MPLS Traffic Engineering NANOG18 Robert Raszuk - IOS Engineering

MPLS Traffic Engineering NANOG18 Robert Raszuk - IOS Engineering raszuk@cisco.com

Location of files This presentation, handouts & demo are located at: ftp://ftpeng.cisco.com/rraszuk/nanog18 RR_MPLS_TE_Nanog.pdf - this presentation TE_Monitor.pdf - show & debug commands TE_Config.pdf - full configuration syntax TE_SampleCfg.pdf - configuration sample TE_DEMO.tar - Tared TE offline demo (HTML) TEisistdp_1.pdf - Demo’s Lab Topology Cost saving that results in more efficient use of bandwidth resources helps to reduce overall cost of operations. This, in turn, helps service providers to gain advantage over its competitors. And this advantage becomes more and more important as the Service Provider market gets more and more competitive. More efficient use of bandwidth resources means that a provider could avoid a situation where some parts of its network are congested, while other parts are underutilized.

Traffic Engineering: Motivations
Reduce the overall cost of operations by more efficient use of bandwidth resources by preventing a situation where some parts of a service provider network are over-utilized (congested), while other parts under-utilized Cost saving that results in more efficient use of bandwidth resources helps to reduce overall cost of operations. This, in turn, helps service providers to gain advantage over its competitors. And this advantage becomes more and more important as the Service Provider market gets more and more competitive. More efficient use of bandwidth resources means that a provider could avoid a situation where some parts of its network are congested, while other parts are underutilized. The ultimate goal is cost saving !

Traffic Engineering: Motivations
MPLS and Traffic Eng allows for one to spread the traffic and distribute it across the entire network infrastructure like magnetic fields between poles while also providing the redundancy required for high availability service. (Eric Dean) Cost saving that results in more efficient use of bandwidth resources helps to reduce overall cost of operations. This, in turn, helps service providers to gain advantage over its competitors. And this advantage becomes more and more important as the Service Provider market gets more and more competitive. More efficient use of bandwidth resources means that a provider could avoid a situation where some parts of its network are congested, while other parts are underutilized.

Without Traffic Engineering
Cars: SFO-LAX SAN-SMF LAX-SFO SMF-SAN No Traffic Engineering analogy to Human Drivers Cost saving that results in more efficient use of bandwidth resources helps to reduce overall cost of operations. This, in turn, helps service providers to gain advantage over its competitors. And this advantage becomes more and more important as the Service Provider market gets more and more competitive. More efficient use of bandwidth resources means that a provider could avoid a situation where some parts of its network are congested, while other parts are underutilized.

With Traffic Engineering
Cars: SFO-LAX SAN-SMF LAX-SFO SMF-SAN Traffic Engineering analogy to Auto Pilot Cost saving that results in more efficient use of bandwidth resources helps to reduce overall cost of operations. This, in turn, helps service providers to gain advantage over its competitors. And this advantage becomes more and more important as the Service Provider market gets more and more competitive. More efficient use of bandwidth resources means that a provider could avoid a situation where some parts of its network are congested, while other parts are underutilized.

Routing solution to Traffic Engineering
Construct routes for traffic streams within a service provider in such a way, as to avoids causing some parts of the provider’s network to be over-utilized, while others parts remain under-utilized

The “Overlay” Solution
Physical Logical Routing at layer 2 (ATM or FR) is used for traffic engineering Analogy to direct highways between SFO-LAX & SAN-SMF. Nobody enters the highway in between.

Traffic engineering with overlay
PVC for R2 to R3 traffic PVC for R1 to R3 traffic

“Overlay” solution: drawbacks
Extra network devices (cost) More complex network management (cost) two-level network without integrated network management additional training, technical support, field engineering IGP routing scalability issue for meshes Additional bandwidth overhead (“cell tax”)

Traffic engineering with Layer 3
IP routing: destination-based least-cost routing under-utilized alternate path Path for R2 to R3 traffic Path for R1 to R3 traffic

Traffic engineering with Layer 3
IP routing: destination-based least-cost routing Path for R2 to R3 traffic Path for R1 to R3 traffic under-utilized alternate path

Traffic engineering with Layer 3 what is missing ?
Path computation based just on IGP metric is not enough Support for “explicit” routing (aka “source routing”) is not available Analogy: San Jose San Jose What makes the current Layer 3 routing capabilities so inadequate for traffic engineering is the lack of support for explicit routing. The current forwarding paradigm, centered around “destination-based” is clearly inadequate. And likewise, relying just on IGP metric as the only traffic engineering tool is not good enough.

