A method, node and system for performing optimal routing in an inter-region SRMPLS IGP network

Abstract

Disclosed are a method, a source node, an area border node and a system thereof for performing optimal routing in an inter-area IGP network based on an SR-MPLS flexible algorithm process. The method includes: each of at least two area border nodes in the IGP network advertises an algorithm-specific metric associated with a destination node to a source node, wherein the IGP network includes a first area and a second area, the destination node is from a first node set of the first area, and the source node is from a second node set of the second area; the source node calculates each inter-area path metric associated with a path to the destination node via a corresponding area border node; based on each calculated inter-area path metric, the source node determines an optimal path to the destination node via one of the at least two area border nodes.

Description

[0001] This application is a divisional application of a Chinese patent application with application number 202080022704.2 and invention title "A Method, Node and System for Performing Optimal Routing in an Inter-Area SRMPLS IGP Network" filed on March 20, 2020, the entire content of which is incorporated herein by reference.

[0002] Cross-reference to related applications

[0003] This application relates to Indian Application No. IN201931010956, filed on March 20, 2019, with the invention title "A Method for Optimal Routing in an Inter-Area SRMPLS IGP Network, Nodes and System Thereof (METHOD FOR OPTIMAL ROUTING IN AN INTER-AREA SRMPLS IGP NETWORK, NODES AND SYSTEM THEREOF)", and claims the benefit thereof. The entire content of the prior application is incorporated herein by reference. Technical field

[0004] The subject matter described herein generally relates to segment routing, and more particularly, to a segment routing-flexible algorithm scheme for an inter-area interior gateway protocol (IGP) network. Background art

[0005] Segment Routing (SR) divides the network into "segments", where each node and link can be assigned a segment identifier or SID. Each node advertises the segment identifier using standard routing protocol extensions (such as ISIS / OSPF or BGP) without running an additional label distribution protocol. The prefix SID represents the prefix segment attached to the Interior Gateway Protocol (IGP) prefix. Additionally, the IP loopback address can be used to distinguish SR nodes within the vendor system. Packets addressed by a given SID are typically transmitted along the shortest path, for example, the shortest path to the network node associated with the SID. The loopback address can be used in link state protocols or amendments such as Open Shortest Path First (OSPF), Intermediate System to Intermediate System (IS-IS), etc., and thus can be run in the control plane of SR nodes (nodes adopting SR) to identify the outgoing interface of the shortest path for each node. SR nodes can advertise their SIDs in the vendor network using one or more protocols such as the Interior Gateway Protocol (IGP).

[0006] Traditionally, IGP protocols calculate the best path in the network based on the IGP metrics assigned to the links. In many cases, traffic engineering (TE) can cause packets to be forwarded along paths other than the shortest path. In many network deployments, RSVP-TE or segment-routing-based traffic engineering is used to force traffic through a path that is calculated using a metric or constraint different from the shortest IGP path. TE constrained paths need to be added to the forwarding table or used as a replacement for the IGP calculated path. The SR-TE policy path is a list of segment identifiers (SIDs), and the MPLS label stack is derived from the segment list. TE constraints are named flexible algorithm definition (FAD) and advertised in the IGP, enabling the IGP to perform constraint-based path calculation. The flexible algorithm path is represented by only one SID, and the MPLS label is derived from the SID and downloaded to the MPLS forwarding table.

[0007] The Internet Engineering Task Force (IETF) published an Internet draft on November 12, 2018, titled "IGP Flexible Algorithm draft-ietf-lsr-flex-algo-01.text", which describes a method of using "Segment Routing Prefix-SIDs" to steer packets along a constraint-based path. This document describes an extended set of ISIS, OSPFv2, and OSPFv3, enabling routers to send TLVs to compute the best path in a constrained topology. This document also describes a method by which a router uses IGP to associate one or more Segment Routing Prefix-SIDs with a specific flexible algorithm. Then, each such prefix-SID represents a path computed according to the identified flexible algorithm. A specific combination of computation type, metric type, and constraints is called a "flexible algorithm definition". A router that sends such a set of TLVs also specifies a specific value, the flexible algorithm, for the specific combination of computation type, metric type, and constraints.

[0008] However, the computation of any IGP shortest path tree is limited to a single area. Similarly, the flexible algorithm computation based on this document is also limited to a single area. In particular, this document stipulates that the selection of the egress L1 / L2 router (ABR in OSPF) will be based on the best path for a given flexible algorithm in the local area, and this egress L1 / L2 router (ABR in OSPF) will be responsible for computing the best flexible algorithm-specific path for the next area. This may result in a sub-optimal end-to-end path based on flexible algorithm constraints. If the best end-to-end path for a given flexible algorithm needs to be applied to inter-area destinations, the paths to these destinations need to be computed by an entity that has all the topological information of all areas. The currently specified solution requires a Path Computation Element (PCE) or any similar external controller to compute the inter-area path, and the PCE can access the node information of all areas.

[0009] In summary, without using a PCE, a Segment Routing flexible algorithm solution for optimizing inter-area paths is needed. Summary of the Invention

[0010] The summary of the invention aims to introduce a method for optimal routing using the Segment Routing - Flexible Algorithm protocol in an inter-area IGP network and related concepts of network nodes to identify the best end-to-end path.

[0011] The first aspect of the present invention provides a method for optimal routing using segment routing - flexible algorithm protocol in an inter - area IGP network. The inter - area IGP network includes a first area and a second area. The first area includes a first node set and at least two area border routers (ABRs). The second area includes a second node set and the at least two area border routers. The method includes: each of the at least two area border routers advertises an algorithm - specific metric associated with a destination node to a source node, where the destination node is from the first node set and the source node is from the second node set. The method further includes: the source node calculates each inter - area path metric associated with a path to the destination node via a corresponding area border router, each inter - area path metric being based on the algorithm - specific metric advertised by the corresponding area border router. The method further includes: based on each calculated inter - area path metric, the source node determines an optimal path to the destination node via one of the at least two ABR nodes. The method further includes: forwarding a packet from the source node to the destination node through the determined path.

