The invention relates to computer networks and, more particularly, to engineering traffic flows within computer networks.
Routing devices within a network, often referred to as routers, maintain routing information that describe available routes through the network. Upon receiving an incoming packet, the router examines information within the packet and forwards the packet in accordance with the routing information. In order to maintain an accurate representation of the network, routers exchange routing information in accordance with one or more defined routing protocol, such as the Border Gateway Protocol (BGP).
The term “link” is often used to refer to the connection between two devices on a network. The link may be a physical medium, such as a copper wire, a coaxial cable, any of a host of different fiber optic lines or a wireless connection. In addition, network devices may define “virtual” or “logical” links, and map the virtual links to the physical links. As networks grow in size and complexity, the traffic on any given link, including peering links, may approach a maximum bandwidth capacity for the link, thereby leading to congestion and loss.
Multi-Protocol Label Switching (MPLS) is a mechanism used to engineer traffic patterns within Internet Protocol (IP) networks. By utilizing MPLS, a source device can request a path through a network to a destination device, i.e., a Label Switched Path (LSP). An LSP defines a distinct path through the network to carry MPLS packets from the source device to a destination device. Each router along a LSP allocates a label and propagates the label to the closest upstream router along the path. Routers along the path cooperatively perform MPLS operations to forward the MPLS packets along the established path. In order to carry multicast packets, a source device can request a path through a network to multiple destination devices, i.e., a Point to Multi-Point (P2MP) LSP.
In the case of a P2MP LSP, one or more of the routers along the path may comprise branch routers located at points where the path divides. In addition to performing MPLS operations to forward the MPLS multicast packets along the path, the branch routers perform replication of the multicast packets such that each branch of the P2MP LSP continues to carry copies of the multicast packets. A variety of protocols exist for establishing LSPs. For example, the Label Distribution Protocol (LDP), and the Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE).
In general, the invention is directed toward techniques for Multi-Protocol Label Switching (MPLS) upstream label assignment for the Resource Reservation Protocol with Traffic Engineering (RSVP-TE). The techniques include extensions to the RSVP-TE that enable distribution of upstream assigned labels in Path messages from an upstream router to two or more downstream routers of tunnel established over a network. The tunnel may comprise a RSVP-TE P2MP Label Switched Path (LSP) or an Internet Protocol (IP) multicast tunnel.
The techniques also include extensions to the RSVP-TE that enable a router to advertise upstream label assignment capability to neighboring routers in the network. The MPLS upstream label assignment using RSVP-TE described herein enables a branch router to avoid traffic replication on a Local Area Network (LAN) for RSVP-TE P2MP LSPs.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Upstream router 20 and downstream routers 22 and 24 maintain routing information that describes available routes through computer network 12. Upon receiving an incoming packet, the routers examine information within the packet and forward the packet in accordance with the routing information. In order to maintain an accurate representation of network 12, the routers exchange routing information, e.g., bandwidth availability of links, in accordance with a defined routing protocol, such as an Interior Gateway Protocol (IGP).
In the example of
The extensions to the RSVP-TE enable routers 20, 22 and 24 to advertise upstream label assignment capability to neighboring routers in network 12. The extensions to RSVP-TE also enable upstream router 20 to distribute upstream assigned labels in Path messages to downstream routers 22 and 24 upon receiving advertisements indicating upstream label assignment capability from downstream routers 22 and 24. In the case where tunnel 18 comprises a RSVP-TE P2MP LSP, upstream label assignment described herein enables a branch router, such as router 20, to avoid replicating traffic to routers 22 and 24 on a Local Area Network (LAN).
In some cases, subscriber devices within subscriber networks 14 request multicast streams, such as IPTV channels, from source network 10. RSVP-TE with upstream label assignment extensions enables transmission of multicast traffic over tunnel 18 from source network 10 to subscriber networks 18 without requiring upstream router 20 to perform traffic replication. For example, upstream router 20 may allocate the same upstream assigned label to downstream router 22 and downstream router 24 such that upstream router 20 may forward traffic from source network 10 in a single packet with the upstream assigned label to both routers 22 and 24.
In accordance with principles of the invention, RSVP-TE is extended to include upstream label assignment capability and upstream assigned label distribution. RSVP-TE may also include a tunnel identifier that identifies tunnel 18, e.g., RSVP-TE P2MP LSP or IP multicast tunnel, as carrying upstream label assignments and traffic from upstream router 20 to downstream routers 22 and 24. In this way, the techniques enabling binding of the upstream assigned label to the tunnel 18. For example, RSVP-TE associates a forwarding equivalence class (FEC) with each LSP in network 12. In the case where tunnel 18 comprises a RSVP-TE P2MP LSP, upstream router 20 with upstream label assignment capability binds an upstream assigned label to the FEC for tunnel 18.
