MPLS Traffic
Engineering
NANOG18
Robert Raszuk - IOS Engineering
raszuk@cisco.com
© 1999, Cisco Systems, Inc.
1
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
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
2
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
The ultimate goal is cost saving !
NANOG18 - Robert Raszuk
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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)
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© 2000, Cisco Systems, Inc.
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Without Traffic Engineering
Cars:
SFO-LAX
SAN-SMF
LAX-SFO
SMF-SAN
No Traffic
Engineering
analogy
to Human
Drivers
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With Traffic Engineering
Cars:
SFO-LAX
SAN-SMF
LAX-SFO
SMF-SAN
Traffic
Engineering
analogy
to Auto Pilot
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Routing solution to Traffic
Engineering
R2
R3
R1
• 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 underutilized
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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The “Overlay” Solution
L3
L3
L2
L3
L2
L2
L2
L3
L2
L2
L3
L3
L3
L3
L3
L3
L3
L3
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.
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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Traffic engineering with overlay
R2
R3
R1
PVC for R2 to R3 traffic
PVC for R1 to R3 traffic
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“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”)
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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Traffic engineering with Layer 3
R2
R3
R1
IP routing: destination-based least-cost routing
Path for R2 to R3 traffic
Path for R1 to R3 traffic
under-utilized alternate path
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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Traffic engineering with Layer 3
R2
R3
R1
IP routing: destination-based least-cost routing
Path for R2 to R3 traffic
Path for R1 to R3 traffic
under-utilized alternate path
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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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:
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
San
San
Jose
Jose
13
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)
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© 2000, Cisco Systems, Inc.
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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
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What is a “traffic trunk” ?
A
D
B
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
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© 2000, Cisco Systems, Inc.
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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 offline procedures
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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Requirements:
• Differentiating traffic trunks:
– 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
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© 2000, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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Trunks Attributes
© 1999, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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Trunk attributes
• Ordered list of Path Options
– 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 reoptimization, interval given in seconds.
– Max 1 week (7*24*3600), Disable 0, Def 1h.
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© 2000, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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Example0: 4-bit string, default
C
A
0000
0000
B
0000
0000
0000
D
E
• Trunk A to B:
– tunnel = 0000, t-mask = 0011
• ADEB and ADCEB are possible
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Example1a: 4-bit string
C
A
0000
0000
B
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
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© 2000, Cisco Systems, Inc.
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Example1b: 4-bit string
C
A
0000
0000
B
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
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© 2000, Cisco Systems, Inc.
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Example1c: 4-bit string
C
A
0000
0000
B
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
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© 2000, Cisco Systems, Inc.
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Example2a: 4-bit string
C
A
0000
0000
B
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
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© 2000, Cisco Systems, Inc.
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Example2b: 4-bit string
C
A
0000
0000
B
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
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© 2000, Cisco Systems, Inc.
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Example2c: 4-bit string
C
A
0000
0000
B
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
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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
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Link Attributes and
their flooding
© 1999, Cisco Systems, Inc.
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Link Resource Attributes
• Resource attributes are configured on
every link in a network
– bandwidth
– Link Attributes
– TE-specific link metric
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© 2000, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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Per-Priority Available BW
D
T=0
T=1
D advertises: AB(0)=100=…= AB(7)=100
AB(i) = ‘Available Bandwidth at priority I”
Setup of a tunnel over L at priority=3 for 30 units
D
T=2
T=3
Link L, BW=100
Link L, BW=100
D advertises: AB(0)=AB(1)=AB(2)=100
AB(3)=AB(4)=…=AB(7)=70
Setup of an additional tunnel over L at priority=5 for 30 units
D
T=4
NANOG18 - Robert Raszuk
Link L, BW=100
© 2000, Cisco Systems, Inc.
D advertises: AB(0)=AB(1)=AB(2)=100
AB(3)=AB(4)=70
AB(5)=AB(6)=AB(7)=40
37
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
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© 2000, Cisco Systems, Inc.
