Transcript MPLS QoS - Lyle School of Engineering

Lecture 9
Mark E. Allen
SMU 8344
SMU
CSE 8344
Agenda
• Summarize MPLS
– Discussion from Cisco Presentation
• Discuss QoS in MPLS
– Chapter 6 in MPLS Book
• Traffic Engineering in MPLS
– Chapter 7 MPLS Book
• Virtual Private Networks
– Chapter 8 MPLS Book
• Introduction to Optical Networking
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MPLS Architecture
Overview
Adapted from Stefano Previdi’s and Jay Kumarasamy
presentation
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Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Day in the Life of a Packet
CSE 8344
MPLS Concepts
•
•
•
•
MPLS: Multi Protocol Label Switching
MPLS is a layer 2+ switching
Developed to integrate IP and ATM
MPLS forwarding is done in the same
way as in ATM switches
• Packet forwarding is done based on
Labels
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MPLS Concepts
• Unlike IP, classification/label can be based
on:
Destination Unicast address
Traffic Engineering
VPN
QoS
• FEC: Forwarding Equivalence Class
• A FEC can represent a: Destination address
prefix, VPN, Traffic Engineering tunnel, Class
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of Service.
Agenda
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Summary
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LSRs and Labels
• LSR: Label Switch Router
• Edge-LSR: LSRs that do label
imposition and disposition
• ATM-LSR: An ATM switch with Label
Switch Controller
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LSRs and Labels
IGP domain with a label
distribution protocol
• An IP routing protocol is used within the routing domain
(e.g.:OSPF, i-ISIS)
• A label distribution protocol is used to distribute address/label
mappings between adjacent neighbors
• The ingress LSR receives IP packets, performs packet
classification, assign a label, and forward the labelled packet into
the MPLS network
•
Core LSRs switch packets/cells based on the label value
•
The egress LSR removes the label before forwarding the
IP packet outside the MPLS network
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LSRs and Labels
0
1
2
3
01234567890123456789012345678901
Label
| Exp|S|
TTL
Label = 20 bits
Exp = Experimental, 3 bits
S = Bottom of stack, 1bit
TTL = Time to live, 8 bits
• Uses new Ethertypes/PPP PIDs/SNAP values/etc
• More than one Label is allowed -> Label Stack
• MPLS LSRs always forward packets based on the
value of the label at the top of the stack
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LSRs and Labels
PPP Header(Packet over
SONET/SDH)
Ethernet
Frame Relay
ATM Cell Header
GFC
PPP Header
Shim Header
Layer 3 Header
Ethernet Hdr
Shim Header
Layer 3 Header
FR Hdr
Shim Header
Layer 3 Header
VPI
VCI
PTI CLP HEC
DATA
VCI
PTI CLP HEC
DATA
Label
Subsequent cells GFC
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VPI
Label
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Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Day in the Life of a Packet
CSE 8344
Label Assignment and
Distribution
• Labels have link-local significance
Each LSR binds his own label mappings
• Each LSR assign labels to his FECs
• Labels are assigned and exchanged between
adjacent neighboring LSR
• Applications may require non-adjacent
neighbors
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Label Assignment and
Distribution
Upstream and Downstream LSRs
171.68.40/24
171.68.10/24
Rtr-A
Rtr-B
Rtr-C
• Rtr-C is the downstream neighbor of Rtr-B for
destination 171.68.10/24
• Rtr-B is the downstream neighbor of Rtr-A for
destination 171.68.10/24
• LSRs know their downstream neighbors through the IP
routing protocol
–
Next-hop address is the downstream neighbor
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Label Assignment and
Distribution
Unsolicited Downstream Distribution
Use label 30 for destination
171.68.10/24
Use label 40 for destination
171.68.10/24
171.68.40/24
171.68.10/24
Rtr-A
Rtr-B
Rtr-C
In
I/F
In
Lab
Address
Prefix
Out
I/F
Out
Lab
In
I/F
In
Lab
0
-
171.68.10
1
0
30 171.68.10
...
...
30
...
...
...
Next-Hop...
...
Address
Prefix
Out
I/F
Out
Lab
1
40
...
Next-Hop...
...
IGP derived routes
In
I/F
In
Lab
Address
Prefix
0
40 171.68.10
...
...
Out
I/F
Out
Lab
1
...
Next-Hop...
...