MPLS Traffic Engineering
© 1999, Cisco Systems, Inc. 14

TE - key mechanisms “Explicit” routing (aka “source routing”)
Constrained-based Path Selection Algorithm (Example: Choose path with no congestion, avoid highways, select scenic roads etc…) Extensions to OSPF/ISIS for flooding of resources / policy information (Live collection of traffic statistics - pilot tests in Europe) MPLS as the forwarding mechanism (Auto Pilot programmed in each car when entering city)

TE - key mechanisms “Explicit” routing (aka “source routing”)
RSVP as the mechanism for establishing Label Switched Paths (LSPs) use of the explicitly routed LSP’s in the forwarding table

What is a “traffic trunk” ?
B D C Aggregation of (micro) flows that are: forwarded along a common path (within a service provider) often from a POP to another POP share a common QoS requirement (if L-LSPs are used) Essential for scalability

TE basics Traffic within a Service Provider as a collection of “POP to POP traffic trunks” with known bandwidth and policy requirements TE provides traffic trunk routing that meets the goal of Traffic Engineering via a combination of on-line and off-line procedures

Requirements: Differentiating traffic trunks: Handling failures:
large, ‘critical’ traffic trunks must be well routed in preference to other trunks Handling failures: automated re-routing in the presence of failures Pre-configured paths: for use in conjunction with the off-line route computation procedures Support of multiple Classes of Service

Requirements (cont.) Constraining sub-optimality:
should re-optimize on new/restored bandwidth in a non-disruptive fashion - maintain the existing route until the new route is established, without any double counting Ability to “spread” traffic trunk across multiple Label Switched Paths (LSPs) could provide more efficient use of networking resources Ability to include / exclude certain links for certain traffic trunks

Design Constraints Constrained to a single routing domain
initially constrained to a single area Requires OSPF or IS-IS Unicast traffic Focus on supporting routing based on a combination of administrative + bandwidth constraints

Trunk Attributes Configured at the head-end of the trunk Bandwidth
Priorities setup priority: priority for taking a resource holding priority: priority for holding a resource

Trunk attributes Ordered list of Path Options Re-optimization
possible administratively specified paths (via an off-line central server) - {explicit list} Constrained-based Dynamically computed paths based on combo of Bw and policies Re-optimization each path option is enabled or not for re-optimization, interval given in seconds. Max 1 week (7*24*3600), Disable 0, Def 1h.

Trunk Attributes Resource class affinity (Policy)
supports the ability to include/exclude certain links for certain traffic trunks based on a user-defined Policy Tunnel is characterized by a 32-bit resource-class affinity bit string 32-bit resource-class mask (0= don’t care, I care) Link is characterized by a 32-bit resource-class attribute string Default-value of tunnel/link bits is 0 Default value of the tunnel mask = 0x0000FFFF

Example0: 4-bit string, default
C A 0000 B 0000 0000 0000 0000 D E Trunk A to B: tunnel = 0000, t-mask = 0011 ADEB and ADCEB are possible

Example1a: 4-bit string C A 0000 B 0000 0000 0000 0010 D E Setting a link bit in the lower half drives all tunnels off the link, except those specially configured Trunk A to B: tunnel = 0000, t-mask = 0011 Only ADCEB is possible

Example1b: 4-bit string C A 0000 B 0000 0000 0000 0010 D E A specific tunnel can then be configured to allow such links by clearing the bit in its affinity attribute mask Trunk A to B: tunnel = 0000, t-mask = 0001 Again, ADEB and ADCEB are possible

Example1c: 4-bit string C A 0000 B 0000 0000 0000 0010 D E A specific tunnel can be restricted to only such links by instead turning on the bit in its affinity attribute bits Trunk A to B: tunnel = 0010, t-mask = 0011 No path is possible

Example2a: 4-bit string C A 0000 B 0000 0000 0000 0100 D E Setting a link bit in the upper half drives has no immediate effect Trunk A to B: tunnel = 0000, t-mask = 0011 ADEB and ADCEB are both possible

Example2b: 4-bit string C A 0000 B 0000 0000 0000 0100 D E A specific tunnel can be driven off the link by setting the bit in its mask Trunk A to B: tunnel = 0000, t-mask = 0111 Only ADCEB is possible

Example2c: 4-bit string C A 0000 B 0000 0000 0000 0100 D E A specific tunnel can be restricted to only such links Trunk A to B: tunnel = 0100, t-mask = 0111 No path is possible

Trunk Attribute Resource Class Affinity (Policy)
The user defines the semantics: this bit/mask says “low-delay path excluded” Flexible (maybe too flexible :) 1c vs 2c ?… in 1c, the default tunnels will not be willing to flow via the special links

Link Attributes and their flooding

Link Resource Attributes
Resource attributes are configured on every link in a network bandwidth Link Attributes TE-specific link metric

Link Resource Attributes
Resource attributes are flooded throughout the network bandwidth per priority (0-7) Link Attributes (Policy) TE-specific link metric draft-li-mpls-igp-te-00.txt