As described in more detail below, the RSVP-TE tunnel identifier also enables RSVP-TE P2MP hierarchy. Hierarchy is needed when an “inner” RSVP P2MP LSP is established over multiple edge domains via an “outer” RSVP P2MP LSP established within a backbone domain. The upstream label assignment extensions to RSVP-TE allow an upstream router within the backbone domain to tunnel the inner P2MP LSP with upstream assigned labels over the outer P2MP LSP within the backbone domain that has downstream assigned labels. The tunnel identifier allows the upstream router to signal upstream assigned labels for the inner P2MP LSP with a tunnel identifier for the outer P2MP LSP to the downstream routers of the outer P2MP LSP. In this way, the upstream router effectively binds the inner P2MP LSP to the outer P2MP LSP.
An exemplary application of RSVP-TE with upstream label assignment extensions will be described in which network 12 comprises a LAN and tunnel 18 within network 12 comprises a RSVP-TE P2MP LSP. Conventionally, RSVP-TE P2MP LSPs on a LAN require “ingress replication” in which a branch router for the P2MP LSP on the LAN replicates a received packet and sends a separate copy of the packet on the P2MP LSP to each of the downstream routers on the LAN that are adjacent to the branch router. In order to increase efficiency of bandwidth utilization, it is desirable for the branch router of the P2MP LSP on the LAN to send a single copy of the packet to multiple downstream routers that are adjacent to the branch router of the P2MP LSP.
As illustrated in
Downstream routers 22 and 24 “reserve” the upstream assigned label in a separate context specific upstream label space maintained for upstream router 20. Upstream router 20 can then transmit a single packet for the P2MP LSP to downstream routers 22 and 24 with the upstream assigned label L. In the case where tunnel 18 includes a plurality of downstream routers (not shown), if a subset of the downstream routers do not support upstream label assignment, upstream router 20 may still use upstream label assignment for the remaining sub-set of the downstream routers. Upstream router 20 will then use ingress replication and downstream label assignment for downstream routers that do not support upstream label assignment.
In the example illustrated in
Control unit 36 maintains routing information 44 that describes the topology of a network and, in particular, routes through the network. Routing information 44 may include, for example, route data that describes various routes within the network, and corresponding next hop data indicating appropriate neighboring devices within the network for each of the routes. Router 30 updates routing information 44 to accurately reflect the topology of the network.
Control unit 36 also maintains forwarding information 46 that associates network destinations with specific next hops and corresponding interface ports. In general, when router 30 receives a multicast packet with a downstream assigned label via one of inbound links 33, control unit 36 determines a destination and associated next hop for the packet in accordance with routing information 44 and forwards the packet on one of outbound links 34 to the corresponding next hop in accordance with forwarding information 46 based on the destination of the packet.
In accordance with the invention, control unit 36 provides an operating environment for RSVP-TE 38 to execute. RSVP-TE 38 includes an upstream capability module 40 and an upstream label module 42 to support upstream assigned labels. Control unit 36 also maintains upstream label spaces 48 for each upstream router. Upon receiving an upstream assigned label from an upstream router, router 30 reserves the label in a context specific label space within upstream label spaces 48 for that upstream router. Upstream label spaces 48 include forwarding information for each upstream router that associates network destinations with specific next hops and corresponding interface ports. When router 30 receives a multicast packet from an upstream router with an upstream assigned label via one of inbound links 33, control unit 36 determines a destination and associated next hop for the packet in accordance with routing information 44 and forwards the packet on one of outbound links 34 to the corresponding next hop in accordance with forwarding information for that upstream router within upstream label spaces 48 based on the destination of the packet.
In the case where router 30 comprises an upstream router or root of a tunnel, router 30 establishes the tunnel across a network having two or more downstream routers or leaves. Upstream capability module 40 then sends advertisements to neighboring routers in the network indicating that router 30 is capable of supporting upstream assigned labels. In addition, upstream capability module 40 receives advertisements from the neighboring routers in the network indicating that at least some of neighboring routers are capable of supporting upstream assigned labels.
Upon receiving the advertisements, upstream label module 42 allocates an upstream assigned label in a Path message to each of the downstream routers of the tunnel indicated to be capable of supporting upstream assigned labels. Upstream label module 42 then receives Resv messages from the capable downstream routers that do not include labels. Router 30 uses the upstream assigned label to forward packets to the downstream routers capable of supporting upstream assigned labels. In addition, control unit 36 may receive downstream assigned labels in Resv messages from downstream routers of the tunnel that do not support upstream assigned labels. In that case, router 30 uses the downstream assigned labels to forward packet to the downstream routers that are not capable of supporting upstream assigned labels.