• LSRs distribute labels to the upstream neighbors
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Label Assignment and
Distribution
On-Demand Downstream Distribution
Use label 40 for destination
171.68.10/24
Use label 30 for destination
171.68.10/24
171.68.10/24
171.68.40/24 Rtr-A
Rtr-B
Request label for
destination 171.68.10/24
Rtr-C
Request label for
destination 171.68.10/24
• Upstream LSRs request labels to downstream neighbors
• Downstream LSRs distribute labels upon request
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Label Assignment and
Distribution
Label Retention Modes
• Liberal retention mode
• LSR retains labels from all neighbors
Improve convergence time, when next-hop is again available
after IP convergence
Require more memory and label space
• Conservative retention mode
• LSR retains labels only from next-hops neighbors
LSR discards all labels for FECs without next-hop
Free memory and label space
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Label Assignment and
Distribution
Label Distribution Modes
• Independent LSP control
LSR binds a Label to a FEC independently, whether or not the LSR has
received a Label the next-hop for the FEC
The LSR then advertises the Label to its neighbor
• Ordered LSP control
LSR only binds and advertise a label for a particular FEC if:
it is the egress LSR for that FEC or
it has already received a label binding from its next-hop
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Label Assignment and
Distribution
Several protocols for label exchange
• LDP
Maps unicast IP destinations into labels
• RSVP, CR-LDP
Used in traffic engineering
• BGP
External labels (VPN)
• PIM
For multicast states label mapping
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Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Day in the Life of a Packet
CSE 8344
Label Switch Path (LSP)
IGP domain with a label
distribution protocol
IGP domain with a label
distribution protocol
LSP follows IGP shortest path
LSP diverges from IGP shortest path
• LSPs are derived from IGP routing information
• LSPs may diverge from IGP shortest path
LSP tunnels (explicit routing) with TE
• LSPs are unidirectional
Return traffic takes another LSP
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Label Switch Path (LSP)
Penultimate Hop Popping
• The label at the top of the stack is removed
(popped) by the upstream neighbor of the
egress LSR
• The egress LSR requests the “popping”
through the label distribution protocol
•Egress LSR advertises implicit-null label
• The egress LSR will not have to do a lookup
and remove itself the label
•One lookup is saved in the egress LSR
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Label Switch Path (LSP)
Penultimate Hop Popping
In
I/F
0
In
Lab
-
...
...
Address
Prefix
171.68/16
Out
I/F
1
Next-Hop
...
...
Out
Lab
4
In
I/F
0
In
Lab
4
...
...
...
Address
Prefix
171.68/16
Out
I/F
2
Next-Hop
...
...
Summary route
for 171.68/16
0
1
1
Out
Lab
pop
Address
Prefix and mask
Next-Hop
Interface
171.68.10/24
171.68.9.1
Serial1
171.68.44/24
171.68.12.1
Serial2
171.68/16
...
Null
...
Summary route
for 171.68/16
0
171.68.44/24
Use label 4 for
FEC 171.68/16
Use label “implicit-null”
for FEC 171.68/16
171.68.10/24
Egress LSR summarises more
specific routes and advertises
a label for the new FEC
Summary route is propagate through
the IGP and label is assigned by each
LSR
Egress LSR needs to do an IP lookup for finding more
specific route
Egress LSR need NOT receive a labelled packet
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Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Summary
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ATM LSRs
• ATM switches forward cells, not packets
• Label Dist is Downstream on-demand, Ordered
• IGP label is carried in the VPI/VCI field
• Merging LSR:
Ability to use the same label for different FECs if outgoing
interface is the same
Save label space on ATM-LSRs
Cell interleave problem
• Non Merging LSR:
ATM-LSR requests one label per FEC and per incoming interface
(upstream neighbors)
Downstream LSR may request itself new label to its downstream
neighbors
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ATM LSRs
Non-Merging Downstream on
Demand
In
In Address
I/F Lab
Prefix
Out Out
I/F Lab
1
5
171.68
0
3
2
8
171.68
0
4
...
...
...
...
...
ATM-LSR requested additional label
for same FEC in order to distinguish
between incoming interfaces
(Downstream on Demand)
5
IP
Packet
ATM
cell
5
ATM
cell
IP
Packet
8
ATM
cell
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8
ATM
cell
8
ATM
cell
4
3
4
3
4
ATM
cell
ATM
cell
ATM
cell
ATM
cell
ATM
cell
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171.68
ATM LSRs
VC-Merging Downstream on
Demand
In
In Address
I/F Lab
Prefix
Out Out
I/F Lab
1
5
171.68
0
3
2
8
171.68
0
3
...
...
...
...
...