Per-Priority Available BW
D T=0 Link L, BW=100 D advertises: AB(0)=100=…= AB(7)=100 AB(i) = ‘Available Bandwidth at priority I” T=1 Setup of a tunnel over L at priority=3 for 30 units D T=2 Link L, BW=100 D advertises: AB(0)=AB(1)=AB(2)= AB(3)=AB(4)=…=AB(7)=70 T=3 Setup of an additional tunnel over L at priority=5 for 30 units D T=4 Link L, BW=100 D advertises: AB(0)=AB(1)=AB(2)= AB(3)=AB(4)= AB(5)=AB(6)=AB(7)=40

Information Distribution
Re-use the flooding service from the Link-State IGP opaque LSA for OSPF draft-katz-yeung-ospf-traffic-00.txt new wide TLV for IS-IS draft-ietf-isis-traffic-00.txt

Information Distribution
Periodic (timer-based) On significant changes of available bandwidth (threshold scheme) On link configuration changes On LSP Setup failure

Periodic Timer Periodically, a node checks if the current TE status is the same as the one lastly broadcasted. If different, it floods its updated TE Links status

Significant Change Each time a threshold is crossed, an update is sent
Denser population as utilization increases Different thresholds for UP and Down (stabler) 100% 92% Update 85% 70% 50% Update

LSP Setup Failure Due to the threshold scheme, it is possible that one node thinks he can signal an LSP tunnel via node Z while in fact, Z does not have the required resources When Z receives the Resv message and refuses the LSP tunnel, it broadcasts an update of its status

Constrained-based Computation

Constrained-Based Routing
“In general, path computation for an LSP may seek to satisfy a set of requirements associated with the LSP, taking into account a set of constraints imposed by administrative policies and the prevailing state of the network -- which usually relates to topology data and resource availability. Computation of an engineered path that satisfies an arbitrary set of constraints is referred to as "constraint based routing” Draft-li-mpls-igp-te-00.txt

Path Computation “On demand” by the trunk’s head-end: for a new trunk
for an existing trunk whose (current) LSP failed for an existing trunk when doing re-optimization

Path Computation Input:
configured attributes of traffic trunks originated at this router attributes associated with resources available from IS-IS or OSPF topology state information

Path Computation Prune links if: Compute shortest distance path
insufficient resources (e.g., bandwidth) violates policy constraints Compute shortest distance path TE uses its own metric Tie-break: selects the path with the highest minimum bandwdith so far, then with the smallest hop-count

Path Computation Output:
explicit route - expressed as a sequence of router IP addresses interface addresses for numbered links loopback address for unnumbered links used as an input to the path setup component

Example Tunnel’s request: Priority 3, BW = 30 units,
C BW(3)=80 1000 A 0100 B BW(3)=60 0000 0000 0000 BW(3)=80 D BW(3)=20 BW(3)=50 E 0010 1000 BW(3)=70 BW(3)=50 G Tunnel’s request: Priority 3, BW = 30 units, Policy string: 0000, mask: 0011

MPLS as the forwarding mechanism

MPLS Labels Two types of MPLS Labels: Prefix Labels & Tunnel Labels
LDP RSVP MP-BGP CR-LDP PIM Distributed by:

MPLS as forwarding engine
Traffic engineering requires explicit routing capability IP supports only the destination-based routing not adequate for traffic engineering MPLS provides simple and efficient support for explicit routing label swapping separation of routing and forwarding

RSVP Extensions to RFC2205 for LSP Tunnels
downstream-on-demand label distribution instantiation of explicit label switched paths allocation of network resources (e.g., bandwidth) to explicit LSPs rerouting of established LSP-tunnels in a smooth fashion using the concept of make-before-break tracking of the actual route traversed by an LSP-tunnel diagnostics on LSP-tunnels the concept of nodal abstraction preemption options that are administratively controllable draft-ietf-mpls-rsvp-lsp-tunnel-0X.txt

RSVP Extensions: new objects
LABEL_REQUEST found in Path LABEL found in Resv EXPLICIT_ROUTE found in Path RECORD_ROUTE found in Path, Resv SESSION_ATTRIBUTE found in Path 0x01 Fast Reroute Capable, 0x02 Permit Merging, 0x04 May Reoptimize => SE New C-Types are also assigned for the SESSION, SENDER_TEMPLATE, FILTER_SPEC, FLOWSPEC objects. All new objects are optional with respect to RSVP (RFC2205). The LABEL_REQUEST and LABEL objects are mandatory with respect to MPLS LSP signalisation specification.