Upstream label module 42 may also send a tunnel identifier in the Path message to each of the downstream routers of the tunnel that identifies the tunnel as carrying upstream assigned labels and packets from router 30. In this way, the tunnel identifier enables binding of the upstream label to the tunnel. In the case of P2MP LSP hierarchy, upstream label module may send an upstream assigned label for an “inner” P2MP LSP to downstream routers of an “outer” P2MP LSP that identify the “outer” P2MP LSP. In this way, the tunnel identifier enables binding of the inner P2MP LSP to the outer P2MP LSP.
In the case where router 30 comprises a downstream router or leaf of a tunnel, upstream capability module 40 sends advertisements to neighboring routers in the network indicating that router 30 is capable of supporting upstream assigned labels. Upstream label module 42 receives an upstream assigned label in a Path message from the upstream router or root of the tunnel. Router 30 reserves the label in a context specific label space within upstream label spaces 48 for that upstream router.
Upstream label module 42 then sends a Resv message that does not include labels to the upstream router. Upstream label module 42 recognizes that an upstream assigned label was received from the upstream router, and knows not to send a downstream assigned label back to the upstream router. Upstream label module 42 may also receive a tunnel identifier in the Path message from the upstream router of the tunnel that identifies the tunnel as carrying upstream assigned labels and packets from the upstream router. Router 30 receives packets from the upstream router with the upstream assigned label.
The architecture of router 30 illustrated in
Control unit 36 may be implemented solely in software, or hardware, or may be implemented as a combination of software, hardware, or firmware. For example, control unit 36 may include one or more processors which execute software instructions. In that case, the various software modules of control unit 36 may comprise executable instructions stored on a computer-readable medium, such as computer memory or hard disk.
The usage of RSVP-TE Hello messages for exchanging upstream label assignment capability implies that a router may exchange RSVP-TE Hellos with a neighboring router before sending or receiving any other RSVP-TE messages with that neighboring router. An upstream router cannot allocate upstream assigned labels to downstream routers of a tunnel unless the upstream router knows that at least some of the downstream routers support upstream assigned labels. U flag 52 within Capability object 50 provides a mechanism for routers to advertise upstream label assignment capability to neighboring routers in a network.
The upstream label assignment capable U flag 52 comprises 1 bit. When U flag 52 is set (U=1), the router is capable of both distributing upstream assigned labels and receiving upstream assigned labels. When U flag 52 is not set (U=0), the router is not capable of either distributing or receiving upstream assigned labels. The reserved bits are be set to zero on transmission and ignored on receipt.
An upstream router or root of a RSVP-TE tunnel assigns upstream assigned labels, and distributes the upstream assigned labels to downstream router of the RSVP-TE tunnel within RSVP-TE Path messages. The upstream router does not distribute the UPSTREAM_ASSIGNED_LABEL object 54 to a downstream router of the tunnel if the downstream router did not advertise the Capability object 50 with the U flag 52 (from
If a downstream RSVP-TE router of the tunnel receives a Path message that carries UPSTREAM_ASSIGNED_LABEL object 54 and the downstream router does not support the object class-number and class-type, the downstream router will return an “Unknown Object C-Num/C-Type” error to the upstream router in a Resv message. If the downstream router does support the UPSTREAM_ASSIGNED_LABEL object 54, but is unable to process the upstream assigned label, the downstream router may send a PathErr with the error code “Routing problem” and the error value “MPLS Upstream Assigned Label Processing Failure” to the upstream router in a Resv message.
If the downstream router of the tunnel successfully processes the Path message and the upstream assigned label, the downstream router sends a Resv message to the upstream router, but does not include a downstream assigned label in the Resv Message. An upstream router and a downstream router for a P2MP LSP with an associated FEC F, either use downstream assigned label distribution or upstream assigned label distribution for FEC F, but not both, for packets transmitted on the P2MP LSP from the upstream router to the downstream router.
When using RSVP-TE for upstream label assignment, the IF_ID RSVP_HOP object may be used to signal the Tunnel Identifier. If the upstream router uses an IP or MPLS tunnel to transmit MPLS packets with upstream assigned labels to the downstream router, the upstream router includes the IF_ID RSVP_HOP object in Path messages along with the UPSTREAM_ASSIGNED_LABEL object 54 from
This mechanism enables RSVP-TE P2MP hierarchy. The Tunnel Identifier allows an upstream router to tunnel an “inner” P2MP LSP, the label for which is upstream assigned, over an “outer” P2MP LSP that has multiple downstream routers. The RSVP-TE P2MP LSP TLV allows the upstream router to signal the binding of the inner P2MP LSP to the outer P2MP LSP to the multiple downstream routers. The control plane signaling between the upstream router and the multiple downstream routers for the inner P2MP LSP uses directed RSVP-TE signaling messages.