ATM-LSR transmitted cells in sequence
in order for the downstream LSR to
re-assembling correctly the cells into
packets
5
IP
Packet
ATM
cell
5
ATM
cell
IP
Packet
8
ATM
cell
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8
ATM
cell
8
ATM
cell
3
3
3
3
3
ATM
cell
ATM
cell
ATM
cell
ATM
cell
ATM
cell
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171.68
Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Summary
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Loops and TTL
• In IP networks TTL is used to prevent packets
to travel indefinitely in the network
• MPLS may use same mechanism as IP, but not
on all encapsulations
• TTL is present in the label header for PPP and LAN
headers (shim headers)
• ATM cell header does not have TTL
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Loops and TTL
• LSRs using ATM do not have TTL capability
• Some suggested options:
- hop-count object in LDP
- Path Vector object in LDP
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Loops and TTL
LSR-1
LSR3
LSR-2
IP packet
TTL = 10
Label = 25
IP packet
TTL = 6
Label = 39
IP packet
TTL = 6
LSR-6
LSR-6 --> 25
Hops=4
IGP domain with a label
distribution protocol
Label = 21
IP packet
TTL = 6
IP packet
TTL = 6
Egress
LSR-5
LSR-4
• TTL is decremented prior to enter the non-TTL capable LSP
If TTL is 0 the packet is discarded at the ingress point
• TTL is examined at the LSP exit
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Agenda
SMU
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Day in the Life of a Packet
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LDP Concepts
• Label Distribution Protocol
• Labels map to FECs for Unicast Destination
Prefix
• LDP works between adjacent/non-adjacent
peers
• LDP sessions are established between peers
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LDP Messages
• Discovery messages
• Used to discover and maintain the presence of
new peers
• Hello packets (UDP) sent to all-routers multicast
address
• Once neighbor is discovered, the LDP session is
established over TCP
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LDP Messages
• Session messages
• Establish, maintain and terminate LDP sessions
• Advertisement messages
• Create, modify, delete label mappings
• Notification messages
• Error signalling
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Agenda
•
MPLS Concepts
•
LSRs and labels
•
Label assignment and distribution
•
Label Switch Paths
•
ATM LSRs
•
Loops and TTL
•
LDP overview
•
Day in the Life of a Packet
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Day in the life of a Packet
In
I/F
0
In
Lab
-
...
...
Address
Prefix
171.68/16
Out
I/F
1
Next-Hop
...
...
Out
Lab
4
In
I/F
0
In
Lab
4
...
...
...
Address
Prefix
171.68/16
Out
I/F
1
Next-Hop
...
...
Out
Lab
7
In
I/F
0
In
Lab
7
...
...
...
P1
1
PE
P
0
0
Use label 4 for
FEC 171.68/16
0
Use label 7 for
FEC 171.68/16
Summary route
for 171.68/16
CE
Address
Prefix
171.68/16
Out
I/F
2
Next-Hop
...
...
Out
Lab
pop
...
Address
Prefix and mask
Next-Hop
Interface
171.68.10/24
171.68.9.1
Serial1
171.68.44/24
171.68.12.1
Serial2
171.68/16
...
Null
2
0
PE
Use label “implicit-null”
for FEC 171.68/16
Summary route
for 171.68/16
171.68.44/24
171.68.10/24
Summary route is propagate through
the IGP and label is assigned by each
LSR
Egress LSR summarises more
specific routes and advertises
a label for the new FEC
Egress LSR needs to do an IP lookup for finding more specific route
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Day in the life of a Packet Basic
Layout
Control Plane
IP Routing Protocols
Routing Exchange
IP Routing Table
Label Distribution Protocol
Label Binding Exchange
Label Removed
L3 lookup
Outgoing IP Packets
Incoming IP Packets
Forward Information Block (FIB)
Incoming LabelledPackets
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Label Forward Information Block
(LFIB)
Forwarding Plane
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Outgoing Labelled Packets
Day in the life of a Packet
Database Layout
ISIS
OSPF
BGP
LDP
Routing Table
ge
han
fasttag-rewrite
tag_info
rou
t
e-ta
tag_rewrite [ ]
tag_hash
fast-adjacency
g-c
incoming-tag
find
-ro
ute
req
- ta
_al
l_ta g
gs
FIB
TIB
Dest. IP address
tag_rewrite
output-if
encaps
incoming-tag
outgoing-tag
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IDB vectors
TFIB
tfib_entry
tag_rewrite
loadinfo
tag_info
Incoming tag
tfib_entry
tfib_entry
tfib_entry
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ip_turbo_fs
tag_optimum_fs
ip2_tag_optimum_fs
DISCUSSION OF QoS and
Constraint Based Routing
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Key Questions
• How does MPLS Support QoS?