LSP Setup Initiated at the head-end of a trunk
Uses RSVP (with extensions) to establish Label Switched Paths (LSPs) for traffic trunks

Path Setup - Example R8 R9 R3 R4 R2 Pop R5 R1 Label 32 Label 49 R6 R7 Label 17 Label 22 Setup: Path (ERO = R1->R2->R6->R7->R4->R9) Reply: Resv communicates labels and reserves bandwidth on each link

Path Setup - more details
2 1 2 1 Path: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R1-2) Label_Request(IP) ERO (R2-1, R3-1) Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 00) Sender_Tspec(2Mbps) Record_Route(R1-2)

2 1 2 1 Path State: Session(R3-lo0, 0, R1-lo0) PHOP(R1-2) Label_Request(IP) ERO (R2-1, R3-1) Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 00) Sender_Tspec(2Mbps) Record_Route (R1-2)

2 1 2 1 Path: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R2-2) Label_Request(IP) ERO (R3-1) Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 00) Sender_Tspec(2Mbps) Record_Route (R1-2, R2-2)

2 1 2 1 Path State: Session(R3-lo0, 0, R1-lo0) PHOP(R2-2) Label_Request(IP) ERO () Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 00) Sender_Tspec(2Mbps) Record_Route (R1-2, R2-2, R3-1)

2 1 2 1 Resv: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R3-1) Style=SE FlowSpec(2Mbps) Sender_Template(R1-lo0, 00) Label=POP Record_Route(R3-1)

2 1 2 1 Resv State Session(R3-lo0, 0, R1-lo0) PHOP(R3-1) Style=SE FlowSpec (2Mbps) Sender_Template(R1-lo0, 00) OutLabel=POP IntLabel=5 Record_Route(R3-1)

2 1 2 1 Resv: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R2-1) Style=SE FlowSpec (2Mbps) Sender_Template(R1-lo0, 00) Label=5 Record_Route(R2-1, R3-1)

2 1 2 1 Resv state: Session(R3-lo0, 0, R1-lo0) PHOP(R2-1) Style=SE FlowSpec (2Mbps) Sender_Template(R1-lo0, 00) Label=5 Record_Route(R1-2, R2-1, R3-1)

Trunk Admission Control
Performed by routers along a Label Switched Path (LSP) Determines if resources are available May tear down (existing) LSPs with a lower priority Does the local accounting Triggers IGP information distribution when resource thresholds are crossed

Link Admission Control
Already invoked by Path message if BW is available, this BW is put aside in a waiting pool (waiting for the RESV msg) if this process required the pre-emption of resources, LCAC notified RSVP of the pre-emption which then sent PathErr and/or ResvErr for the preempted tunnel if BW is not available, LCAC says “No” to RSVP and a Path error is sent. A flooding of the node’s resource info is triggered, if needed ”draft-ietf-mpls-rsvp-lsp-tunnel-02.txt”

Path Monitoring Use of new Record Route Object
keep track of the exact tunnel path detects loops copy of RRO to ERO allows for route pinning

Path Re-Optimization Looks for opportunities to re-optimize
make before break no double counting of reservations via RSVP “shared explicit” style!

Non-disruptive rerouting - new path setup
Pop R5 R1 32 49 R6 R7 17 22 Current Path (ERO = R1->R2->R6->R7->R4->R9) New Path (ERO = R1->R2->R3->R4->R9) - shared with Current Path Until R9 gets new Path Message, current Resv is refreshed

Non-disruptive rerouting - switching paths
Pop 26 89 R5 R1 32 38 49 R6 R7 17 22 Resv: allocates labels for both paths Reserves bandwidth once per link PathTear can then be sent to remove old path (and release resources)

Reroute - More Details ERO (R2-1, R3-1) Sender_Template(R1-lo0, 00)
Session(R3-lo0, 0, R1-lo0) 00 R1 R3 2 R2 1 2 1 3 01 3 01 01 This section describes how to setup a tunnel that is capable of maintaining resource reservations (without double counting) while it is being rerouted or while it is attempting to increase its bandwidth. In the initial Path message, the ingress node forms a SESSION object, assigns a Tunnel_ID, and places its IPv4 address in the Extended_Tunnel_ID It also forms a SENDER_TEMPLATE and assigns a LSP_ID. Tunnel setup then proceeds according to the normal procedure. On receipt of the Path message, the egress node sends a Resv message with the STYLE Shared Explicit toward the ingress node. When an ingress node with an established path wants to change that path, it forms a new Path message as follows. The existing SESSION object is used. In particular the Tunnel_ID and Extended_Tunnel_ID are unchanged. The ingress node picks a new LSP_ID to form a new SENDER_TEMPLATE. It creates an EXPLICIT_ROUTE object for the new route. The new Path message is sent. The ingress node refreshes both the old and new path messages The egress node responds with a Resv message with an SE flow descriptor formatted as: <FLOWSPEC><old_FILTER_SPEC><old_LABEL_OBJECT><new_FILTER_SPEC> <new_LABEL_OBJECT> (Note that if the PHOPs are different, then two messages are sent each with the appropriate FILTER_SPEC and LABEL_OBJECT.) When the ingress node receives the Resv Message(s), it may begin using the new route. It should send a PathTear message for the old route. ERO (R2-1, …, R3-3) Sender_Template(R1-lo0, 01) Resource Sharing

Reroute - More Details R3 R1 R2 2 1 2 1 3 3 Path: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R1-2) Label_Request(IP) ERO (R2-1, …,R3-3) Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 01) Sender_Tspec(3Mbps) Record_Route(R1-2)

