| Network Working Group | J.M. Jeganathan |
| Internet-Draft | H. Gredler |
| Intended status: Standards Track | Y. Shen |
| Juniper Networks | |
| Oct 12, 2012 |
RSVP-TE LSP egress fast-protection-00
draft-minto-rsvp-lsp-egress-fast-protection-00
RFC4090 defines an RSVP fast reroute mechanism for local repairing LSP tunnel in the order of 10s milliseconds, in the event of a downstream link or node failure. However, the mechanism does not provide node protection for LSP egress nodes. This document describes two methods to establish a bypass LSP from the penultimate-hop node of an LSP to a backup egress node, which could be used to protect the LSP against egress node failure. The methods enable local repair in the order of 10s of millisecond, in the event of the egress node failure. These methods are only applicable if traffic carried by the LSP could be rerouted to ultimate destination by the backup egress node.
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This document define two methods that could enable fast protection for egress node failure for RSVP-TE signaled LSP tunnels. Both methods have a common concept of primary egress node and backup egress node for a tunnel endpoint address. The methods differ by how tunnel endpoints are modeled in the network. The primary egress node of an LSP (called protected LSP) terminates the LSP in steady state, while a bypass LSP is established from the penultimate-hop node to the backup egress node. The penultimate-hop node, serving as a PLR (point of local repair), redirects traffic to the backup egress node of the LSP via the bypass LSP in the event of primary egress node failure, and the backup egress node forwards the traffic to the ultimate destination. How the backup egress node forwards traffic is beyond the scope this document. For one example, the backup egress node could mirror from the primary egress node the inner labels (e.g. layer-2/3 VPN service labels) carried by the traffic, and forward the traffic based on those labels by using the mechanisms specified in [pwe3-endpoint-fast-protection] and [l3vpn-egress PE-fast-protection].
[R1] [R8]
\ /
[R2]---[R3]----[R4]-----[R5]---[R6]
\ / \\
[R9]-----[R10] [R7]
Protected LSP to-R6.x: [R1->R3->R4->R5->R6.x]
Protected LSP to-R6.y: [R1->R3->R4->R5->R6.y]
Protected LSP to-sec-R6.x: [R1->R3->R9->R10->R5->R6.x]
Protected LSP to-R8.z: [R2->R3->R4->R5->R8.z]
Egress-Bypass LSP Tunnel by-R7.x: [R5->R7.x]
Egress-Bypass LSP Tunnel by-R7.y: [R5->R7.y]
Egress-Bypass LSP Tunnel by-R7.z: [R5->R7.z]
x, y, z: Tunnel destination addresses.
R6 has x,y destination addresses.
Figure 1
In Figure 1, 4 LSPs are required egress protection. R6 and R8 are the primary egresses for 4 LSPs, R7 is backup egress and R5 is penultimate hop node for all LSPs. R5 establish bypass LSP to R7 for fast protection to handle the R6 or R8 failure. Below table shows the protected LSP and bypass LSP in R5.
| Protected LSP | Egress Bypass LSP |
|---|---|
| to-R6.x | by-R7.x |
| to-R6.y | by-R7.y |
| to-sec-R6.x | by-R7.x |
| to-R8.z | by-R7.z |
Two methods defined in the documents that enable the backup LSP to establish to backup egress.
In the proxy method, an LSP endpoint address is represent as a virtual node in the TE domain attached to the primary egress node and the backup egress node via bidirectional point-to-point TE links. With this representation, the penultimate-hop node of the LSP could use the normal procedure of RSVP fast-reroute PLR to set up a bypass LSP to the backup egress node, by avoiding the primary egress node. This methed has the advantage of not requiring software upgrade on the penultimate-hop node, and thus can ease the deployment this technology.
[R1] [R8]
\ /
[R2]---[R3]----[R4]-----[R5]---[R6]---[x]
\ / \ /
[R9]-----[R10] [R7]---+
x: Tunnel destination addresses in proxy method.
With proxy method, topology is modeled as figure 2 in the rest of the network for LSP destination address x which required egress protection and R6 is primary R7 is backup.
In alias method, an LSP endpoint address is associated with an dedicated IP address on the backup egress node. This IP address is called an alias. The penultimate-hop node of the LSP may learn the alias via IGP or configuration, and use it as the destination when computing a path for the bypass LSP. With this method, the penultimate-hop node can set up a bypass LSP to the backup egress node, by avoiding the primary egress node. This method requires software upgrade penultimate-hop node, but is flexile to support all traffic engineering constraints.