[0012] The second aspect of the present invention provides a method for optimal routing using segment routing - flexible algorithm protocol by a source node in an inter - area IGP network. The inter - area IGP network includes a first area and a second area. The first area includes a first node set and at least two area border routers, and the first node set includes the source node. The second area includes a second node set and the at least two area border routers. The method includes: receiving from each of the at least two area border routers an algorithm - specific metric associated with a destination node, where the destination node is from the first node set. The method further includes: calculating each inter - area path metric associated with a path to the destination node via a corresponding area border router, each inter - area path metric being based on the algorithm - specific metric advertised by the corresponding area border router. The method further includes: based on each calculated inter - area path metric, determining an optimal path to the destination node via one of the at least two ABR nodes. The method further includes: forwarding a packet from the source node to the destination node through the determined path.

[0013] A third aspect of the present invention provides a method for performing optimal routing in an inter-regional IGP network using a segmented routing-flexible algorithm protocol by an area border node. The inter-regional IGP network includes a first area and a second area, the first area including a first node set, the area border node, and at least one other area border node, and the second area including a second node set, the area border node, and at least one other area border node. The method includes: notifying a source node of an algorithm-specific metric associated with a destination node, the destination node being from the first node set, and the source node being from the second node set. Based on the algorithm-specific metric notified by the corresponding area border node, the source node calculates an inter-regional path metric associated with a path from the source node to the destination node, the path including the corresponding area border node. The method includes: when the source node determines that the path is the optimal path, receiving a message to be forwarded to the destination node from the source node; and forwarding the message to the destination node via the determined path. The source node determines the optimal path based on: the inter-area path metric associated with the path via the corresponding area boundary node and each inter-area path metric calculated by the source node, wherein each inter-area path metric is associated with the path to the destination node via the at least one other area boundary node.

[0014] A fourth aspect of the present invention provides a source node for performing optimal routing to a destination node in an inter-area IGP network. The inter-area IGP network includes a first area and a second area, the first area including a first node set and at least two area border nodes, the first node set including the source node, the second area including a second node set and the at least two area border nodes, the second node set including the destination node. The source node includes a receiving unit for receiving, from each of the at least two area border nodes, a notification of an algorithm-specific metric associated with the destination node. The source node also includes a path metric calculation unit for calculating each inter-area path metric associated with a path to the destination node via a corresponding area border node, each inter-area path metric being based on the algorithm-specific metric announced by the corresponding area border node. The source node also includes a path determination unit for determining, based on each calculated inter-area path metric, an optimal path to the destination node via one of the at least two area border nodes. The source node also includes a message forwarding unit for forwarding a message from the source node to the destination node via the determined path.

[0015] A fifth aspect of the present invention provides an area border node for performing optimal routing in an inter-area IGP network. The inter-area IGP network includes a first area and a second area, the first area including a first node set, the area border node, and at least one other area border node, and the second area including a second node set, the area border node, and at least one other area border node. The area border node includes a sending unit for notifying a source node of an algorithm-specific metric associated with a destination node from the first node set and a source node from the second node set. Based on the algorithm-specific metric notified by the corresponding area border node, the source node calculates an inter-area path metric associated with a path from the source node to the destination node, the path including the corresponding area border node. The area border node also includes a receiving unit for receiving, when the source node determines that the path is the optimal path to the destination node, a message to be forwarded to the destination node from the source node. The area border node also includes a message forwarding unit for forwarding the message to the destination node via the determined path. The source node determines the optimal path based on: the inter-area path metric associated with the path via the corresponding area boundary node and each inter-area path metric calculated by the source node, wherein each inter-area path metric is associated with the path to the destination node via the at least one other area boundary node. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The detailed description is described with reference to the accompanying drawings. Obviously, the drawings in the following description only illustrate some embodiments of the present invention.

[0017] Figure 1 The present invention illustrates a network deployment scenario of SR-MPLS in an inter-regional IGP network implementing a flexible algorithm process according to an embodiment of the present invention.

[0018] Figure 2 The present invention illustrates a method for forwarding packets using an SR-MPLS flexible algorithm process in an inter-regional IGP network according to an embodiment of the present invention.

[0019] Figure 3 The present invention illustrates a method for forwarding a message from a source node in one area to a destination node in another area using an SR-MPLS flexible algorithm process in an inter-area IGP network according to an embodiment of the present invention.

[0020] Figure 4A A block diagram illustrating components associated with a source device in one area of an inter-area IGP network, configured to forward a packet to a destination node in another area of the inter-area IGP network using an SR-MPLS flexible algorithm process, according to an embodiment of the present invention.

[0021] Figure 4B A block diagram of components associated with a regional boundary node according to an embodiment of the present invention is shown. The regional boundary node is located in an inter-regional IGP network and is used to forward packets from a source node in one region of the inter-regional IGP network to a destination node in another region by adopting an SR-MPLS flexible algorithm process;

[0022] Figure 4C A block diagram of components associated with an optimal routing system according to an embodiment of the present invention is shown. The system is located in an inter-regional IGP network and is used to forward packets from a source node in one region of the inter-regional IGP network to a destination node in another region by adopting an SR-MPLS flexible algorithm process;

[0023] Figure 5 A block diagram of a typical general router according to an embodiment of the present invention is shown. The router participates in an inter-regional IGP network by adopting an SR-MPLS flexible algorithm process.