Reroute - More Details R3 R1 R2 2 1 3 3 Path State: Session(R3-lo0, 0, R1-lo0) PHOP(R1-2) Label_Request(IP) ERO (R2-1, …,R3-3) Session_Attribute (S(3), H(3), 0x04) Sender_Template(R1-lo0, 01) Sender_Tspec(3Mbps) Record_Route (R1-2)

Reroute - More Details R3 R1 R2 2 1 3 3

Reroute - More Details R3 R1 R2 2 1 3 3 RSVP: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R3-3) Style=SE FlowSpec(3Mbps) Sender_Template(R1-lo0, 01) Label=POP Record_Route(R3-3)

Reroute - More Details R3 R1 R2 2 1 3 3

Reroute - More Details R3 R1 R2 2 1 3 3 RSVP: Common_Header Session(R3-lo0, 0, R1-lo0) PHOP(R2-1) Style=SE FlowSpec (3Mbps) Sender_Template(R1-lo0, 01) Label=6 Record_Route(R2-1, …, R3-3) Sender_Template(R1-lo0, 00) Label=5 Record_Route(R2-1, R3-1)

Reroute - More Details R3 R1 R2 2 1 3 3 RSVP state: Session(R3-lo0, 0, R1-lo0) PHOP(R2-1) Style=SE FlowSpec Sender_Template(R1-lo0, 01) Label=6 Record_Route(R2-1, …, R3-3) Sender_Template(R1-lo0, 00) Label=5 Record_Route(R2-1, R3-1)

Fast Restoration Handling link failures - two complementary mechanisms: Path protection Link/Node protection

Path Protection Step1: link failure detection
O(depends on L2/L1) Step2a: IGP reaction (ISIS case) Either via Step1 or via IGP hello expiration (30s by default for ISIS) 5s (default) must occur by default before the generation of a new LSP 5.5s (default) must occur before a change of the LSPDB and the consecutive SPF run. The next SPF run can only occur 10s after (default) Flooding time (LSP are paced (16ms for first LSP, 33ms between LSP’s, depend also on link speed) Once the RIB is updated, this change must be incorporated into CEF. The Head-end finally computes the new topology and finds out that some established LSP’s are affected. It schedules a reoptimization for them

Path Protection Step2b: RSVP signalisation
rsvp path states with the failed intf as oif is detected check if another oif available (if loose ero) if not, clear path state and send tear to head-end Step2: Either stepA or stepB alarms the head-end Step3: Re-optimization dijkstra computation: O(0.5)ms per node (rule of thumb) RSVP signalisation time to instal rerouted tunnel convergence in the order of several seconds (at least).

Path Protection Speed it Up
Fine Tune the IGP convergence Through adequate tuning, ISIS could be tuned to converge in 2-3s, this ensuring that the convergence time bottleneck is the signalisation time for the new tunnel. Several tunnels in parallel with load-babalancing if combined with the IGP convergence, the path resilience could be brought to around 2-3s One end-2-end tunnel in parallel but in backup mode feature under development (Fast Path Protection)

Fast ReRoute (aka Link Protection) An Overview

Objective FRR allows for temporarily routing around a failed link or node while the head-end may reoptimize the entire LSP rerouting under 50ms scalable (must support lots of LSP’s)

Fast reroute Overview Controlled by the routers at ends of a failed link link protection is configured on a per link basis Session_Attribute’s Flag 0x01 allows the use of Link Protection for the signalled LSP Uses nested LSPs (stack of labels) original LSP nested within link protection LSP

Static backup Tunnel Setup: Path (R2->R6->R7->R4)
Pop R6 R7 17 22 Setup: Path (R2->R6->R7->R4) Labels Established on Resv message

Routing prior R2-R4 link failure
Pop R5 R1 14 37 R7 R6 Setup: Path (R1->R2->R4->R9) Labels Established on Resv message

Link Protection Active
On failure of link from R2 -> R4, R2 simply changes outgoing Label Stack from 14 to <17, 14>

Link Protection Active
Pop 14 Swap 37->14 Push 17 R4 R2 Push 37 R5 R1 R7 R6 Swap 17->22 Pop 22 Label Stack: R1 R2 R6 R7 R4 R9 None 14 14

Fast ReRoute More details on Link Protection (FRR v1)

V1 Constrain We protect the facility (link), not individual LSP’s
scalability vs granularity No node resilience Static backup tunnel The protected link must use the Global Label space A backup tunnel can backup at most one link, but n LSPs travelling via this link

Terminology R8 R9 R4 R2 R1 R5 R7 R6 LSP: end-to-end tunnel onto which data normally flows (eg R1 to R9) BackUp tunnel: temporary route to take in the event of a failure

Terminology Link Protection
In the event of a link failure, an LSP is rerouted to the next-hop using a preconfigured backup tunnel

How to indicate a link is protected and which tunnel is the backup?
On R2 (For LSP’s flowing from R2 to R4): interface pos <r2tor4> mpls traffic-eng backup tunnel 1000 link LSP’s are unidirectional, so the same protection should be enable for the opposite direction if reverse LSP is conf.

