virtual circuit switching and mplscse.iitkgp.ac.in/~sandipc/courses/cs60008/mpls.pdf · virtual...
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Virtual Circuit Switching and MPLS
Sandip Chakraborty
Department of Computer Science and Engineering,
INDIAN INSTITUTE OF TECHNOLOGY KHARAGPUR
February 4, 2016
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 0 / 18
Virtual Circuit Switching
Advantages and disadvantages for packet switching and circuitswitching
Virtual circuit switching - circuit switching over packet switchednetworks (PSN)
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 1 / 18
Virtual Circuit Switching
Advantages and disadvantages for packet switching and circuitswitching
Virtual circuit switching - circuit switching over packet switchednetworks (PSN)
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 2 / 18
Virtual Circuit Switching - Advantages
Packets are delivered in order, since they all take the same route
The overhead in the packets is smaller, since there is no need for eachpacket to contain the full address;
The connection is more reliable, network resources are allocated atcall setup so that even during times of congestion, provided that acall has been setup, the subsequent packets should get through;
Traffic engineering - QoS implementation becomes easier - now youcan implement RSVP over the virtucal circuit switched path!
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 3 / 18
Virtual Circuit Switching - Connection Establishment
Virtual Circuit Identifier (VCI)
VCI directs the path for forwarding
I1
I2
I3
I4
VCI = 2
VCI IF_IN
2
IF_OUT
I2 I4
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 4 / 18
Multiprotocol Label Switching (MPLS)
In a traditional IP network
Each router performs an IP lookup (routing), determines a next-hopbased on its routing table, and forwards the packet to that next-hop
Rinse and repeat for every router, each making its own independentrouting decisions, until the final destination is reached
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 5 / 18
Multiprotocol Label Switching (MPLS)
MPLS follows “Label Switching”, where
The first device does a routing lookup, but instead of finding anext-hop, it finds the final destination router
It finds out a pre-determined path from itself to that final router.
The router applies a “label” (or “shim”) based on this information.(VCI is now the “label”)
Future routers use the label to route the traffic without needing toperform any additional IP lookups
At the final destination router the label is removed and the packet isdelivered via normal IP routing
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 6 / 18
Advantages of Label Switching
Originally MPLS was designed to reduce IP lookups. (IP lookupoverheads associated with CIDR, longest prefix match)
Label switching reduces IP lookups - the idea was to have only thefirst router do an IP lookup, then all future routes in the networkcould do exact match “switching” based on a label.
Modern circuits can executes hundreds of IP lookups very fast, sowhy do people still care about MPLS?
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 7 / 18
Advantages of Label Switching
Implementing Traffic-Engineering - The ability to control whereand how traffic is routed on your network, to manage capacity,prioritize different services, and prevent congestion
Implementing Multi-Service Networks - The ability to deliver datatransport services, as well as IP routing services, across the samepacket-switched network infrastructure
Improving network resiliency with MPLS “Fast Reroute”.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 8 / 18
How MPLS Works?
MPLS Label Switched Path (“LSP”)One of the most important concepts for the actual use of MPLS.
Essentially a unidirectional tunnel between a pair of routers, routedacross an MPLS network
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 9 / 18
How MPLS Works?
MPLS routers -Label Edge Router (“LER”) or “ingress node” - The router whichfirst encapsulates a packet inside an MPLS LSP
Label Switching Router (“LSR”) or “transit node” - A routerwhich only does MPLS switching in the middle of an LSP
Egress Node - The final router at the end of an LSP, which removesthe label
LER
LSR
LSR
LSR
Egress
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 10 / 18
How MPLS Works?
Forward Equivalence Classes (FEC)A single flow or a group of traffic flows that follow same same LSP
Requires same level of QoS - can be grouped together
Associated with each FEC is a traffic characterization that defines QoSrequirements for that flow/group of flows.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 11 / 18
How MPLS Works?
Source: MPLS by William Stallings, The Internet Protocol Journal
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 12 / 18
How MPLS Works?