[0024] It should be understood that the drawings are for illustrative purposes of the concepts of the present invention and are not necessarily drawn to scale. Detailed implementation manners

[0025] The present invention can be implemented in many ways, including being implemented as a process, a device, a system, a computer-readable medium such as a computer-readable storage medium, or a computer network in which program instructions are sent via an optical or electronic communication link. In this specification, these implementation manners or any other form that the present invention can take can be referred to as technologies. Generally, the order of steps of the disclosed processes can be changed within the scope of the present invention.

[0026] The following provides a detailed description of one or more embodiments of the present invention and the drawings illustrating the principles of the present invention. The present invention is described in conjunction with these embodiments, but the present invention is not limited to any embodiment. The scope of the present invention is only limited by the claims, and the present invention includes many alternatives, modifications, and equivalents. To provide a thorough understanding of the present invention, many specific details are set forth in the following description. These details are provided for illustrative purposes, and the present invention can be implemented according to the claims without some or all of these specific details. For the sake of clear description, the technical materials known in the technical field related to the present invention are not described in detail, so as to avoid unnecessarily obscuring the present invention.

[0027] Many specific details are set forth in the following description to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the art will understand that the present invention can be practiced without these specific details. In other instances, well-known methods, processes, components are not described in detail so as not to obscure the present invention.

[0028] Although embodiments of the present invention are not limited thereto, when terms such as "processing", "calculating", "operating", "determining", "establishing", "analyzing", "checking", etc. are used, they may refer to operations and / or processes of a computer, a computing platform, a computing system, or other electronic computing devices, which manipulate and / or transform data represented as physical (e.g., electronic) quantities in computer registers and / or memories into other data similarly represented as physical quantities in computer registers and / or memories or other non-transitory information storage media, and the other non-transitory information storage media may store instructions for executing the operations and / or processes.

[0029] Although embodiments of the present invention are not limited thereto, as used herein, the terms "plurality" and "multiple" may include "several" or "two or more", etc. The terms "plurality" or "multiple" may be used throughout the specification to describe two or more components, devices, elements, units, parameters, etc. Unless explicitly stated, the method embodiments described herein are not limited to a particular order or sequence. In addition, some of the described method embodiments or their elements may occur or be executed simultaneously, at the same point in time, or in parallel.

[0030] When needed, some embodiments of the present invention may be explained with the aid of exemplary figures and one or more examples. However, providing such exemplary figures and examples is only for better understanding of the present invention and should not be construed as a limitation on the scope of the present invention.

[0031] The technical solution of the present invention can be applied to an interior gateway protocol (IGP) network including a first region (also referred to as region 0 in the present invention) and a second region (also referred to as region 1 in the present invention). Specifically, the present invention aims to determine the optimal path or the best path for forwarding data packets in an interior gateway protocol (IGP) inter-region network.

[0032] According to an embodiment of the present invention, in the deployment of an inter-region IGP network, segment routing (SR)-multiprotocol label switching (MPLS)-based traffic engineering is used to force traffic to pass through the best or optimal path using different metrics or constraints. The path determined by constrained SR-TE can be added to the forwarding table of MPLS.

[0033] According to a preferred embodiment of the present invention, the topological constraints of the IGP network can be determined by a flexible algorithm definition. The flexible algorithm definition is a specific combination of calculation type, metric type, and specific constraints, which is used to determine the best or optimal path for forwarding data packets in the IGP network. Nodes participating in the IGP network (also referred to as routers in the present invention) send messages to at least one other node in the internal area of the IGP network, and the messages include information indicating the flexible algorithm definition. Such messages are in the form of a set of type-length-values (TLVs) indicating the flexible algorithm definition. When the nodes in the intra-area network forward this set of TLVs to other nodes in the intra-area network, they also assign a specific value, called "flexible algorithm". This specific value is a numerical identifier between 128 and 255.

[0034] In addition, the node associates one or more SR prefix-segment identifiers (segment identifiers, SIDs) with the specific flexible algorithm currently adopted. Then, each such prefix-SID represents a path calculated according to the identified flexible algorithm.

[0035] The present invention provides a technical solution for identifying the optimal path or best path in an inter-area IGP network without using an external controller, which is traditionally used to deploy a process based on SR-MPLS constraints in the IGP network to calculate the best path. The inter-area IGP network includes a first area and a second area, and the first area and the second area respectively include a first set of nodes and a second set of nodes. Among them, the first set of nodes in the first area may not have topological visibility of the second set of nodes in the second area. To achieve the optimal inter-area path of the SR-MPLS flexible algorithm, area border nodes, such as area border routers (ABRs) in OSPF or L2 routers in ISIS, announce / leak the flexible algorithm specific metric along with the flexible algorithm segment identifier (segment identifier, SID) for their respective destination routers (e.g., Prefix or Route), so that the source node in the second area can calculate the optimal end-to-end path to the prefix SID across the area, that is, reach the destination node associated with the prefix SID in the first area.

