Abstract: Techniques are described for advertising constraint-based path computation (e.g., flexible-algorithm) through a constrained network topology. For example, a network device comprises a memory and one or more programmable processors operably coupled to the memory, wherein the one or more programmable processors are configured to generate a packet including a segment identifier (SID) offset, wherein the SID offset is an offset value associated with the flexible-algorithm. The one or more programmable processors of the network device are also configured to send, to at least one other network device of the plurality of network devices, the SID offset to enable the at least one other network device to derive a node segment identifier for the at least one other network device to participate in the flexible-algorithm.

Abstract: In general, various aspects of the techniques described in this disclosure provide a sequence number checksum for link state protocols. In one example, the disclosure describes an apparatus, such as a network device, having a control unit operative to obtain link state information describing links between pairs of the network devices in a network topology, the link state information being fragmented into a plurality of link state protocol (LSP) fragments; compute a sequence number checksum from sequence numbers of the link state protocol (LSP) fragments; receive an LSP data unit from another network device in the network; determine whether a sequence number checksum in the LSP data unit matches a sequence number checksum computed from the link state information; and configure a delay for processing the LSP data unit in response to determining a mismatch between the sequence number checksum of the LSP data unit and the sequence number checksum computed from the link state information.

Abstract: A first device may receive a packet that includes information identifying a path through a network. The first device may configure a header of the packet to include a first set of identifiers that identifies the path and the first device via which the packet was received. The first device may configure the header of the packet to include a second set of identifiers that identifies a set of devices associated with the path. The set of devices may be associated with providing the packet via a network. The first device may determine whether a counter associated with the first set of identifiers has been initialized. The first device may modify a value of the counter to record a metric. The first device may provide the packet to a second device. The first device may perform an action related to the packet or based on the value of the counter.

Abstract: Echo or traceroute functionality is supported in a path spanning multiple autonomous systems (ASes) having segment routing (SR) enabled, the path including an ingress node and an egress node, by: (a) obtaining a return label stack to reach the ingress node from either (A) the egress node, or (B) a transit node in the path; (b) obtaining a label stack to reach, from the ingress node, either (A) the egress node, or (B) the transit node; (c) generating a request message including the return label stack; and (d) sending the request message towards either (A) the egress node, or (B) the transit node using the label stack.

Abstract: Techniques are disclosed for a link state routing protocol adjacency state machine. The adjacency state machine ensures that first and second logical links using different networking protocols are established on a single physical link between two network devices prior to indicating adjacency between the network devices. In some examples, the adjacency state machine determines that both the first and second links are active in response to determining that hello messages are generated by both network devices for both links. In some examples, the adjacency state machine determines that both the first and second logical links are active upon expiration of a predetermined time corresponding to a time required for a duplicate address detection (DAD) operation to complete. In some examples, the first and second logical links use Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6), respectively.

Abstract: An improved traceroute mechanism for use in a label-switched path (LSP) is provided by (a) receiving, by a device in the LSP, an echo request message, wherein the echo request includes a label stack having a least one label, and wherein each of the at least one label has an associated time-to-live (TTL) value; (b) responsive to receiving the echo request, determining by the device, whether or not the device is a penultimate hop popping (PHP) device for the outermost label of the label stack; and (c) responsive to determining that the device is the PHP device for the outermost label of the label stack, (1) generating an echo reply message corresponding to the echo request message, wherein the echo reply message is encoded to indicate that the device is the PHP device for the outermost label of the label stack, and (2) sending the echo reply message back towards a source of the echo request message.

Abstract: In general, techniques are described by which to provide a scaled end-to-end view of link metrics to integrate multiple non-uniform Interior Gateway Protocol (“IGP”) domains. For example, an Accumulated Interior Gateway Protocol (“AIGP”) attribute, a non-transitive BGP attribute, which includes a link metric assigned to a link within a first IGP domain, is scaled to conform to a metric scale of the second IGP domain. The AIGP attribute may also add link metric assigned to a link within the second IGP domain and may add static metrics of non-IGP links connecting the IGP domains. An IGP domain may set its IGP to the scaled AIGP attribute such that the link metric may include a uniformly scaled end-to-end view of link metrics across the IGP domains. Additionally, a sham-link is assigned a metric value in accordance with the scaling techniques.

Abstract: Techniques are disclosed for a link state routing protocol adjacency state machine. The adjacency state machine ensures that first and second logical links using different networking protocols are established on a single physical link between two network devices prior to indicating adjacency between the network devices. In some examples, the adjacency state machine determines that both the first and second links are active in response to determining that hello messages are generated by both network devices for both links. In some examples, the adjacency state machine determines that both the first and second logical links are active upon expiration of a predetermined time corresponding to a time required for a duplicate address detection (DAD) operation to complete. In some examples, the first and second logical links use Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6), respectively.

Abstract: An improved traceroute mechanism for use in a label-switched path (LSP) is provided by (a) receiving, by a device in the LSP, an echo request message, wherein the echo request includes a label stack having a least one label, and wherein each of the at least one label has an associated time-to-live (TTL) value; (b) responsive to receiving the echo request, determining by the device, whether or not the device is a penultimate hop popping (PHP) device for the outermost label of the label stack; and (c) responsive to determining that the device is the PHP device for the outermost label of the label stack, (1) generating an echo reply message corresponding to the echo request message, wherein the echo reply message is encoded to indicate that the device is the PHP device for the outermost label of the label stack, and (2) sending the echo reply message back towards a source of the echo request message.

