MPLS: A Packet forwarding technology for the next generation Internet Internet routing primer and cu

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MPLS A Packet forwarding technology for the
next generation InternetInternet routing primer
andcutting edge technology in only 2 hours

• Yoichi Shinoda
• Center for Information Science
• Japan Advanced Institute of
• Science and Technology

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Lecture Structure

• Internet datagram forwarding
• MPLS a new forwarding technology
• Introduction of the Ayame MPLS project

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Datagram Forwarding in the Internet

• We will learn
• How a datagram destined for a particular address
  is forwarded through the Internet.

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Forwarding and Routing

• The two major functions of the Layer 3 (network
  layer) function in the Internet are
• Forwarding
• A datagram is forwarded to an appropriate
  next-hop intermediate node (router).
• Routing
• A datagrams is eventually delivered from its
  source to destination as a result of repeated
  forwarding.

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Forwarding and Routing
S
D
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Datagram forwarding control

• What is the information requiredfor correct
  forwarding?

addr A
addr X
if0
router R
addr B
addr B
addr Y
if1
if2
A mapping ofaddr B ? (addr Y, if1)is required
addr C
addr Z
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Datagram forwarding with route table
X
if0
router R
destIP
Y
addr B
if1
datagram
table lookup (key destIP addr B)
Z
if2
Matchingentry
Route table
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Route table entry types (1) --- by source

• Static
• An entry is manually entered into the table.
• Dynamic
• An entry is learned automatically through routing
  protocols.
• Redirected
• An entry is created as a result of redirection by
  another router (suggested better route).

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Route table entry types (2) -- by route
specific-ness
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Specific-ness of routes
Entire Internet
Network W
Network V
Z
B
A
Y
X
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Longest match first rule

• When multiple entries match for an address, then
  more specific route (entries with more
  significant bits in key field) must be chosen.

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Simple lookup algorithm (1)

• // 3 x linear search
• routeTableEntry lookup(key)
• routeTableEntry e
• // Search host route
• foreach e in table
• if (e.destIP key) return(e)
• // Search network route
• foreach e in table
• if (e.destIP key netmask(destIP)) return(e)
• // Search default route
• foreach e in table
• if (e.destIP 0) return(e)

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Simple lookup algorithm (2)

• // Single linear search
• // Entries must be sorted in descending order
  of significance
• // Entries are accompanied with comparison
  mask
• // Host route all 1s
• // Network route netmask(destIP)
• // Default route all 0s
• routeTableEntry lookup(key)
• routeTableEntry e
• foreach e in table
• if (e.destIP (key e.cmpmask)) return(e)

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In the reality Network mask variations

• Subnets
• Sub-divide a networks host-ID part into set of
  fixed size subnets.
• Introduced for higher utilization of a network.
• Subnets are only recognized in the subnetted
  network.
• Variable Length Subnet Mask (VLSM)
• Subnetting with variable sized subnets.
• Supernets and Classless Inter-Domain Routing
  (CIDR)
• Aggregate multiple VLSMs beyond network-ID
  boundary to form a larger network.

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In the reality

• Route table size Todays Internet core routers
  hold 90K110K route entries.

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Binary Tree based lookup
bit 0
bit 1
Route entryfor8.0.0.0 / 2
bit 2
Rest of the tree (For bits 3 - 31)
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How fast an IP router can be?

• Forwarding capacity of an IP router heavily
  depends on the route table lookup speed.
• Assume a 1Gbps input date rate.
• Also assume an average packet (datagram) size of
  64 bytes (0.5Kbits).
• Then packet arrival rate is 2Mpps (500nsec
  arrival interval).
• Assume 1-bit tree based lookup, with average
  search depth of 20 bits.
• Then each bit must be examined in 25nsec (almost
  impossible).

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MPLS A new forwarding technology
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Requirements for the Next Generation Internet
forwarding (1)

• Characteristics for QoS support
• Low latency Low forwarding overhead, regardless
  of route table size (may vary from 1 to tens of
  thousands).
• Low jitter Consistent forwarding overhead,
  regardless of route table size (may vary from 1
  to thousands).
• Predictable and consistent transit time.
• Ability to distinguish flows or bundle of flows
  and route them through different routes (called
  traffic engineering).

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Requirements for the Next Generation Internet
forwarding (2)

• Multi-protocol capability to allow different
  protocols to pass through the Internet under the
  control of IP (the Internet as universal
  communication infrastructure).
• You name it.

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Current Approach

• Hardware assisted/implemented route lookup and
  forwarding engines.
• VERY expensive.
• Hard to incorporate new features.
• Distributed parallel forwarding engines.
• Makes expensive routers even more expensive.

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Switched inter-networking approach

• Combines advantages of layer 3 forwarding and
  layer 2 switching
• Layer 3 (network layer)
• End-to-end reachability.
• Exchange routing information.
• Control Layer 2.5 switching functions.
• Layer 2.5 (label switching layer)
• Route datagrams using simple labels.
• Use layer 2 (datalink layer) function for actual
  transmission.
• Layer 2 (datalink layer)
• Send and receive datalink frames

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Label Switching Framework
X
Label switched network
2
X
5
X
X
IngressLSR
i/f 1
i/f 1
i/f 2
destIP
EgressLSR
4
Y
Y
Y
1
Y
Dest-to-Label Mapping Table
Label Mapping Table
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A little history on switched internetworking
Policy Routing (VPN, Traffic Engineering)
ATM
l-switching
IPSwitch (Ipsilon)
CIPover ATM
MPLS
GMPLS
CSR (CellSwitchRouter)
TAG Switching
?
non-ATM (Ether, PPP, POS, )
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MPLS advantages (1) - Functionality