[0036] To deploy the above technical solution, the present invention also provides an extended set of Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (ISIS) as the routing protocol for the inter-area IGP network. The extended sets of ISIS, OSPFv2, and OSPFv3 in the above description of the present invention are used by the area border nodes to advertise / leak the flexible algorithm metric and flexible algorithm SID of the corresponding destination node in one area to the source node in another area. Now, the deployment of the SR-MPLS flexible algorithm in the inter-area IGP network described according to the present invention will be explained through Figure 1 and Figure 2 The deployment of the SR-MPLS flexible algorithm in the inter-area IGP network described according to the present invention will be explained through

[0037] Figure 1 FIG. shows a network deployment scenario of the SR-MPLS flexible algorithm in the inter-area IGP network 100 according to an embodiment of the present invention. The IGP network 100 includes a first area 101 (i.e., area 0) and a second area 102 (i.e., area 1). The first area (area 0) may be a backbone area, and the second area (area 1) may be a non-backbone area, but it should not be construed as a limitation to the present invention. Here, an area refers to a logical group of networks, routers, and links with the same area number, and may also be referred to as an internal area. The first area 101 includes routers RT 8, RT 7, RT 5, RT 4, and RT 6, and the second area 102 includes routers RT 1, RT 2, RT 4, and RT 3. The first area 101 and the second area 102 have a common area border router (ABR), that is, a router placed at the boundary between the first area 101 and the second area 102. In the IGP network 100, RT 4 and RT 5 are ABRs.

[0038] As described above, each prefix SID associated with a router or segment is algorithm-related. Each node within a region advertises its algorithm in a specific form of an SR-algorithm TLV. The deployed flexible algorithms are defined by the operator and may include specific minimized metrics such as IGP overhead, latency, etc. and / or exclude certain link attributes. As an example, Operator 1 defines Flex-Algo128 as "green that minimizes IGP metric and avoids link affinity", and Operator 2 defines Flex-Algo128 as "blue that minimizes latency metric and avoids link affinity". Each node within a region advertises the Flex-Algo it participates in to other nodes in the same region. When the node advertises the Flex-Algo it participates in, it also advertises the prefix-SID associated with that Flex-Algo. As an example, RT 8 in Region 0 advertises the loopback prefix 81.81.81.81, prefix-SID 81, and algorithm-ID 128 (i.e., the defined flexible algorithm) to RT 6, RT 4, RT 7, and RT 5.

[0039] The shortest path or the best path in the regional topology within an IGP region is a metric defined by the flexible algorithm. The metric can be the IGP metric, i.e., the calculated shortest path, or the TE metric or latency. Based on the calculated metric, the prefix-SID associated with the destination is updated in the MPLS forwarding table.

[0040] According to an embodiment of the present invention, the ABR leaks / advertises the metric associated with the destination prefix SID and the defined flexible algorithm to the source node in another region, enabling the source node to calculate the best path in the topology of the inter-regional IGP network.

[0041] As an example, Figure 1 The link-TE metrics configured between each node are shown: the link-TE metric between RT 8 and RT 6 is 10, the link-TE metric between RT8 and RT6 is 10, the link-TE metric between RT 6 and RT 4 is 10, the link-TE metric between RT 4 and RT 2 is 10, the link-TE metric between RT 2 and RT 1 is 10, the link-TE metric between RT 8 and RT 7 is 10, the link-TE metric between RT 7 and RT 5 is 50, the link-TE metric between RT 5 and RT 3 is 10, and the link-TE metric between RT 3 and RT2 is 10. In addition, the link metric between RT 4 and RT 5 is indicated as 50.

[0042] All routers in the inter-area IGP network participate in Algorithm-ID 128. Two ABRs, namely RT 4 and RT5, advertise the Algorithm-ID, as well as the prefix SID and TE-metric associated with the destination node in Area 0, to the nodes in Area 1 respectively.

[0043] In a specific example, the destination node is RT 8, which is configured with a loopback prefix 81.81.81.81, a prefix SID 81, and a supported flexible algorithm 128. To calculate the best inter-area path according to the defined flexible algorithm, ABR RT 4 leaks the TE-metric 20 to Area 1 to reach the destination node RT 8, that is, the prefix 81.81.81.81. The TE-metric 20 is derived from the hop from RT8 to RT 6 (TE-metric is 10) and the hop from RT 6 to RT 4 (TE-metric is 10). Similarly, ABR RT 5 leaks the TE-metric 60 to Area 1 to reach the destination node RT 8, that is, the prefix 81.81.81.81. The TE-metric 60 is derived from the hop from RT8 to RT 7 (TE-metric is 10) and the hop from RT 7 to RT 5 (TE-metric is 50).

[0044] Each router in Area 1 calculates the inter-area path metric using the leaked SID-metric, that is, the path metric to the ABR + the metric leaked by the ABR. For example, RT 1 reaches the prefix 81.81.81.81 via RT 4, and calculates the inter-area path metric as 40. The inter-area path metric 40 is derived from the metric leaked by ABR RT 4 (i.e., 20), the TE-metric associated with the hop between RT 4 and RT 2 (i.e., 10), and the sum of the TE-metrics associated with the hop between RT 2 and RT 1. Similarly, RT 1 reaches the prefix 81.81.81.81 via RT 5, and calculates the inter-area path metric as 80. The inter-area path metric 80 is derived from the metric leaked by ABR RT 5 (i.e., 60), the TE-metric associated with the hop between RT 5 and RT 3 (i.e., 10), and the sum of the TE-metrics associated with the hop between RT 3 and RT 1.

[0045] Based on the inter-area paths calculated via each ABR (i.e., RT 4 and RT 5), the source node determines the optimal path or the best path to reach the prefix 81.81.81.81. In this example, RT 1 selects to reach the prefix 81.81.81.81 via ABR RT 4 based on the cost. Although the TE-metric is used in this example, it should not be construed as a limitation of the present invention. The determination of the best path is based on algorithm-specific metrics, which can be based on delay or IGP cost, etc.

[0046] The optimal path or best path includes one of the two ABRs, which is RT 4 in this example. Additionally, the calculation of the inter-area path metric includes the metric associated with one or more hops from the source node to the corresponding selected ABR. In this example, RT 1 selects the next hop RT 2 to reach the ABR RT 4.