How to setup the backup tunnel?
Just as a normal tunnel whose head-end is R2 and tail-end is R4 v1 requires a manually configured ERO interface Tunnel1000 ip unnumbered Loopback0 tunnel destination R4 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 7 7 tunnel mpls traffic-eng bandwidth 800 tunnel mpls traffic-eng path-option 1 explicit name backuppath1 ip explicit-path name backuppath1 enable next-address R6 next-address R7 next-address R4

Which LSP’s can be rerouted on R2 in the event of R2-R4 failure?
The LSP’s flowing through R2 that have R2-R4 as Outgoing Interface have been signalled by their respective head-ends with a session attribute flag 0x01=ON (may use fast-reroute tunnels) int tunnel 1 ## config on the head-end tunnel mpls traffic-eng fast-reroute

Global Label Allocation
R8 POP R9 14 R4 R2 R1 R5 R7 R6 For the blue LSP, R4 bound a global label of 14 Any MPLS frame received by R4, with label 14, will be switched onto the link to R9 with a POP, whatever the incoming interface

How fast is fast? Link Failure Notification
Usual PoS alarm detection PoS driver optimisation to interrupt RP in < 1ms Expected call to net_cstate(idb, UP/DOWN) identifying the DOWN state of the protected int to start our protection action. RP updates the master TFIB (replace a swap by a swap-push) < 1ms Master TFIB change notified to the linecards

Path state while Rerouting
Path (…, PHOP=R2, …) R8 R9 Path state Path state BackUP tunnel R4 R2 R1 R5 R7 R6 PathError (Reservation in Place)

Path & Resv Msgs [Error & Tear]
When no link protection: Conf. Resv Tear Conf. Path Tear Resv Tear When link protection: Path Error R4 waits for refresh Resv in place

LSP reoptimization Head-end notified by PathError
special flag (reservation in place) indicates that the path states must not be destroyed. It is just a hint to the head-end that the path should be reoptimized Head-end notified by IGP

Why the Patherror? Reliable PathErr optimization
The Patherror might be faster In case of multi-area IGP, the IGP will not provide the information In case of very fast up-down-up, the LSP will be put on the backup tunnel and will stay there as the IGP will not have originated a new LSP/LSA a router waits a certain time before originating a new LSP/LSA after a topological change Reliable PathErr optimization

Resv state while Rerouting
The loss of the interface does not affect the Path and Resv states for the LSP’s received on that interface that are marked fast reroutable! R8 R9 BackUP tunnel Resv state Resv state R4 R2 R1 R5 Resv R7 R6 Resv Message is unicast to the Phop (R2) R2’s Path State has been informed that the Resv might arrive over a different intf as the one used by the Path message

DiffServ and LSP Reoptimization
In order to optimize the bandwdith usage, backup tunnels might be configured with 0kbps no ‘non-working’ bandwdith as in SDH! Although usually the backbone is though as being congestion-free, during rerouting some local congestion might occur Use diffserv to handle this short-term congestion Use LSP reoptimization to handle the long-term congestion

Layer1/2 and Layer3 Backup Tunnel should not use
the protected L3 link the protected L1/L2 links!!! Use WANDL (loaded with both L3 and L1/2 topologies) to compute the best paths for backup tunnels Download this as static backup tunnels to the routers

Fast ReRoute Node Protection

Backup Tunnel to the next-hop of the LSP’s next-hop
Overview R8 R9 R4 R3 R2 R5 R1 R7 R6 Backup Tunnel to the next-hop of the LSP’s next-hop

A few More details Assume R2 is configured with resilience for R3
R2 receives a path message for a new LSP whose ERO is {R3, R4, …}, whose Session is (R9, 1, R1), whose sender is (R1, 1) and whose session attribute is (0x01 ON, 0x02 OFF) 0x01: may use local fast-reroute if available 0x02: merge capable

A few More details Then R2 checks if it already has a tunnel to R4
If not, R2 builds a backup tunnel to R4 (currently just like in link protection - manual explicit setup). R2 sends a Path onto the tunnel with Session (R9, 1, R1), Sender (R2, 1), Session Attribute (0x01 OFF, 0x02 ON) and PHOP R2

A few More details When R4 receives this Path message,
it matches the session with the LSP’s one merge (and thus stop) this path message sends a RESV back to R2 (unicast) and allocate the appropriate label L

A few More details When R2 detects R3’s failure,
For the TFIB entry for the LSP, R2 changes the existing ‘swap’ by a ‘swap to L’ and a ‘push of the backup tunnel label’ R4’s states are refreshed by the secondary path messages (over the backup tunnels) ERO of the original path is adjusted at R2 NHOP is modified in R2 (from R3 to R4) PHOP is modified in R4 (from R3 to R2)

A few More Details RESV is being sent back from R4 to R2 directly
If R3 is still active and just the R2-R3 link failed R4 needs to ignore & drop any Tear-Down msg R3 would be sending after the termination of reception of path refreshes from R2.