• Provides QoS support
• Fast, consistent forwarding.
• Provides traffic engineering support
• Different routes (LSPs) can be assigned to flows
  at ingress LSRs.
• Provides managable/flexible L1,L2,L3 pipes
  (tunnels)
• Multi-protocol support (IPv4, IPv6, 802.3
  (Ethernet), VLAN, IEEE1394)
• Different protocols are only distinguished at
  ingress and egress routers.
• Versatile/Flexible upper layer routing

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MPLS advantages (2) - Cost Performance

• Low cost of implementation
• Complex control functions are only required at
  label distribution phase, and executed once.
• Can be implemented and excuted in software with
  least impact to performance.
• Softwares can easily be updated
• Actual forwarding can be executed with simple
  hardware.
• Hardware switch for LSR is only L2-switch a
• Ingress LSRs must be intelligent and fast, but
  required only at edge of an MPLS network.

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MPLS Network Elements

• LSR Label Switching Router.
• LSP Label Switched Path.
• Ingress-LSR Entry point into an MPLS net.
• Egress-LSR Exit point from an MPLS net.
• Core-LSR ! Ingress ! Egress.
• FEC (Forwarding Equivalence Class)
• LDPs Label distribution protocols.

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FECs and Labels

• FEC (Forwarding Equivalence Class)
• Represents a class of traffic with same
  forwarding behavior within a given MPLS system.
• Examples
• Protocol
• Destination source
• Service type
• QoS parameters
• Combinations of simple metrics
• Labels are assigned to FECs

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FECs and LSPs
LSPs
Rc
Re
dest
service
ip-X
telnet
ip-X
Rf
Rd
Ri
http
ip-X
any
ip-Y
Rb
ip-Y
Rg
mac-Z
Traffic are examined (classified) for their FEC,
and routed to corresponding LSP
mac-Z
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MPLS Applications

• Hop-by-hop routed LSP
• Direct deployment of MPLS for hop-by-hop routed
  traffic.
• Explicitly routed LSP (for TE)
• Managed LSP tunnels
• Between BGP border routers
• VPNs
• Multi-path routing
• Fast re-route
• LSP trees as point-multipoint entity

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Label Distribution Example
Net-A
X
2
Lblreq(Net-B)
LSR1
LSR2
Z
Y
Net-B
3
Lblmap(Net-B, 9)
Route table (LSR1)
2
Route table(LSR2)
1
3
Label table (LSR1)
Label table (LSR2)
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Concept of Control / Data Separation
Hop-by-hoprouted path
ControlPlane(e.g. IPv4)
Controlsignalling (LDPs)
Labelinstallation
Data(Forwarding)Plane
LSP
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Multiple Control Planes Single Data Plane
Route Control
Traditional Monolithic Control / Data Architecture
Route Table
Multiple Control / Single Data Plane Architecture

Route Control
Route Control
Route Control
.

• Multi-protocol
• Multi-control within a single protocol

LabelMappingTable
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MPLS Accerelates Media Convergence

• Example VoIP application

voice
call
voice
call
voice
call
UDP
TCP
UDP
TCP
TCP
IP
IP
IP
DL
DL
MPLS
DL
MPLS
A. Call control andvoice transmissionover
traditionalTCP/UDP/IP.
B. Call control setsup an LSP for
voicetransmission overUDP/IP/MPLS.
C. Call control setsup an LSP for directvoice
transmissionover MPLS.
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The AYAME Project

• The AYAME is the open source MPLS stack,
  developed at JAIST in corporation / collaboration
  with
• The WIDE Project (testbed)
• Moon-Bear Project (QoS/CoS support)
• DISTIX Project
• http//www.ayame.org

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What AYAME project provides

• AYAME software
• MPLS core/edge LSR
• Software switch (currently) label distribution
  protocol handlers
• Publically available
• Support protocols
• LDP, CR-LDP
• Static label allocation(TE)
• RSVP (planed)
• Co-operate with COPS
• Interoperable with
• Cisco, Juniper, Hitachi, Riverstone, Furukawa,
  Fujitsu, Zebos, Unispere

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The Ayame MPLS stack structure
Policy Network Entities (COPS, etc..)
bgpd
ospfd
(RSVPd)
L3 routing (zebra)
LabelDistribution
CR-LDPd
LDPd
Label alloc,Filter/flowspecinsertion
AYAMEd
userland
NetBSD kernel
TCP/IP stack
MPLS switch code
ALTQ
Ethernet
ATM
IP tunnel
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Moonbear/Ayame collaboration

• Moon-Bear project
• QoS-enabling implementation based on COPS (Common
  Open Policy Service) and DiffServ (Differentiated
  Service) frameworks.
• Ayame provides actual datagram forwarding
  mechanism with QoS support.
• http//www.moon-bear.net

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Ayame in DISTIX project

• DISTIX (Distributed Internet eXchange) project
• National project that exploits possibility of
  MPLS-based Internet eXchange (IX).
• Several dozen participants (router vendors, ISPs
  and end-users such as contents providers).
• http//www.distix.net (in Japanese)
• Ayame is playing an important role in the
  project.
• Provides inexpensive solution.
• Quickly modifiable software.
• Ayame testbed used for advance-inter-operability
  test.

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Future Ayame related projects

• StarBED and Ayame
• StarBED is the 500 physical node (5000
  VM-simulated node) fully programmable Internet
  simulator being built next to JAIST, intended for
  used as a versatile testbed for network oriented
  products.
• Ayame is expected to be one of the first and
  heavy user of the StarBED
• MPlS and Ayame
• Ayame is planned to be used as software
  development platform for wave-length(l)based DWDM
  switching.

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End of the Show