2), a backup BIER-TE path from the backup ingress to the egresses, and sends the backup BIER-TE path to the PCC of the backup ingress. It also sends the information about the backup ingress, the primary ingress and the traffic to the PCC of the traffic source (e.g., CE1). When the PCC of the traffic source receives the information about the backup ingress, the primary ingress and the traffic, it sets up the fast detection of the primary ingress failure and the switch over target backup ingress. This setup lets the traffic source node switch the traffic (to be sent to the primary ingress) to the backup ingress when it detects the failure of the primary ingress. When the PCC of the backup ingress receives the backup BIER-TE path, it adds a forwarding entry into its BIFT. This entry encapsulates the packets from the traffic source in the backup BIER-TE path. This makes the backup ingress send the traffic received from the traffic source to the egress nodes via the backup BIER-TE path.

This section describes the behavior of some nodes connected to the ingress before and after the ingress fails. These nodes are the traffic source (e.g., CE1) and the backup ingress (e.g., PE2). It presents three ways in which these nodes work together to protect the ingress. The first way is called source detect, where the traffic source is responsible for fast detecting the failure of the ingress. The second way is called backup ingress detect, in which the backup ingress is responsible for fast detecting the failure of the ingress. The third way is called both detect, where both the traffic source and the backup ingress are responsible for fast detecting the failure of the ingress.

In normal operations, i.e., before the failure of the ingress of a primary path such as a primary BIER-TE path, the traffic source sends the traffic to the ingress of the primary path. The backup ingress (e.g., PE2) is ready to import the traffic from the traffic source into the backup path such as the backup BIER-TE path installed. When the traffic source detects the failure of the ingress, it switches the traffic to the backup ingress, which delivers the traffic to the egress nodes of the path via the backup path.

The traffic source (e.g., CE1) always sends the traffic to both the ingress (e.g., PE1) of the primary path such as the primary BIER-TE path and the backup ingress (e.g., PE2). The backup ingress does not import any traffic from the traffic source into the backup path such as the backup BIER-TE path in normal operations. When it detects the failure of the ingress of the primary path, it imports the traffic from the source into the backup path. For the backup ingress to fast detect the failure of the primary ingress, it SHOULD directly connect to the primary ingress. When a PCE computes a backup ingress and a backup path, it SHOULD consider this.

In normal operations, i.e., before the failure of the ingress, the traffic source sends the traffic to the ingress of the primary path such as the primary BIER-TE path. When it detects the failure of the ingress, it switches the traffic to the backup ingress. The backup ingress does not import any traffic from the traffic source into the backup path such as the backup BIER-TE path in normal operations. When it detects the failure of the ingress of the primary path, it imports the traffic from the source into the backup path.

A PCC runs on each of the edge nodes such as PEs of a network normally. A PCE runs on a server as a controller to communicate with PCCs. PCE and PCCs work together to support protection for the ingress of a path. The path is a SR path, a BIER-TE path, or a path of another type.

When a PCE and a PCC running on a backup ingress establish a PCEP session between them, they exchange their capabilities of supporting protection for the ingress node of each of different types of paths. A new sub-TLV called INGRESS_PROTECTION_CAPABILITY is defined. It is included in the PATH_SETUP_TYPE_CAPABILITY TLV with PST = TBD1 (suggested value 2 for path ingress protection) in the OPEN object, which is exchanged in Open messages when a PCC and a PCE establish a PCEP session between them. Its format is illustrated below.