[R1] [R8]
\ /
[R2]---[R3]----[R4]-----[R5]---[R6]x
\ / \
[R9]-----[R10] [R7](x)
x: Tunnel destination addresses in alias method.
In figure 3, let say x is tunnel destination address and R6 is primary and R7 is backup then with alias method, R6 advertises x as secondary loopback address and R5 knows x has backup either by configuration or R7 advertisement in IGP.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
PLR: Point of Local Repair. The head-end LSR of a backup tunnel or a detour LSP
PHN: Penultimate Hop Node for an LSP.
Primary egress node: Node terminates a LSP in steady state.
Primary: Primary egress node.
Egress Protected LSP: A Protected LSP that also required protection from primary egress node failure
Backup egress node: Node could rerouted/repaired data carried in a protected LSP
Backup node: Backup egress node.
Protector: Backup egress node.
Protector and Backup node are used interchangeably but convey the same meaning.
In this method, an LSP endpoint address is represented as a virtual TE node connected to a primary egress node and a backup egress node with bidirectional TE links, as shown figure 1. With this model, node protection establishment and bypass LSP path computation on the penultimate hop of an LSP can follow the procedure described in RFC4090.
primary egress -
\ metric 1, TE metric 1, bandwidth max
\
\
\
\ metric max, TE metric max, bandwidth 0
|
proxy node [stub node]
|
/ metric max, TE metric max, bandwidth 0
/
/
/
/ metric max, TE metric max, bandwidth 0
backup egress-
Figure 4
Tunnel destination advertised as stub proxy TE node required two parts. A node representation (proxy-node) and links to and from primary egress and backup egress..
Only zeroth fragment of the proxy-node is only valid. All Other fragments SHOULD be ignored. Zeroth fragment MUST include area address TLV and MAY include hostname TLV.
The set of area addresses advertised MUST be a subset of the set of Area Addresses advertised in the protected LSP number zero at the corresponding level. Preferably, the advertisement SHOULD be syntactically identical to that included in the normal LSP number zero at the corresponding level. The hostname could be set as <tunnel-destination + protected hostname>.
The Overload (OL) MUST be set to 1. The Attached (ATT), and Partition Repair (P) bits MUST be set to 0.
The advertising router and Link State ID of router LSA be LSP end point address. All options bits in router LSA MUST be set to zero. The number of links MUST be 2
The ingress node of an LSP should follow same procedure in RFC 2205 and RFC 4090 to signal the LSP. In particular, it should set the destination to the endpoint address (i.e. the proxy node), and the "link protection desired" flag and the "node protection desired" flag in SESSION_ATTRIBUTE of Path message. In path computation, it MAY optionally set not to use MAX metric link, as another constraint, to avoid the link between the backup egress and the proxy node.
When the primary egress node receives Path message for the LSP with destination matching the proxy node address, it MUST append two entities in the RRO object of Resv message, first for the proxy node as a virtual downstream node, and second for itself as virtual transit node. The entity for the proxy node is encoded as {proxy node address, proxy link ID, implicit NULL}.
When the penultimate hop node receives Resv message from primary egress, it sees itself as two hops away from LSP's destination rather than one hop, based on the RRO. Thus, it can set up node protection for the LSP by following the procedure described in RFC 4090. It SHOULD set up a bypass LSP to the backup egress node. When computing a path for bypass LSP, it SHOULD avoid the primary egress node and choose a path via the backup egress node to reach the proxy node.
The penultimate hop node SHOULD uses the same procedure as defined RFC4090 to signal the backup Path, in the event of failure of the primary egress node.
When the backup egress node receives the Path message of the bypass LSP, it MUST terminate the Path message based on the match bewteen the LSP destination and the proxy node address. It SHOULD assign a non-reserved label to the bypass LSP, and point the label to a specific label table where the labels learned from the primary egress node are installed. This can facilitate forwarding of traffic when the backup egress node receives traffic over the bypass LSP during local repair. In this case, the traffic will be carrying inner labels assigned by the primary egress node, and a further label lookup in the specific label table SHOULD enable the backup egress node to forward traffic to the ultimate destination.
During local repair, the backup egress node will receive Path message of backup LSP from the penultimate hop node. The backup egress node SHOULD terminate the Path message, and respond with a Resv message.
