Multiprotocol Label Switching MPLS

1
Multiprotocol Label Switching (MPLS)

• References
• Juniper white papers on MPLS and DiffServ at
• http//www.juniper.net/solutions/literature/white_
  papers/

2
Outline

• General concepts
• ATM LSR
• Ships-in-the-night
• DiffServ-MPLS architecture
• Resource provisioning
• High availability

3
MPLS General Concepts

• Outline
• Historic perspective
• MPLS basics
• ATM LSR

4
A historical Perspective

• What happened in mid-90s?
• The problems with overlay models reveal
  themselves
• Overlay models create bottleneck from the lack of
  segmentation and reassembly (SAR) functionality
  on interfaces faster than OC-48
• Overlay models increase complexity by requiring
  providers to manage two separate control planes
  and two fundamentally different types of
  networking equipment
• Overlay model results in an inefficient use of
  network bandwidth due to the traditional ATM cell
  tax
• No QoS for LANE and the IP Diffserv approach to
  CoS does not map well to the existing ATM QoS
  mechanims
• LANE requires a client-server model in place,
  e.g., LEC, LECS, LES, and BUS
• Classical IP over ATM requires the deployment of
  n-squared routing adjacencies.

5
A Historical Perspective (contd)

• Multi-layer switching solutions in the spotlight
• IP switching by Ipsilon/Nokia
• Tag switching by Cisco
• Aggregate routing-based IP switching (ARIS) by
  IBM
• IP Navigator by Cascade/Ascend/Lucent
• Cell Switching Router (CSR) by Toshiba
• All ATM based solutions

6
MPLS Basics

• MPLS switching concept

7
MPLS Basics (contd)

• Separation of control functions from forwarding
  functions

8
MPLS Basics (contd)

• Label distribution and label swapping

9
MPLS Basics (contd)

• Generic label and label stacking

10
MPLS Basics (contd)

• ATM Based label and label stacking

0
0
VPI/VCI

LAYER-3
0
LAYER-2
1
20
3
1
8
Label
exp
s
TTL
11
MPLS Basics (contd)

• MPLS signaling protocols distribute labels and
  maintain connectivity of an LSP
• Topology driven
• LDP
• distributes labels based on routing topology,
  i.e., label to FEC binding where FEC IP prefix.
  
• Using TCP and maintaining hard state.
• No QoS.
• Policy driven
• RSVP-TE Widely deployed
• distributes labels based on source routing
• Using raw IP and maintaining soft state
• Designed for QoS
• CR-LDP not well accepted
• Distributes labels based on source routing
• Using TCP and maintaining hard state
• Designed for QoS

12
MPLS Basics (contd)

• Label distribution mechanisms
• Downstream-on-demand (RSVP-TE, CR-LDP, LDP)
• Unsolicited-downstream (LDP)

Label Request
Downstream LSR
Upstream LSR
Label Response
Next Hop to FEC
Downstream LSR
Upstream LSR
Unsolicited Label Response
Next Hop to FEC
13
MPLS Basics (contd)

• Label retention modes
• Conservative label retention
• an upstream LSR maintains the received label
  binding for an FEC only if the label binding is
  received from the downstream LSR that the
  upstream LSR has selected as the next-hop for
  that FEC
• Liberal label retention
• An upstream LSR maintains the received label
  binding for an FEC even if the label binding is
  received from a downstream LSR that the upstream
  LSR has not selected as the next-hop for that FEC
• Pros and Cons of the two modes?

14
MPLS Basics (contd)

• Routing for MPLS
• Traditional shortest path based IP routing
  protocols provide enough information for LDP
  signaling
• Policy driven signaling protocols set up an LSP
  based on the policy
• A policy may enforce a manually configured route
• A policy may use a route found by a
  constraint-based routing protocol
• A policy may use a route found by a shortest-path
  based routing protocol
• Constraint-based routing protocols
• Find best routes meeting multiple criteria
• Pre-calculate or calculate on-demand

15
MPLS Basics (contd)

• MPLS eliminates the potential for SAR
  bottlenecks by not using ATM as a transport
• MPLS eliminates the complexity of managing two
  separate control planes and two fundamentally
  different types of networking equipment.
• MPLS eliminates the cell tax by not using ATM as
  a transport
• MPLS can support DiffServ CoS.
• The peer-to-peer nature of IP routed MPLS
  eliminates the need to manage a complex logical
  topology (n-squared PVCs)
• MPLS provides flexible traffic engineering
  features

16
MPLS Related Research Topics

• MPLS multicasting
• Pseudo-wire over MPLS
• MPLS VPN
• MPLS high availability
• MPLS Traffic engineering
• Useful Resources
• Go to
• http//www3.uta.edu/library/ejournals/
• and click on
• ACM Digital Library
• IEEE Xplore