• What is the difference between
Integrated Services (INT-SERV)
Differentiated Services (DIFFSERV)?
– Integrated services
• T-Spec and R-Spec
• Much of this is similar to ATM
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Integrated Services
• An attempt to bring the ATM capabilities to IP
– T-Spec: Max burst size, token rate, committed rate, etc.
– R-Spec: Effective bandwidth or amount of resource
required within the network.
• This is very different than “best-effort” and
requires sophisticated queuing mechanisms
• Many in the industry saw this as a “reinvention” of
ATM
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Integrated Services
• architecture for providing QOS
guarantees in IP networks for individual
application sessions
• resource reservation: routers maintain
state info of allocated resources
• admit/deny new call setup requests:
Question: can newly arriving flow be admitted
with performance guarantees while not violated
QoS guarantees made to already admitted flows?
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Intserv: QoS guarantee
scenario
• Resource reservation
– call setup, signaling (RSVP)
– traffic, QoS declaration
– per-element admission control
request/
reply
– QoS-sensitive
scheduling
(e.g., WFQ)
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Call Admission
Arriving session must :
• declare its QOS requirement
– R-spec: defines the QOS being requested
• characterize traffic it will send into network
– T-spec: defines traffic characteristics
• signaling protocol: needed to carry R-spec and Tspec to routers (where reservation is required)
– RSVP
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Intserv QoS: Service models
[rfc2211, rfc2212]
Guaranteed service:
• worst case traffic
arrival: leaky-bucketpoliced source
arriving
traffic
token rate, r
bucket size, b
WFQ
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Controlled load
service:
• "a quality of service
closely approximating
the QoS that same flow
would receive from an
unloaded network
element."
per-flow
rate, R
D = b/R
max
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IETF Differentiated Services
Concerns with Intserv:
• Scalability: signaling, maintaining per-flow router
state difficult with large number of flows
• Flexible Service Models: Intserv has only two
classes. Also want “qualitative” service classes
– “behaves like a wire”
– relative service distinction: Platinum, Gold, Silver
Diffserv approach:
• simple functions in network core, relatively
complex functions at edge routers (or hosts)
• Don’t define service classes, provide functional
components to build service classes
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Diffserv Architecture
r
Edge router:
- per-flow traffic management
- marks packets as in-profile
and out-profile
Core router:
- per class traffic management
- buffering and scheduling
based on marking at edge
- preference given to in-profile
packets
- Assured Forwarding
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b
marking
scheduling
..
.
Edge-router Packet Marking
• profile: pre-negotiated rate A, bucket size B
• packet marking at edge based on per-flow profile
Rate A
B
User packets
Possible usage of marking:
• class-based marking: packets of different classes
marked differently
• intra-class marking: conforming portion of flow
marked differently than non-conforming one
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Classification and
Conditioning
• Packet is marked in the Type of Service (TOS) in
IPv4, and Traffic Class in IPv6
• 6 bits used for Differentiated Service Code Point
(DSCP) and determine PHB that the packet will
receive
• 2 bits are currently unused
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Classification and
Conditioning
may be desirable to limit traffic injection rate of
some class:
• user declares traffic profile (egs., rate, burst
size)
• traffic metered, shaped if non-conforming
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Forwarding (PHB)
• Per Hop Behavior (PHB)
• PHB result in a different observable (measurable)
forwarding performance behavior
• PHB does not specify what mechanisms to use to
ensure required PHB performance behavior
• Examples:
– Class A gets x% of outgoing link bandwidth over time
intervals of a specified length
– Class A packets leave first before packets from class B
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Forwarding (PHB)
PHBs being developed:
• Expedited Forwarding: pkt departure rate
of a class equals or exceeds specified rate
– logical link with a minimum guaranteed rate
• Assured Forwarding: 4 classes of traffic
– each guaranteed minimum amount of bandwidth
– each with three drop preference partitions
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Summary
• REFER TO MPLS 8 LECTURE
FOR More Detail on these QoS and
CBR (Constraint Based Routing)
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Virtual Private Networks
(VPNs)
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When VPN?