[0047] After determining the path, the corresponding labels of the router are derived from their respective SIDs and downloaded into the forwarding table of RT 1 to reach the prefix 81.81.81.81. Thereafter, in the inter-area IGP network 100, the data packet from the source node, i.e., RT 1, is forwarded to the destination node, i.e., RT 8, via the best path through RT 4. The forwarding of the data packet uses the MPLS routing protocol.

[0048] Figure 2 A flowchart shows the forwarding of a data packet from the source node RT 1 in area 1 to the destination node RT 8 in area 0 via the selected ABR, i.e., ABR RT 4 or ABR 5.

[0049] In step 201, ABR RT 4 and RT 5 advertise / leak the algorithm-SID specific metric of the destination node, as well as the prefix-SID and algorithm-ID of the destination node, to area 1.

[0050] In step 202, based on the leakage information from the corresponding ABR, the source node RT 1 in area 1 calculates the corresponding inter-area path metric to reach the destination node RT 8.

[0051] In step 203, based on the inter-area path metric calculated for each corresponding ABR, the source node RT 1 selects an ABR, i.e., ABR RT 4 or ABR RT 5, to reach the destination node RT 8, where the optimal path or best path includes the selected ABR. Additionally, based on the calculation of the selected ABR and the intra-area path metric, the next hop of the source node RT 1 is selected.

[0052] According to the above example, if ABR RT 4 is selected, when the source node RT 1 determines that the path through ABR RT 4 is the optimal path or best path to reach the destination node RT 8, ABR RT 4 receives the packet to be forwarded to the destination node RT 8 from the source node RT 6. The source node RT 1 determines the optimal path based on: the inter-area path metric associated with the path through the corresponding area border node RT 4 and each inter-area path metric calculated by the source node RT 1. Each inter-area path metric is associated with a path to reach the destination node RT 8 through at least one other ABR RT 5.

[0053] In step 204, the data packet is forwarded from the source node to the destination node via the optimal or best path of the selected ABR. In the above example, ABR RT 4 receives the packet from source node RT 1 and further forwards the packet to destination node RT 8 via the determined path.

[0054] According to a further embodiment of the present application, the advertisement from the area border node to area 1 uses a specific format called TLV. The message including the TLV is sent from the area border node to each source node in area 1. The present application provides an extended set of OSPF (v2 and v3) and ISIS, enabling the area border node to send TLVs so as to advertise metrics in the inter-area IGP network in the above manner.

[0055] To advertise / leak algorithm-SID specific metrics, the inventive concept proposes extensions to IGP (OSPF and ISIS) as follows:

[0056] (A) OSPF extension: "Prefix SRMPLS algorithm metric sub-TLV."

[0057] Encode the algorithm-SID metric into a new "SRMPLS algorithm metric sub-TLV" as a sub-TLV of "OSPF extended prefix TLV" and "OSPFv3 E-Inter-Area-Prefix-LSA TLV".

[0058]

[0059] Where:

[0060] Type represents the value of the link metric type used in the calculation, which can be IGP metric, link delay or TE metric.

[0061] Length represents the variable value, depending on the included sub-TLV.

[0062] Algorithm represents a flexible algorithm.

[0063] Reserved represents the reserved bit.

[0064] Metric represents the algorithm-specific metric, for example, Figure 1 the TE-metric in the example shown in.

[0065] (B) ISIS extension: "Prefix SRMPLS algorithm metric sub-TLV"

[0066] Encode the algorithm-SID metric into a new "SRMPLS algorithm metric sub-TLV" as a sub-TLV in any of the following ISIS TLVs:

[0067] TLV-135 (Extended IPv4 Reachability) defined in RFC5305.

[0068] TLV-235 (Multi-Topology IPv4 Reachability) defined in RFC5120.

[0069] TLV-236 (Extended IPv6 Reachability) defined in RFC5308.

[0070] TLV-237 (Multi-Topology IPv6 Reachability) defined in RFC5120.

[0071]

[0072] Where:

[0073] Type represents the value of the link metric type used in the calculation, which can be IGP metric, link delay or TE metric.

[0074] Length represents the variable value, depending on the contained sub-TLV.

[0075] Algorithm represents a flexible algorithm.

[0076] Reserved represents the reserved bit.

[0077] Metric represents the algorithm-specific metric, for example, Figure 1 the TE-metric in the example shown in.

[0078] Figure 3 represents Method 300 for forwarding data packets in an inter-area IGP network. For example, the inter-area network 100 may include the first area 101 and the second area 102 as shown in Figure 1 shown.

[0079] In step 301, each of the two area border nodes in the first area 101 and the second area 102 advertises the algorithm-specific metric associated with the destination node to the second node set in the second area 102, where the destination node is from the first node set in the first area 101. The area border node also advertises the prefix SID of the destination node and the algorithm-specific metric. The area border node may also advertise the flexible algorithm in which the destination node participates.

[0080] In one implementation, all nodes in the first area 101 and the second area 102 can participate in a predefined flexible algorithm. Further, the first area 101 and the second area 102 can participate in the same predefined flexible algorithm. However, in another implementation, the nodes in the inter-area IGP network can participate in one or more different flexible algorithms.

[0081] In addition, the regional border nodes may use the TLV format defined above to announce the prefix SID, algorithm-specific metric, and algorithm ID of the destination node, as an extension of OSPFv2, OSPFv3, or ISIS according to the deployment scenario.

[0082] A second set of nodes participating in the same predefined flexible algorithm receives announcements from each of the two regional border nodes.