How to detect R3’s failure?
A node may fail while the link is still up A node’s linecard processes might survive, a main process failure (freeze of the RP process)

A possible solution Keepalives between LC’s
RP RP LC LC ... LC Keepalives between LC’s Keepalives between a LC and its master RP

Assigning traffic to Paths (aka autoroute)

Enhancement to SPF During SPF each new node found is moved from a TENTative list to PATHS list. Now the first-hop is being determined via: A. Check if there is any TE tunnel terminating at this node from the current router and if so do the metric check B. If there is no TE tunnel and the node is directly connected use the first-hop from adj database C. In non of the above applies the first-hop is copied from the parent of this new node.

Enhancement to SPF - metric check
Tunnel metric: A. Relative +/- X B. Absolute Y The default is relative metric of 0. Example: Metric of native IP path to the found node = 50 1. Tunnel with relative metric of -10 => 40 2. Tunnel with relative metric of +10 => 60 3. Tunnel with absolute metric of 10 => 10

Enhancement to SPF - metric check
If the metric of the found TE tunnel at this node is higher then the metric for other tunnels or native IGP path this tunnel is not installed as next hop If the metric of the found TE tunnel is equal to other TE tunnels the tunnel is added to the existing next-hops If the metric of the found TE tunnel is lower then the metric of other TE tunnels or native IGP the tunnel replaces them as the only next-hop.

Auto-Bandwidth Global command: Monitor marked tunnels’ 5-min average counters every X minutes default: X = 300 (seconds) (config)# mpls traffic-eng auto-bw timers frequency <seconds>

Auto-Bandwidth Per tunnel command:
Every Y minutes, update the BW constraint of the tunnel with the maximum of: the largest 5-min values sampled during the last Y minutes (Def Y = 24 * 3600sec) - 24h a configured maximum value (config-if)# tunnel mpls traffic-eng auto-bw {frequency <seconds>} {max-bw <kbs>} if the new Bw is not available, the old one is maintained (the new BW is signalled via a 2nd tunnel to follow make before break model)

Example

Verbatim Applies to explicitly routed LSP’s
Disable any check against TE/IGP database of the head end RSVP still check BW (and policy when this will be in Path) hop by hop Application: manual TE through multi-area IGP CLI: tunnel mpls traffic-eng path-option verbatim

In-Progress Allows an end-head to account for bw consumed by tunnels that it has just signalled and for whom the IGP LSA/LSP update has not reflected the available bandwdith

Example In-Prog Bw: 10 In-Prog Bw: 55 Avail Bw: 100
All tunnels require 45 units of BW In-progress counters reset upon new LSA/LSP reception In-progress counter decremented upon receipt of path-error

Benefits Speed-up the installation of tunnels as it avoids spending time trying not working solutions Allows for better load-balancing igp metric then max(min(path-bw)!

Under/Overbook ML: Maximum link bandwidth:
This sub-TLV contains the maximum bandwidth that can be used on this link in this direction (from the system originating the LSP to its neighbors). This is useful for traffic engineering. MR: Maximum reservable link bandwidth: This sub-TLV contains the maximum amount of bandwidth that can be reserved in this direction on this link. Note that for oversubscription purposes, this can be greater than the bandwidth of the link. UR(I): Unreserved bandwidth at Priority i: This sub-TLV contains the amount of bandwidth reservable on this direction on this link, at a certain priority. Note that for oversubscription purposes, this can be greater than the bandwidth of the link.

Under/Overbook Physical T1 ... A B ... s0 ML is set to B1 (eg 1500)
A’s config: int s0 bandwidth <B1> (eg 1500 kbps) ip rsvp bandwdith <B2> (eg 4000 kbps) Physical T1 ... A B ... s0 ML is set to B1 (eg 1500) MR is set to B2 (eg 4000) At t=0, for all i 0 to 7, UB(i) = M = (eg 4000) routerA's LCAC will not accept an LSP tunnel asking more than ML even if there is available bandwdith at the requested priority. However, LCAC would allow for example 5 trunks each asking 700 kbps (thus each asking less than ML) while the aggregate is smaller than MR: because { 700 < ML=1500 } and { 3500 < MR=4000 }

Standby Current solution
Tu1: bw1 A B Tu2: bw2 Tu3: bw3 Tu4: bw4 Solution: 4 tunnels from A to B: Tu1’s relative metric: -3 Tu2 and tu3’s relative metric: -2 Tu4’s relative metric: -1

Last hop label IETF draft-ietf-mpls-label-encaps-07.txt
A value of 0 represents the "IPv4 Explicit NULL Label” A value of 1 represents the "Router Alert Label” A value of 2 represents the "IPv6 Explicit NULL Label" A value of 3 represents the "Implicit NULL Label” New cli forces tailend to send implicit-null (3) instead of explicit null (0) - default. # [no] mpls traffic-eng signalling advertise implicit-null [<acl>] On receipt (n-1) node we must map 0, 1 or 3 to internal Implicit Null [1 only for historical reasons]