Upstream capability module 40 advertises upstream label assignment capability to neighboring routers in the network (72). The advertisements may comprise RSVP Hello messages including a Capability object with a set U flag. In turn, upstream capability module 40 may receive advertisements indicating upstream label assignment capability from the neighboring routers in the network (74).
For purposes of explanation, it is assumed that at least two of the downstream routers advertise that they are capable of supporting upstream label assignment. Upstream label module 42 then allocates an upstream assigned label to the capable downstream routers of the tunnel in a Path message (76). The label allocation may comprise an UPSTREAM_ASSIGNED_LABEL object. Upstream label module 42 may also send a tunnel identifier in the Path message to the capable downstream routers that identifies the tunnel as carrying upstream assigned labels from upstream router 30. The tunnel identifier may comprise TLVs of an RSVP-TE object that signal either a RSVP-TE P2MP LSP or an IP Multicast Tunnel. In this way, upstream router 30 binds the upstream assigned label to the tunnel with the tunnel identifier (78).
Upstream router 30 then forwards a single packet received from source network 10 to the capable downstream routers of the tunnel with the upstream assigned label (80). Upstream router 30 may also send packets to downstream routers of the tunnel that are not capable of supporting upstream assigned labels. In this case, upstream router 30 receives downstream assigned labels from each of the incapable downstream router of the tunnel. Upstream router 30 then performs ingress replication and sends copies of the packets to each of the incapable downstream routers with the associated downstream assigned label.
As described above, the RSVP-TE tunnel identifier enables RSVP-TE P2MP hierarchy. First P2MP LSP 90 within backbone domain 82 comprises an “outer” P2MP LSP, and second P2MP LSP 98 across edge domains 84, 86 and 88 comprises an “inner” P2MP LSP. The upstream label assignment extensions to RSVP-TE described herein allow UR 92 within backbone domain 82 to tunnel second P2MP LSP 98 with upstream assigned labels over first P2MP LSP 90 within backbone domain 82. The tunnel identifier described herein allows UR 92 to signal upstream assigned labels for second P2MP LSP 98 with an identifier for first P2MP LSP 90 to DRs 94 and 96 of first P2MP LSP 90. In this way, UR 92 effectively binds second P2MP LSP 98 to first P2MP LSP 90.
RSVP-TE P2MP hierarchy allows all of the routers within backbone domain 82 to maintain control and forwarding state only for first P2MP LSP 90 within backbone domain 82. The control and forward state for second P2MP LSP 98 is nested within first P2MP LSP 90. Therefore, only the routers within backbone domain 82 associated with first P2MP LSP 90 (i.e., UR 92, DR 94, and DR 96) maintain the control and forwarding state for second P2MP LSP 98.
For purposes of explanation, it is assumed that DRs 94 and 96 within backbone domain 82 advertise that they are capable of supporting upstream label assignment to UR 92. UR 92 then allocates an upstream assigned label for second P2MP LSP 98 in a Path message to DRs 94 and 96 within the backbone domain 82 (114). UR 92 also sends a tunnel identifier in the Path message to DRs 94 and 96 within backbone domain 82 that identifies first P2MP LSP 90. In this way, UR 92 binds second P2MP LSP 98 to first P2MP LSP 90 with the tunnel identifier (116).
UR 92 and all the routers within backbone domain 82 maintain control and forwarding state for first P2MP LSP 90 within backbone domain 82. The control and forward state for second P2MP LSP 98 is nested within first P2MP LSP 90. Therefore, only UR 92, DR 94, and DR 96 of first P2MP LSP 90 within backbone domain 82 maintain the control and forwarding state for second P2MP LSP 98. UR 92 then encapsulates a single packet received on second P2MP LSP 98 in first P2MP LSP 90 (122) and forwards the single packet to DRs 94 and 96 of first P2MP LSP 90 within backbone domain 82 with the upstream assigned label (124).
Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.
This application is a continuation of application Ser. No. 11/508,096, filed Aug. 22, 2006, now U.S. Pat. No. 7,787,380, which claims the benefit of U.S. Provisional Application No. 60/817,851, filed Jun. 30, 2006, the entire content of each being incorporated herein by reference.
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Number | Date | Country | |
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60817851 | Jun 2006 | US |
Number | Date | Country | |
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Parent | 11508096 | Aug 2006 | US |
Child | 12871784 | US |