• Internet as your own private network
– Communicate securely between various
corporate sites (Intranet)
– Communicate securely between partner
sites (Extranet)
– Connect remote dial-up users securely to
corporate networks
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Advantages
• Flexible and cost effective
• Better business-to-business
connectivity
– business partners, service providers,
contractors, and customers
• Advances in security
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Layer2 vs. Layer3 VPNs
Layer 3 VPNs
Layer 2 VPNs
•Provider devices forward
customer packets based on
Layer 3 information (e.g., IP)
•Provider devices forward
customer packets based on
Layer 2 information
•SP involvement in routing
•Tunnels, circuits, LSPs, MAC
address
•MPLS/BGP VPNs (RFC
2547), GRE, virtual router
approaches
•“pseudo-wire” concept
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Layer2 Example
Step #1
Workstation A
sends packet
destined for
Server B
Step #2 R1 takes
Ethernet frame and
encapsulates it in L2TP
and routes it to tunnel
destination
IP Core
R1
Ethernet
IP or MPLS
Core
IP L2TP Ethernet
L2TPv3 Tunnel
Workstation A
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Step #3 R2 receives
IP/L2TP/Ethernet
Packet and removes
the IP/L2TPv3 headers.
The remaining Ethernet
frame is forwarded to
Server B.
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R2
Ethernet
Overlay Model
• Each site has a router connected via
P-T-P links to routers on other sites
– Leased lines
– Frame relay
– ATM circuit
• Connectivity
– Fully connected
– Hub-and-spoke
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Limitations of Overlay
• Customers need to manage the backbones
• Mapping between Layer2 Qos and IP
QoS
• Scaling problems
– Cannot support large number of
customers
– (n-1) peering requirement
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The Peer Model
• Aims to support large-scale VPN
service
• Key technologies
–
–
–
–
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Constrained distribution of routing info.
Multiple forwarding tables
VPN-IP addresses
MPLS switching
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Terminology
• CE router
• Customer Edge router
• PE router
– Provider Edge router. Part of the PNetwork and interfaces to CE routers
• P router
– Provider (core) router, without
knowledge of VPN
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Terminology (cont’d)
• Route Distinguisher
• Attributes of each route used to uniquely
identify prefixes among VPNs (64 bits)
• VPN-IPv4 addresses
• Address including the 64 bits Route
Distinguisher and the 32 bits IP address
• VRF
– VPN Routing and Forwarding Instance
– Routing table and FIB table
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Connection Model
• The VPN backbone is composed by MPLS
LSRs
• PE routers (edge LSRs)
• P routers (core LSRs)
• PE routers are faced to CE routers and
distribute VPN information through BGP to
other PE routers
• P routers do not run BGP and do not have
any VPN knowledge
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Model (cont’d)
• P and PE routers share a common IGP
• PE and CE routers exchange routing
information through:
• EBGP, OSPF, RIP, Static routing
• CE router run standard routing
software
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Routing
• The routes the PE receives from CE
routers are installed in the appropriate
VRF
• The routes the PE receives through the
backbone IGP are installed in the global
routing table
• By using separate VRFs, addresses need
NOT to be unique among VPNs
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Forwarding
• PE and P routers have BGP next-hop
reachability through the backbone IGP
• Labels are distributed through LDP (hopby-hop) corresponding to BGP Next-Hops
• Label Stack is used for packet forwarding
• Top label indicates Next-Hop (interior
label)
• Second level label indicates outgoing
interface or VRF (exterior label)
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Forwarding (cont’d)
• The upstream LDP peer of the BGP nexthop (PE router) will pop the first level label
• The egress PE router will forward the
packet based on the second level label
which gives the outgoing interface (and
VPN)
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Forwarding Example
CE1
IP
packet
P routers switch the
packets based on the IGP
label (label on top of the
stack)
PE1
Penultimate Hop
Popping
P2 is the penultimate
hop for the BGP nexthop
P2 remove the top label
This has been
requested through LDP
by PE2
PE2 receives the packets
with the label
corresponding to the
outgoing interface (VRF)
One single lookup
Label is popped and packet
sent to IP neighbour
CE2
IGP
Label(PE2)
VPN
IP Label
IP
packet
packet
PE1 receives IP packet
Lookup is done on site VRF
BGP route with Next-Hop and
Label is found
BGP next-hop (PE2) is reachable
through IGP route with
associated label
SMU
P1
IGP
Label(PE2)
VPN
IP Label
packet
VPN Label
P2
IP
packet
PE2
CE3
CSE 8344
Scalability
• Existing BGP techniques can be used to
scale the route distribution
• Each edge router needs only the
information for the VPNs it supports
• Directly connected VPNs
• Easy to add new sites
– configure the site on the PE connected to it,
the network automatically does the rest
SMU
CSE 8344
QoS Support
• Pipe model
– Similar to int-serv
• Hose Model
– Similar to diff-serv
SMU
CSE 8344