TBD2 is to be assigned by IANA. 4. 2 octets. MUST be set to zero in transmission and ignored on reception. 1 octet. Indicators for the types of paths whose ingress protections are supported. Two indicators are defined. S : S = 1 indicating that the ingress protection of a SR path is supported. B : B = 1 indicating that the ingress protection of a BIER-TE path is supported. 1 octet. Two flags are defined. D flag: A PCC sets this flag to 1 to indicate that it is able to detect its adjacent node's failure quickly. A flag: A PCE sets this flag to 1 to request a PCC to let the forwarding entry for the backup path/tunnel be Active. A PCC, which supports ingress protection for different types of paths, sends a PCE an Open message containing INGRESS_PROTECTION_CAPABILITY sub-TLV. This sub-TLV indicates that the PCC is capable of supporting the ingress protection for the types of paths. For example, if a PCC supports ingress protection for SR path and BIER-TE path, the PCC sends a PCE an Open message containing INGRESS_PROTECTION_CAPABILITY sub-TLV with S = 1 and B = 1. A PCE, which supports ingress protection for different types of paths, sends a PCC an Open message containing INGRESS_PROTECTION_CAPABILITY sub-TLV. This sub-TLV indicates that the PCE is capable of supporting the ingress protection for the types of paths. If both a PCC and a PCE support INGRESS_PROTECTION_CAPABILITY, each of the Open messages sent by the PCC and PCE contains PATH-SETUP-TYPE-CAPABILITY TLV with a PST list containing PST=TBD1 and an INGRESS_PROTECTION_CAPABILITY sub-TLV. If a PCE receives an Open message from a PCC without a INGRESS_PROTECTION_CAPABILITY sub-TLV indicating PCC's support for the ingress protection of a type of paths, then the PCE MUST not send the PCC any request for ingress protection of the type of paths. If a PCC receives an Open message from a PCE without a INGRESS_PROTECTION_CAPABILITY sub-TLV indicating PCE's support for the ingress protection of a type of paths, then the PCC MUST ignore any request for ingress protection of the type of paths from the PCE. If a PCC sets D flag to zero, then the PCE SHOULD send the PCC an Open message with A flag set to one and the fast detection of the failure of the primary ingress MUST be done by the traffic source. When the PCE sends the PCC a message for initiating a backup path, the PCC MUST let the forwarding entry for the backup path be Active.

When a PCE and a PCC running on a traffic source node establish a PCEP session between them, they exchange their capabilities of supporting ingress protection. The PCECC-CAPABILITY sub-TLV defined in is included in the OPEN object in the PATH-SETUP-TYPE-CAPABILITY TLV, which is exchanged in Open messages when a PCC and a PCE establish a PCEP session between them. A new flag bit P is defined in the Flags field of the PCECC-CAPABILITY sub-TLV: P flag (for Ingress Protection): if set to 1 by a PCEP speaker, the P flag indicates that the PCEP speaker supports and is willing to handle the PCECC based central controller instructions for ingress protection. The bit MUST be set to 1 by both a PCC and a PCE for the PCECC ingress protection instruction download/report on a PCEP session.

This section specifies the extensions to PCEP for the backup ingress and the traffic source. The extensions let the traffic source fast detect the failure of the primary ingress and switch the traffic to the backup ingress when the traffic source detects the failure of the primary ingress, or always send the traffic to both the primary ingress and the backup ingress. The extensions let the backup ingress always import the traffic received from the traffic source with possible service ID into the backup path, or import the traffic with possible service ID into the backup path when the backup ingress detects the failure of the primary ingress. The following lists the combinations of Si and Bi (i = 1,2) for different ways of failure detects. S1 and B1. S2 and B2. S1 and B2.

For the packets from the traffic source, if the primary ingress (i.e., the ingress of the primary path) encapsulates the packets with a service ID or label into the path, the backup ingress MUST have this service ID or label and encapsulates the packets with the service ID or label into the backup path when the primary ingress fails. If the backup ingress is requested to detect the failure of the primary ingress, it MUST have the information about the primary ingress such as the address of the primary ingress. A new sub-TLV called INGRESS_PROTECTION is defined. When a PCE sends a PCC a PCInitiate message for initiating a backup path to protect the primary ingress node of a primary path, the message contains this TLV in the RP/SRP object. Its format is illustrated below.

TBD3 is to be assigned by IANA. Variable. 2 octets. MUST be set to zero in transmission and ignored on reception. 2 octets. One flag is defined. A flag bit: it is set to 1 or 0 by PCE. 1 is to request the backup ingress to let the forwarding entry for the backup path be Active always. In this case, the traffic source detects the failure of the primary ingress and switches the traffic to the backup ingress when it detects the failure. 0 is to request the backup ingress to detect the failure of the primary ingress and let the forwarding entry for the backup path be Active when the primary ingress fails. In this case, the TLV includes the primary ingress address in a Primary-Ingress sub-TLV. The traffic source can send the traffic to both the primary ingress and the backup ingress. It may switch the traffic to the backup ingress from the primary ingress when it detects the failure of the primary ingress. Three optional sub-TLVs are defined: Primary-Ingress sub-TLV, Service sub-TLV, and Traffic-Description sub-TLV. The Traffic-Description sub-TLV describes the traffic to be imported into the backup SR path. The Multicast Flow Specification TLV for IPv4 or IPv6, which is defined in , is used as a sub-TLV to indicate the traffic to be imported into the backup BIER-TE path.