Abstract: A first device may receive a packet that includes information identifying a path through a network. The first device may configure a header of the packet to include a first set of identifiers that identifies the path and the first device via which the packet was received. The first device may configure the header of the packet to include a second set of identifiers that identifies a set of devices associated with the path. The set of devices may be associated with providing the packet via a network. The first device may determine whether a counter associated with the first set of identifiers has been initialized. The first device may modify a value of the counter to record a metric. The first device may provide the packet to a second device. The first device may perform an action related to the packet or based on the value of the counter.

Abstract: The use and processing of update messages (e.g., BGP UPDATEs) that bind (e.g., MPLS) labels to address prefixes is improved such that labels are used more efficiently, and/or such that such update messages can be processed more efficiently. A distance vector control signaling protocol (e.g., BGP) peer device receives a control plane message (e.g., BGP Update) from a downstream peer device, the control plane message including (1) a network address of the downstream device as a next hop value, (2) a prefix value, and (3) at least one label associated with the prefix value. Responsive to receiving the control plane message, the peer device generates a new control plane message including (1) a network address of the peer device as a next hop value, (2) the prefix value from the control plane message, and (3) a label stack including (i) the at least one label from the control plane message, and (ii) a local label associated with the peer device.

Abstract: A node may receive a network topology message that identifies a first association of a first segment identifier (SID), relating to a loosely routed segment of a network, and an address of a first terminal interface associated with the loosely routed segment, or a second association of a second SID, relating to a strictly routed segment of the network, and an address of a second terminal interface associated with the strictly routed segment. The node may generate an entry in a segment translation table based on the first association or the second association. The node may route, according to the segment translation table, an internet protocol (IP) payload packet that has been encapsulated using an IPv6 transport header that has been extended with a compressed routing header of variable length.

Abstract: Echo or traceroute functionality is supported in a path spanning multiple autonomous systems (ASes) having segment routing (SR) enabled, the path including an ingress node and an egress node, by: (a) obtaining a return label stack to reach the ingress node from either (A) the egress node, or (B) a transit node in the path; (b) obtaining a label stack to reach, from the ingress node, either (A) the egress node, or (B) the transit node; (c) generating a request message including the return label stack; and (d) sending the request message towards either (A) the egress node, or (B) the transit node using the label stack.

Abstract: Techniques are described for advertising constraint-based path computation (e.g., flexible-algorithm) through a constrained network topology. For example, a network device comprises a memory and one or more programmable processors operably coupled to the memory, wherein the one or more programmable processors are configured to generate a packet including a segment identifier (SID) offset, wherein the SID offset is an offset value associated with the flexible-algorithm. The one or more programmable processors of the network device are also configured to send, to at least one other network device of the plurality of network devices, the SID offset to enable the at least one other network device to derive a node segment identifier for the at least one other network device to participate in the flexible-algorithm.

Abstract: In general, techniques are described for conflict resolution in source packet routing in networking. For example, a first router receives a first advertisement originated in a first Interior Gateway Protocol (IGP) level. The first advertisement specifies a first prefix and a segment identifier (SID). The first router also receives a second advertisement originated in a second IGP level of the network. The second advertisement specifies a second prefix and the SID. Based on the first advertisement and the second advertisement specifying the same SID and based on the first IGP level having less visibility than the second IGP level, the first router selects the SID to be associated with a route to the first prefix.

Abstract: A first device may receive a packet that includes information identifying a path through a network. The first device may configure a header of the packet to include a first set of identifiers that identifies the path and the first device via which the packet was received. The first device may configure the header of the packet to include a second set of identifiers that identifies a set of devices associated with the path. The set of devices may be associated with providing the packet via a network. The first device may determine whether a counter associated with the first set of identifiers has been initialized. The first device may modify a value of the counter to record a metric. The first device may provide the packet to a second device. The first device may perform an action related to the packet or based on the value of the counter.

Abstract: A first network device detects a link down event associated with a second network device, where the link down event is detected by the first network device prior to being detected by a third network device, and the second network device is a designated network device of a network. The first network device starts a delay timer before processing the link down event, and detects an event that includes at least one of receipt, from the third network device, of a link state advertisement message based on the link down event, or an expiration of the delay timer. The first network device determines the first network device to be a new designated network device for the network based on detecting the event, and provides, to the third network device, information indicating that the first network device is the new designated network device for the network.

Abstract: Techniques are described for facilitating the inclusion of a non-flexible-algorithm router to be included in flexible-algorithm path computations. For example, a flexible-algorithm router advertises information associated with a non-flexible-algorithm router to other flexible-algorithm routers in the network such that the flexible-algorithm routers may include the non-flexible-algorithm router when computing a path based on flexible-algorithm. During path computation, if the router determines that its next-hop router is the non-flexible-algorithm router, the router may configure additional forwarding information to cause the router to steer traffic to the non-flexible-algorithm router.

Abstract: Techniques are described for facilitating the inclusion of a non-flexible-algorithm router to be included in flexible-algorithm path computations. For example, a flexible-algorithm router advertises information associated with a non-flexible-algorithm router to other flexible-algorithm routers in the network such that the flexible-algorithm routers may include the non-flexible-algorithm router when computing a path based on flexible-algorithm. During path computation, if the router determines that its next-hop router is the non-flexible-algorithm router, the router may configure additional forwarding information to cause the router to steer traffic to the non-flexible-algorithm router.

Abstract: A first network device detects a link down event associated with a second network device, where the link down event is detected by the first network device prior to being detected by a third network device, and the second network device is a designated network device of a network. The first network device starts a delay timer before processing the link down event, and detects an event that includes at least one of receipt, from the third network device, of a link state advertisement message based on the link down event, or an expiration of the delay timer. The first network device determines the first network device to be a new designated network device for the network based on detecting the event, and provides, to the third network device, information indicating that the first network device is the new designated network device for the network.