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Information Distribution
• Periodic (timer-based)
• On significant changes of available
bandwidth (threshold scheme)
• On link configuration changes
• On LSP Setup failure
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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
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Significant Change
100%
92%
85%
70%
Update
50%
Update
• Each time a threshold is
crossed, an update is
sent
• Denser population as
utilization increases
• Different thresholds for
UP and Down (stabler)
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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
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© 2000, Cisco Systems, Inc.
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Constrained-based
Computation
© 1999, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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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 reoptimization
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© 2000, Cisco Systems, Inc.
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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
• available from IS-IS or OSPF
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© 2000, Cisco Systems, Inc.
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Path Computation
• Prune links if:
– 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
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© 2000, Cisco Systems, Inc.
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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
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© 2000, Cisco Systems, Inc.
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Example
C
BW(3)=80
0100
1000
BW(3)=60
A
0000
BW(3)=50
D
0000
BW(3)=20
E
B
0000
BW(3)=80
0010
BW(3)=70
1000
BW(3)=50
G
• Tunnel’s request:
– Priority 3, BW = 30 units,
– Policy string: 0000, mask: 0011
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MPLS as the forwarding
mechanism
© 1999, Cisco Systems, Inc.
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MPLS Labels
Two types of MPLS Labels:
Prefix Labels & Tunnel Labels
Distributed
by:
LDP
RSVP
MP-BGP
CR-LDP
PIM
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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
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LSP tunnel Setup
© 1999, Cisco Systems, Inc.
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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
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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.
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LSP Setup
• Initiated at the head-end of a trunk
• Uses RSVP (with extensions) to
establish Label Switched Paths
(LSPs) for traffic trunks
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Path Setup - Example
R9
R8
R3
R4
R2
Pop
R5
R1
Label 32
Label 49
Label 17
R6
R7
Label 22
Setup: Path (ERO = R1->R2->R6->R7->R4->R9)
Reply: Resv communicates labels and
reserves bandwidth on each link
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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Path Setup - more details
R1
2
1
R2
R3
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)
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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
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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”
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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
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Path Re-Optimization
• Looks for opportunities to re-optimize
– make before break
– no double counting of reservations
– via RSVP “shared explicit” style!
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Non-disruptive rerouting - new
path setup
R9
R8
R3
R4
R2
Pop
R5
R1
32
49
17
R6
R7
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
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Non-disruptive rerouting switching paths
R9
R8
R3
R4
R2
Pop
Pop
26
89
R5
R1
32
38
49
17
R6
R7
22
Resv: allocates labels for both paths
Reserves bandwidth once per link
PathTear can then be sent to remove old path (and release
resources)
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Reroute - More Details
ERO (R2-1, R3-1)
Sender_Template(R1-lo0, 00)
Session(R3-lo0, 0, R1-lo0)
00
R1 2
R3
1 R2 2
01
1
3 01
3
01
Resource Sharing
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ERO (R2-1, …, R3-3)
Sender_Template(R1-lo0, 01)
72
Reroute - More Details
R1
2
1
R2
R3
2
3
1
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)
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Reroute - More Details
R1
2
1
R2
R3
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)
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Reroute - More Details
R1
2
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1
R2
R3
3
3
75
Reroute - More Details
R1
2
1
R2
R3
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)
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Reroute - More Details
R1
2
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1
R2
R3
3
3
77
Reroute - More Details
R1
2
1
R2
R3
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)
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Reroute - More Details
R1
2
1
R2
R3
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)
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Fast Restoration
Handling link failures - two
complementary mechanisms:
• Path protection
• Link/Node protection
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Path Protection
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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
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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).