[0083] In step 302, a node in the second set of nodes from the second region 102, i.e., the source node, calculates each inter-area path metric associated with the path to the destination node via the corresponding regional border node, and each of the inter-area path metrics is based on the algorithm-specific metric announced by the corresponding regional border node. Here, the calculation of the path metric for reaching the destination node in another region via the corresponding regional border node includes the calculation of the link metric associated with one or more hops within the corresponding region. One or more of these hop points exist between the source node and other nodes from the second set of nodes to reach the corresponding regional border node in the second region 102. Further, in the first region, one or more hops may also exist between other nodes between the destination node and the corresponding regional border node. As an example, the link metric announced by the corresponding regional border node to the source node already includes the calculated link metric associated with one or more hops between the destination node from the first region and the corresponding regional border node.

[0084] In step 303, based on each calculated inter-area path metric, the source node determines the optimal path or the best path to reach the destination node via one of the two regional border nodes. The optimal path or the best path includes combining Figure 2 the selected regional border node discussed.

[0085] In step 304, the data packet is forwarded from the source node to the destination node via the determined path, i.e., via the selected regional border node.

[0086] The above solution enables each router in the second region 102 to calculate the inter-area path metric in the inter-area IGP network, so as to determine the best end-to-end path across regions through the SID algorithm-specific metric leaked by the regional border nodes.

[0087] Figure 4A Shows Figure 1Block diagram of nodes of the inter-area network 100 shown. The nodes may include a source node, which needs to determine an optimal end-to-end path across areas to a destination node in the inter-area network based on the SR-MPLS flexible algorithm process. In one implementation, the source node may be a router in the second area, and the destination node may be a router in the first area, and the area border node leaks information about the destination node in the first area to the second area. In another implementation, the source node may be a router in the first area, and the destination node may be a router in the second area, and the area border node leaks information about the destination node in the second area to the first area.

[0088] As Figure 4A shown, the source node 400A may include components disclosed herein to determine an optimal end-to-end path in the inter-area network 100 for forwarding a data packet to a destination node in the inter-area network 100. It should be understood that the source node 400A is located in an area (such as area 1) outside the area where the destination node is located (such as area 0). The source node 400A includes a receiving unit 401, a path metric calculation unit 402, a path determination unit 403, and a packet forwarding unit 404.

[0089] The receiving unit 401 is configured to receive an advertisement from each of at least two ABR nodes (such as Figure 1 the ABR RT 4 and ABR RT 5 shown), and an algorithm-specific metric associated with the destination node, where the destination node is from a first node set in the first area (such as area 0).

[0090] The path metric calculation unit 402 is configured to calculate each inter-area path metric associated with a path to the destination node via a corresponding area border node, and each inter-area path metric is based on the algorithm-specific metric advertised by the corresponding ABR node. As an example, the calculation of the path metric is similar to the calculation of the path metric for reaching RT 8 via each of ABR RT 4 and RT 5 implemented by RT 1 in the example described in conjunction with Figure 1 description.

[0091] The path determination unit 403 is configured to determine an optimal path or best path to the destination node via one of the at least two area border nodes based on the calculated each inter-area path metric. In the example described in conjunction with Figure 1 description, RT 1 selects RT 4 and determines the path via the selected ABR RT 4 as the optimal path to forward the data packet to RT 8 via ABR RT 4.

[0092] The packet forwarding unit 404 is used to forward the data packet from the source node to the destination node through the determined path.

[0093] The path determination unit 403 updates the labels in the MPLS forwarding table, and the packet forwarding unit 404 derives the corresponding labels of the nodes in the determined optimal path from the MPLS forwarding table.

[0094] The receiving unit 401, the path metric calculation unit 402, the path determination unit 403, and the packet forwarding unit 404 can be separate components, or an entire component including one or more other components with different implementations. In addition, one or more or all of these components can be based on hardware, such as integrated circuit components; or can be implemented as software implemented by the integrated processor of the node 400A; or can be a combination of hardware components and software as appropriate.

[0095] Figure 4B is shown Figure 1 A block diagram of the area border node 400B of the inter-area network 100 shown, the area border node can include Figure 1 Any one of the two area border nodes shown, that is, ABR RT 4 or ABR RT 5. The area border node can be the area border node selected by the source node, and through the area border node, the data packet can be forwarded to the destination node through the optimal path. According to an embodiment of the present invention, the source node, the destination node, and the area border node can all participate in the same flexible algorithm definition.

[0096] As Figure 4B shown, the area border node 400B can include the components disclosed herein to determine the optimal end-to-end path in the inter-area network 100 and forward the data packet from the source node of the inter-area network 100 to the destination node. It should be understood that the area border node 400B can include any one of at least two area border nodes existing between the first area and the second area. The area border node 400B includes a sending unit 405, a receiving unit 406, and a packet forwarding unit 407. According to an embodiment of the present invention, the area border node 400B is the selected ABR RT 4, as explained in conjunction with Figure 2 as explained.

[0097] The sending unit 405 is used to announce the algorithm-specific metric associated with the destination node in area 0 to the source node in area 1. The announced algorithm-specific metric can be received by the first node set in the second area, for example, received by the receiving unit 401 of the source node 400A, see Figure 4AAmong them, based on the algorithm-specific metrics advertised by the corresponding regional boundary nodes, the source node can calculate the inter-regional path metrics associated with the paths from the source node to ten destination nodes, and the paths include the corresponding regional boundary node 400B. For example, the calculation of the paths can be performed by the path metric calculation unit 402 of the source node, as Figure 4A shown.

[0098] It should be understood that the path calculation unit 402 of the source node calculates the inter-regional path metrics for the corresponding regional boundary node 400B, and also calculates each inter-regional path metric associated with the paths via at least one other regional boundary node. For example, the path metric calculation unit 402 calculates one inter-regional path metric based on the metrics advertised by ABR RT 4, and calculates one inter-regional path metric based on the metrics advertised by ABR RT 5.