Pros
Cons
In this model Penultimate hop node understand tunnel end point has a backup egress which is may not protected LSP path and backup egress could repair traffic carried protected LSP in the event of primary egress failure. After primary egress failure PHN reroute using bypass tunnel to backup egress. The tunnel endpoint address and backup egress mapping could be configured in penultimate hop node or signaled through IGP from the backup. Following table illustrate the PNH mapping primary to backup mapping for the figure 1.
| Primary Egress Router ID | Backup egress router ID | Backup LSP destination address. |
|---|---|---|
| 10.1.2.6 | 10.1.1.6 | 10.1.1.7 |
| 10.1.2.6 | 10.1.3.6 | 10.1.1.6 |
| 10.1.1.7 | 10.1.3.6 | 10.1.2.8 |
| 10.1.1.8 | 10.1.1.7 | 10.1.2.8 |
Ingress should follow same procedure in RFC 3209 with tunnel endpoint address and path computation could use RFC 5786 advertised tunnel endpoint address.
Primary egress node advertises tunnel end points that required protection using RFC 5786 in OSPF and/or IP interface addresses TLV(132) in ISIS. These TLVs are defines as Local address advertisement in TE. And rest of behavior is same RFC 4090.
When backup receives a Path message not through a bypass tunnel for a destination address it protects with ERO constains only one self sub objects then it MUST accept and respond with RRO objects in Resv message. The RRO object {node ID, Ip address, label} for tunnel end address set with {Node ID, tunnel endpoint address, non-NULL}. This non-NULL will be used for identify LSP it protects in forwarding. Backup could also signals protection availability for tunnel end point addresses through IGP.
The Backup egress sends Resv, ResvTear, and PathErr messages by sending them directly to the address in the RSVP_HOP object, as specified in [RSVP-TE].
When backup receive Path message through a bypass tunnel with one sub-object for destination address it protects then it should accept ERO.
PLR learns/configured backup egress for tunnel a end point address advertised by primary egress. When PLR setup bypass for node protection LSP it will also lookup for the backup egress if PLR is penultimate hop of the LSP. If backup egress is available for LSP tunnel end point address then it setup bypass-LSP to backup egress if it is not setup already. The constrains will be exclude egress node. PNH could setup bypass-LSP with destination as backup egress node or tunnel endpoint address. If the bypass tunnel endpoint address is not the protected LSP tunnel endpoint then it also initiates backup LSP for tunnel end point address through bypass tunnel to learn the label to use in failure.
PHP SHALL uses the same procedure as defined RFC4090 to signal the backup Path.
PLR has to find the desired explicit route for the backup path. This can be done using a CSPF computation. If PLR is PNH for the protected LSP needs node protection then destination for backup path MUST be backup egress router ID with constrain that LSP cannot traverse the primary egress node and/or link whose failure is being protected against. For other constrains SHOULD follow RFC4090.
A PHN use one or more bypass tunnels to protect against the failure of a egress primary node. This bypass tunnels set up in advance or dynamically created as new protected LSPs are signaled.
To support facility backup, the PHN must determine the label that will indicate to the backup egress that packets received with that label should be processed by primary egress context. This can be done by explicitly signaling backup path before failure or setup the UHP bypass tunnel to backup egress with tunnel endpoint address as destination.
Sub-objects belonging to abstract nodes that precede the tunnel endpoint Point are removed. A sub-object identifying the Backup Tunnel destination is then added.
PHN SHALL uses the same procedure as defined RFC4090 during the local repair.
Pro
Cons
The security considerations discussed in RFC 5036, RFC 5331, RFC 3209, and RFC 4090 apply to this document.
This document leverages work done by Hannes Gredler, Yakov Rekhter and several others on LSP tail-end protection. Thanks to Nischal Sheth, Nitin Bahadur, Yimin shen, Ashwin Sampath and Kaliraj Vairavakkalai for their contribution.
| [RFC5286] | Atlas, A. and A. Zinin, "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, September 2008. |
| [RFC5714] | Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714, January 2010. |
| [pwe3-endpoint-fast-protection] | Shen, Y, Aggarwal, R, "PW Endpoint Fast Failure Protection", 2011. |
| [l3vpn-egress-PE-fast-protection] | Jeganathan, J and G Gredler, "2547 egress PE Fast Failure Protection", 2011. |