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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)
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Fast ReRoute
(aka Link Protection)
An Overview
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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)
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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
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Static backup Tunnel
R9
R8
R4
R2
R5
R1
Pop
17
R6
R7
22
Setup: Path (R2->R6->R7->R4)
Labels Established on Resv message
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Routing prior R2-R4 link failure
R9
R8
R4
R2
Pop
R1
R5
14
37
R6
R7
Setup: Path (R1->R2->R4->R9)
Labels Established on Resv message
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Link Protection Active
R9
R8
R4
R2
R5
R1
R6
R7
On failure of link from R2 -> R4, R2 simply changes outgoing
Label Stack from 14 to <17, 14>
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Link Protection Active
R8
R9
Pop 14
Swap 37->14
Push 17
R4
R2
Push 37
R5
R1
R7
R6
Swap 17->22
Label Stack:
Pop 22
R1
R2
37
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R6
17
14
R7
22
14
R4
14
R9
None
91
Fast ReRoute
More details on Link
Protection (FRR v1)
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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
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Terminology
R9
R8
R4
R2
R5
R1
R6
R7
• 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
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Terminology
• Link Protection
– In the event of a link failure, an LSP is
rerouted to the next-hop using a
preconfigured backup tunnel
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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.
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How to setup the backup tunnel?
• Just as a normal tunnel whose headend 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
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ip explicit-path name
backuppath1 enable
next-address R6
next-address R7
next-address R4
97
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 fastreroute tunnels)
• int tunnel 1
## config on the head-end
tunnel mpls traffic-eng fast-reroute
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Global Label Allocation
POP
R8
14
R9
R4
R2
R5
R1
R6
R7
• 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
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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
– < 1ms
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Path state while Rerouting
Path (…, PHOP=R2, …)
R8
BackUP tunnel
R9
Path
state
R4
R2
R5
R1
R6
R7
PathError (Reservation in Place)
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Path & Resv Msgs [Error & Tear]
R2
R1
R4
R3
When no link protection:
Resv Tear
Conf.
Path Tear
Conf.
Resv Tear
When link protection:
Path Error
Resv in
place
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R4 waits for
refresh
102
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
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Why the Patherror?
• 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
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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!
R9
R8
Resv
state
BackUP tunnel
R4
R2
R5
R1
Resv
R6
R7
• 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
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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
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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
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Fast ReRoute
Node Protection
© 1999, Cisco Systems, Inc.
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Overview
R9
R8
R4
R3
R2
R5
R1
R7
R6
Backup Tunnel to the next-hop of the LSP’s
next-hop
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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
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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
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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
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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)
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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.
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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)
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A possible solution
RP
LC
RP
LC
...
LC
• Keepalives between LC’s
• Keepalives between a LC and its master RP
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Assigning traffic to Paths
(aka autoroute)
© 1999, Cisco Systems, Inc.
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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.
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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
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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 nexthops
• 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.
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Other TE New Features
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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>
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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)
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Example
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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
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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
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Example
In-Prog Bw: 55
10
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
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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)!
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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.
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Under/Overbook
A’s config:
int s0
bandwidth <B1>
ip rsvp bandwdith <B2>
(eg 1500 kbps)
(eg 4000 kbps)
...
A
Physical T1
s0
B
...
• 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 }
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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
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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]
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QoS and RRR
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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)
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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
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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
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RSVP
LSP Signalling Protocol
for Traffic Engineering
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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)
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Why RSVP ?
• What is needed: An IP signalling Protocol!
– 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
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Do I need RSVP only for TE ?
NO !
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)
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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
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RSVP is a natural choice
• 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
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RSVP is a natural choice
• 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
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RSVP is a natural choice
• 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 rerouting sub-optimal routes
• Extensible via definition of new objects
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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-tunnelapplicability-01.txt)
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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
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TE/RSVP Scalability
• With basic RSVP (RFC2205), 10000 RRR LSP
tunnels flowing through a 75x0 or 12000 is not a
problem
• Already Deployed on a number of Tier-1 ISP
backbones
– http://www.nanog.org/mtg-9905/hanna.html
– Ship with 12.0(5)S
• Refresh Aggregation work will again enhance this
scalability
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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
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
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Summary
© 1999, Cisco Systems, Inc.
149
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
NANOG18 - Robert Raszuk
© 2000, Cisco Systems, Inc.
150
Presentation_ID
© 1999, Cisco Systems, Inc.
151