QoS and RRR MPLS TE can operate simultaneously (and orthogonally) with MPLS Diff-Serv All Precedence/DSCP packets follow the same TE tunnels Diff-Serv provides selective discard (via WRED), and selective scheduling (via WFQ)

QoS and RRR Future: Scalable per-tunnel scheduling and policing
Guaranteed PIPE in MPLS-VPN CoS per-DSCP/per-FEC traffic engineering diffserv backbone capacity management

DiffServ and fast-reroute/TE
In order to optimize the bandwdith usage, backup tunnels might be configured with 0kbps no ‘non-working’ bandwdith as in SDH! Although usually the backbone is though as being congestion-free, during rerouting some local congestion might occur Use diffserv to handle this short-term congestion Use LSP reoptimization to handle the long-term congestion

RSVP LSP Signalling Protocol for Traffic Engineering

MPLS-TE Signalling Protocol
Two proposed signaling mechanisms for MPLS traffic engineering are being considered by the IETF’s MPLS work group RSVP (Cisco and a number of Gigabit router startups (Avici, Argon, Ironbridge, Juniper, and Torrent)) CR-LDP (Ericsson, Ennovate, GDC, Nortel)

An IP signalling Protocol!
Why RSVP ? What is needed: ability to establish and maintain Label Switched Path along an explicit route ability to reserve resources when establishing a path Interdependent, not independent tasks benefit from consolidation An IP signalling Protocol!

Do I need RSVP only for TE ?
Other uses of RSVP in today’s networks: Voice over IP call setup, Video (IPTV) Hybrid deployments (only where needed) QoS DiffServ Engineering (Cops) Qualitative Service for DiffServ with RSVP (as opposed to Quantitative RSVP IntServ model) NO !

RSVP is a natural choice
RFC2205: “provides a general facility for creating and maintaining distributed reservation state across a mesh of multicast and unicast delivery paths” TE: use as a general facility for creating and maintaining distributed forwarding & reservation state across a mesh of delivery paths

RFC2205: “transfers and manipulates QoS control parameters as opaque data, passing them to the appropriate traffic control module for interpretation” TE: transfer and manipulate explicit route and label control parameters as opaque data pass explicit route parameter to the appropriate routing module, and label parameter to the MPLS module

Leverage Standardized Protocols PIM for Multicast MPLS BGP for MPLS VPN’s RSVP for MPLS Traffic Engineering LDP (TDP) has been designed because it was easier than fixing all IGP’s (RIP, EIGRP, OSPF, ISIS) fast deployments and engineering consistency Leverage Deployed Experience RSVP deployed since 1996 (IOS 11.2) ww.isi.edu/rsvp/DOCUMENTS/ietf_rsvp_qos_survey for a list of RSVP implementations

RSVP easily supports Dynamic resizing of tunnels or paths through refresh messages Supports strict as well as loose source routes No double counting of bandwidth when re-routing sub-optimal routes Extensible via definition of new objects

RSVP/TE and Scalability
Very Different than IntServ context State applies to a collection of flows (i.e. a traffic trunk), rather than to a single (micro) flow RSVP sessions are used between routers, not hosts Sessions are long-lived (up to a few weeks) Paths are not bound by destination-based routing Reference: ‘Applicability Statement for Extensions to RSVP for LSP-Tunnels’ (draft-awduche-mpls-rsvp-tunnel-applicability-01.txt)

RSVP/TE and Scalability Very Different than IntServ context
RFC2208: “the resource requirements for running RSVP on a router increases proportionally with the number of separate sessions” TE: that is why using traffic trunks to aggregate flows is essential RFC2208: “supporting numerous small reservations on a high-bandwidth link may easily overtax the routers and is inadvisable” TE : n/a in the context of TE - traffic trunks aggregate multiple flows

TE/RSVP Scalability With basic RSVP (RFC2205), RRR LSP tunnels flowing through a 75x0 or is not a problem Already Deployed on a number of Tier-1 ISP backbones Ship with 12.0(5)S Refresh Aggregation work will again enhance this scalability

Conclusion Using RSVP as MPLS/TE signalling protocol is the natural and consistent choice It is however only one part of a whole solution: MPLS as forwarding engine IGP (OSPF/ISIS) extensions Constrained Base Routing (RRR) RSVP as MPLS/TE Signalling Protocol Installation of Tunnels in the FIB

Traffic Eng Provides traffic engineering capabilities at Layer 3
above and beyond of what is provided with ATM Could be used for other applications as well Shipping and deployed in production

MPLS Traffic Engineering NANOG18 Robert Raszuk - IOS Engineering

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MPLS Traffic Engineering NANOG18 Robert Raszuk - IOS Engineering

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