A Primary-Ingress sub-TLV indicates the IP address of the primary ingress node of a primary path. It has two formats: one for primary ingress node IPv4 address and the other for primary ingress node IPv6 address, which are illustrated below.

TBD4 is to be assigned by IANA. 4. 4 octets. It represents an IPv4 host address of the primary ingress node of a path.

TBD5 is to be assigned by IANA. 16. 16 octets. It represents an IPv6 host address of the primary ingress node of a path.

A Service sub-TLV contains a service ID or label to be added into a packet to be carried by a path. It has two formats: one for the service identified by a label and the other for the service identified by a service identifier (ID) of 32 or 128 bits, which are illustrated below.

TBD6 is to be assigned by IANA. 4. the least significant 20 bits. It represents a label of 20 bits.

TBD7 is to be assigned by IANA. 4 or 16. 4 or 16 octets. It represents Identifier (ID) of a service in 4 or 16 octets.

A Traffic-Description sub-TLV describes the traffic to be imported into a backup SR path. Its format is illustrated below.

TBD8 is to be assigned by IANA. Variable. Two optional sub-TLVs are defined. One is FEC sub-TLV and the other interface sub-TLV. A FEC sub-TLV describes the traffic to be imported into the backup path. It is an IP prefix with an optional virtual network ID. It has two formats: one for IPv4 and the other for IPv6, which are illustrated below.

TBD9 is to be assigned by IANA. Variable. Indicates the length of the IPv4 Prefix. IPv4 Prefix rounded to octets. 2 octets. This is optional. It indicates the ID of a virtual network.

TBDa is to be assigned by IANA. Variable. Indicates the length of the IPv6 Prefix. IPv6 Prefix rounded to octets. 2 octets. This is optional. It indicates the ID of a virtual network. An Interface sub-TLV indicates the interface from which the traffic is received and imported into the backup path. It has three formats: one for interface index, the other two for IPv4 and IPv6 address, which are illustrated below.

TBDb is to be assigned by IANA. 4. 4 octets. It indicates the index of an interface.

TBDc is to be assigned by IANA. 4. 4 octets. It represents the IPv4 address of an interface.

TBDd is to be assigned by IANA. 16. 16 octets. It represents the IPv6 address of an interface.

If the traffic source is requested to detect the failure of the primary ingress and switch the traffic (to be sent to the primary ingress) to the backup ingress when the primary ingress fails, it MUST have the information about the backup ingress, the primary ingress and the traffic. This information may be transferred via a CCI object for INGRESS-PROTECTION to the PCC of the traffic source node from a PCE. If the traffic source PCC does not accept the request from the PCE or support the extensions, the PCE SHOULD have the information about the behavior of the traffic source configured such as whether it detects the failure of the primary ingress. Based on the information, the PCE instructs the backup ingress accordingly. The Central Control Instructions (CCI) Object is defined in for a PCE as a controller to send instructions for LSPs to a PCC. This document defines a new object-type (TBDt) for ingress protection based on the CCI object. The body of the object with the new object-type is illustrated below. The object may be in PCRpt, PCUpd, or PCInitiate message.

It is the same as described in . Two flag bits D and B are defined as follows: D = 1 instructs the PCC of the traffic source to Detect the failure of the primary ingress and switch the traffic to the backup ingress when it detects the failure. B = 1 instructs the PCC of the traffic source to send the traffic to Both the primary ingress and the backup ingress. Primary ingress TLV, backup ingress TLV, Traffic-Description TLV or Multicast Flow Specification TLV. The primary ingress sub-TLV defined above is used as a TLV to contain the information about the primary ingress in the object. The Traffic-Description sub-TLV defined above is used as a TLV to contain the information about the traffic for a SR path in the object. The Multicast Flow Specification TLV for IPv4 or IPv6, which is defined in , is used to contain the information about the traffic for a BIER-TE path in the object. A new TLV, called backup ingress TLV, is defined to contain the information about the backup ingress in the object.

A Backup-Ingress TLV indicates the IP address of the ingress node of a backup path. It has two formats: one for backup ingress node IPv4 address and the other for backup ingress node IPv6 address, which are illustrated below. They have the same format as the Primary-Ingress sub-TLVs.

TBDe is to be assigned by IANA. 4. 4 octets. It represents an IPv4 host address of the backup ingress.

TBDf is to be assigned by IANA. 16. 16 octets. It represents an IPv6 host address of the backup ingress node.

TBD

The authors of this document would like to thank Dhruv Dhody and Robin Li for their reviews and comments.

TBD