[0099] If, after calculating the inter-regional path metrics of the corresponding regional boundary node 400B and other regional boundary nodes, the path via the regional boundary node 400B is determined to be the optimal path, the source node can select the path via the regional boundary node 400B to forward the data packet to the destination node in another region.

[0100] The receiving unit 406 is configured to: when the source node determines that the path associated with the metrics advertised by the regional boundary node 400B is the optimal path, receive the packet to be forwarded to the destination node via the path from the source node.

[0101] The packet forwarding unit 407 is configured to forward the data packet to the destination node through the determined path.

[0102] The sending unit 405, the receiving unit 406, and the packet forwarding unit 407 can be separate components, or can be an entire component including one or more other components with different implementations. In addition, one or more or all of these components can be based on hardware, such as integrated circuit components; or can be implemented as software implemented by the integrated processor of the node 400B; or can be a combination of hardware components and software as appropriate.

[0103] Figure 4C shows Figure 1 a block diagram of the system 400C in the inter-regional network 100 shown. The system facilitates determining the best end-to-end path to the cross-regional node in the inter-regional network based on the SR-MPLS flexible algorithm process. The system 400C includes a source node 400A-2 and a destination node 400A-1. In one embodiment, the source node 400A-2 and the destination node 400A-1 include Figure 4AComponents of the source node 400A shown in the figure, where A-2 represents the second region and A-1 represents the first region. As an example, in combination with Figure 1 , the source node 400A-2 is RT 1 and the destination node 400A-1 is RT 8.

[0104] Furthermore, the system 400C includes the regional border nodes 400B-1 and 400B-2. As explained in the present invention, the number of regional border nodes can be at least two. On the path determined by the source node 400A-2, one of the two regional border nodes is selected to forward the message to the destination node 400A-1. In one embodiment, the regional border nodes 400B-1 and 400B-2 include the components of the regional border node 400B shown in Figure 4B . As an example, in combination with Figure 1 , Figure 4C the represented regional border node includes the ABR RT 4 and ABR RT 5 shown in Figure 1 . When the source node 400A-2 determines the path via ABR RT 4 as the optimal path to forward the message to the destination node 400A-1, ABR RT 4 represents the regional border node that forwards the message to the destination node 400A-1.

[0105] In one implementation, the source node can be a router in the second region, the destination node can be a router in the first region, and the regional border node leaks the information of the destination node in the first region to the second region. In another implementation, the source node can be a router in the first region, the destination node can be a router in the second region, and the regional border node leaks the information of the destination node in the second region to the first region.

[0106] ​ shows additional and / or alternative components of the node 500 participating in the above inter-region IGP network 100. The node 500 includes a first set of nodes in the first region, a second set of nodes in the second region, and ABR nodes constituting a part of the first region and the second region.

[0107] The node 500 can be implemented on any general network component, such as a computer or network component with sufficient processing power, memory resources, and network throughput capacity to handle the necessary workload imposed thereon. The node 500 can at least include ​ the routers of region 0 and region 1 described.

[0108] ​A typical router for implementing one or more embodiments of the components disclosed herein is shown. Node 500 includes a processor 502 (which may be referred to as a central processing unit or CPU), which communicates with a storage device that includes auxiliary memory 504, read-only memory (ROM) 505, random access memory (RAM) 506, input / output (I / O) device 501, and network connection device 503. Processor 502 may be implemented as one or more CPU chips, or may be part of one or more application-specific integrated circuits (ASICs).

[0109] According to an embodiment of the present invention, processor 502 may include one or more components, such as ​ the path metric calculation unit 402, path determination unit 403, and packet forwarding unit 404 of the source node 400A described in

[0110] According to an embodiment of the present invention, input / output device 501 may include ​ the receiving unit 401 of the source node 400A shown. In other embodiments, input / output device 501 may include a transmission unit or transceiver for communicating with other nodes in the IGP network 100. The transmission unit or transceiver may be used to forward data packets and prefix SIDs to other nodes in the IGP network. In the case of using a transceiver, the transceiver may be used to receive prefix SIDs leaked by other nodes or ABRs and data packets forwarded from other nodes in the IGP network.

[0111] Auxiliary memory 504 generally includes one or more disk drives or tape drives for non-volatile storage of data, and serves as an overflow data storage device if the capacity of RAM 506 is not sufficient to store all working data. Auxiliary memory 504 may be used to store programs that will be loaded into RAM 506 when selected for execution. ROM 505 may be used to store instructions read during program execution and possibly data. ROM 505 is a non-volatile memory device, and its memory capacity is generally smaller than the large memory capacity of auxiliary memory 504. RAM 506 is used to store volatile data or may also be used to store instructions. The access speeds of ROM 505 and RAM 506 are generally faster than that of auxiliary memory 504.

[0112] Although several embodiments have been provided in the present invention, it should be understood that the systems and methods disclosed in the present invention may be embodied in many other specific forms without departing from the spirit or scope of the present invention. The examples of the present invention should be considered illustrative rather than restrictive, and the present invention is not limited to the details given in this text. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0113] In addition, without departing from the scope of the present invention, the technologies, systems, subsystems, and methods described and illustrated as discrete or separate in various embodiments may be combined or integrated with other systems, modules, technologies, or methods. Other items shown or discussed as being coupled or directly coupled or communicating with each other may also be indirectly coupled or communicating via some interface, device, or intermediate component in an electrical, mechanical, or other manner.

[0114] In the several embodiments provided in this application, it should be understood that the disclosed systems and methods may be implemented in other ways. For example, the described device embodiments are merely exemplary. For example, the unit division is only a logical function division and may be other divisions in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented. Additionally, the mutual coupling or direct coupling or communication connection shown or discussed may be achieved through some interfaces. The direct coupling or communication connection between devices or units may be achieved in an electronic, mechanical, or other form.