Prior to routing and delivery of packets in a given FEC, the LSP mustbe defined. For this purpose, two protocols are used to exchangenecessary information among the routers;
An interior routing protocol, such as OSPF, is used to exchangereachability and routing information.
Labels must be assigned to the packets for a particular FEC - LabelDistribution Protocol (LDP)
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 13 / 18
How MPLS Works? - LDP
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 14 / 18
How MPLS Works? - LDP
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 15 / 18
How MPLS Works?
Source: MPLS by William Stallings, The Internet Protocol Journal
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 16 / 18
Key Features of MPLS
An MPLS domain consists of a contiguous, or connected set of MPLSenabled routers - we can implement virtual private network (VPN)using MPLS.
The FEC for a packet can be determined by one or more parameters,like source and destination IP address, source and destination portnumbers, IP protocol ID, differentiated service code point, IPv6 flowlabel
Forwarding is achieved by doing a simple lookup in a predefined tablethat maps label values to next hop addresses.
A particular Per-Hop Behavior (PHB) can be defined at an LSR for agtiven FEC.
Packets sent between the same endpoints may belong to differentFECs. Example: VoIP packets and VoD packets.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 17 / 18
Key Features of MPLS
An MPLS domain consists of a contiguous, or connected set of MPLSenabled routers - we can implement virtual private network (VPN)using MPLS.
The FEC for a packet can be determined by one or more parameters,like source and destination IP address, source and destination portnumbers, IP protocol ID, differentiated service code point, IPv6 flowlabel
Forwarding is achieved by doing a simple lookup in a predefined tablethat maps label values to next hop addresses.
A particular Per-Hop Behavior (PHB) can be defined at an LSR for agtiven FEC.
Packets sent between the same endpoints may belong to differentFECs. Example: VoIP packets and VoD packets.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 17 / 18
Key Features of MPLS
An MPLS domain consists of a contiguous, or connected set of MPLSenabled routers - we can implement virtual private network (VPN)using MPLS.
The FEC for a packet can be determined by one or more parameters,like source and destination IP address, source and destination portnumbers, IP protocol ID, differentiated service code point, IPv6 flowlabel
Forwarding is achieved by doing a simple lookup in a predefined tablethat maps label values to next hop addresses.
A particular Per-Hop Behavior (PHB) can be defined at an LSR for agtiven FEC.
Packets sent between the same endpoints may belong to differentFECs. Example: VoIP packets and VoD packets.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 17 / 18
Key Features of MPLS
An MPLS domain consists of a contiguous, or connected set of MPLSenabled routers - we can implement virtual private network (VPN)using MPLS.
The FEC for a packet can be determined by one or more parameters,like source and destination IP address, source and destination portnumbers, IP protocol ID, differentiated service code point, IPv6 flowlabel
Forwarding is achieved by doing a simple lookup in a predefined tablethat maps label values to next hop addresses.
A particular Per-Hop Behavior (PHB) can be defined at an LSR for agtiven FEC.
Packets sent between the same endpoints may belong to differentFECs. Example: VoIP packets and VoD packets.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 17 / 18
Key Features of MPLS
An MPLS domain consists of a contiguous, or connected set of MPLSenabled routers - we can implement virtual private network (VPN)using MPLS.
The FEC for a packet can be determined by one or more parameters,like source and destination IP address, source and destination portnumbers, IP protocol ID, differentiated service code point, IPv6 flowlabel
Forwarding is achieved by doing a simple lookup in a predefined tablethat maps label values to next hop addresses.
A particular Per-Hop Behavior (PHB) can be defined at an LSR for agtiven FEC.
Packets sent between the same endpoints may belong to differentFECs. Example: VoIP packets and VoD packets.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 17 / 18
Acknowledgements
Wiki documents
MPLS for Dummies - Richard A Steenbergen, nLayerCommunications, Inc, https:
//www.nanog.org/meetings/nanog49/presentations/Sunday/mpls-nanog49.pdf
Related documents and white-papers from the Internet.
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 18 / 18
Thank You
Sandip Chakraborty (IIT Kharagpur) CS 60008 February 4, 2016 18 / 18