Claims

1. A method for performing optimal routing in an inter-regional Interior Gateway Protocol (IGP) network, characterized in that: The inter-area IGP network includes a first area and a second area, and the method includes: The area border node generates an IGP advertisement message, the IGP advertisement message including a Flex-Algo specific metric, wherein the Flex-Algo specific metric is a metric associated with a prefix of a destination node within the first area, the prefix of the destination node being from the first area; The area border node sends the IGP advertisement message within the second area, the first area includes the area border node, and the second area includes the area border node, wherein the Flex-Algo specific metric is used to calculate an end-to-end optimal path between the second area and the first area for the prefix of the destination node.

2. The method according to claim 1, characterized in that The IGP notification message also includes a Flex-Algo identifier.

3. The method according to claim 1 or 2, characterized in that The IGP advertisement message further includes a prefix segment identifier SID.

4. The method according to any one of claims 1 to 3, characterized in that The IGP advertisement message includes a type-length-value TLV, wherein the TLV is a sub-TLV of an Open Shortest Path First (OSPF) extended prefix TLV or a sub-TLV of an OSPFv3 E-Inter-Area-Prefix-LSA-TLV.

5. The method according to any one of claims 1 to 3, characterized in that The IGP notification message includes a TLV, where the TLV is a sub-TLV of any of the following intermediate system to intermediate system ISIS TLVs: - Extended IPv4 Reachability - TLV-135; -Multi-topology IPv4 reachability-TLV-235; -Extended IPv6 Reachability-TLV-236; - Multi-topology IPv6 reachability - TLV-237.

6. The method according to any one of claims 1 to 5, characterized in that Flex-Algo specific metrics are determined based on at least one of the following characteristics: IGP cost, latency, or exclusion of certain link attributes.

7. The method according to any one of claims 1 to 6, characterized in that The Flex-Algo specific metric is used to calculate the end-to-end optimal path between the second area and the first area for the prefix of the destination node, including: The Flex-Algo specific metric is used to calculate an inter-area path metric between the second area and the first area via the area boundary nodes, and the inter-area path metric is used to determine the end-to-end optimal path.

8. A method for performing optimal routing in an inter-regional Interior Gateway Protocol (IGP) network, characterized in that: The inter-area IGP network includes a first area and a second area, and the method includes: The source node receives a first IGP advertisement message sent by a first area border node, where the first IGP advertisement message includes a first flexible algorithm (Flex-Algo) specific metric, where the first Flex-Algo specific metric is a metric associated with a prefix of a destination node within the first area, where the prefix of the destination node is from the first area, the source node is from the second area, the first area includes the first area border node, and the second area also includes the first area border node. The source node receives a second IGP advertisement message sent by a second area border node, where the second IGP advertisement message includes a second Flex-Algo specific metric, where the second Flex-Algo specific metric is a metric associated with a prefix of the destination node within the first area, wherein the first area includes the second area border node, and the second area also includes the second area border node. The source node calculates an end-to-end optimal path between the second area and the first area for the prefix of the destination node according to the first Flex-Algo specific metric and the second Flex-Algo specific metric.

9. The method according to claim 8, characterized in that The first IGP advertisement message further includes a first Flex-Algo identifier, and the second IGP advertisement message includes a second Flex-Algo identifier.

10. The method according to claim 8 or 9, characterized in that The first IGP advertisement message further includes a first prefix segment identifier (SID), and the second IGP advertisement message further includes a second prefix SID.

11. The method according to any one of claims 8 to 10, characterized in that The first IGP advertisement message includes a type-length-value TLV, wherein the TLV is a sub-TLV of an Open Shortest Path First (OSPF) extended prefix TLV, or a sub-TLV of an OSPFv3E-Inter-Area-Prefix-LSA-TLV.

12. The method according to any one of claims 8 to 10, characterized in that The first IGP advertisement message includes a TLV, where the TLV is a sub-TLV of any of the following intermediate system to intermediate system ISIS TLVs: - Extended IPv4 Reachability - TLV-135; -Multi-topology IPv4 reachability-TLV-235; -Extended IPv6 Reachability-TLV-236; - Multi-topology IPv6 reachability - TLV-237.

13. The method according to any one of claims 8 to 12, characterized in that The first Flex-Algo specific metric is determined based on at least one of the following characteristics: IGP cost, latency, or exclusion of certain link attributes.

14. The method according to any one of claims 8 to 13, characterized in that The source node calculates, for the prefix of the destination node, an end-to-end optimal path between the second area and the first area according to the first Flex-Algo specific metric and the second Flex-Algo specific metric, including: The source node calculates, based on the first Flex-Algo specific metric, a first inter-area path metric between the second area and the first area via a boundary node of the first area; The source node calculates, based on the second Flex-Algo specific metric, a second inter-area path metric between the second area and the first area via a boundary node of the second area; The source node determines the end-to-end optimal path according to the first inter-area path metric and the second inter-area path metric.

15. A network device, characterized in that: The network device serves as a regional border node in an inter-region Interior Gateway Protocol (IGP) network, and the network device executes the method according to any one of claims 1 to 7.

16. A network device, characterized in that: The network device serves as a source node in an inter-region Interior Gateway Protocol (IGP) network, and the network device executes the method according to any one of claims 8 to 14.

17. A system for performing optimal routing in an inter-regional Interior Gateway Protocol (IGP) network, characterized in that: The system includes a source node and an area boundary node, wherein the area boundary node is the network device according to claim 15, and the source node is the network device according to claim 16.

18. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer program code. When the computer program code is executed by a communication device, the communication device performs the method according to any one of claims 1 to 14.

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