Download COS 420 day 16

COS 420
Day 16
Agenda

Assignment 3 Corrected



Assignment 4 Posted



Chap 16-20
Due April 6
Individual Project Presentations Due


Poor results 1 C and 2 Ds
Spring Break??
MANETS - Donnie
Today we will discuss IP Switching and MPLS
Group Project Initial
Discussion

Deliverables



Programs requirements
Protocol Definition
Working Network Application



Paper






Client Server For File Sharing
Peer to Peer??
User Manual
Protocol specification
Program requirements
Implementation Technical Specifications
Presentation
Journal?
Project 2 Grading


Meeting Timelines
Deliverables




Program requirements
Protocol Definition
Working Network Application
Final Paper





10%
Due
Due
Due
Due
March 30
April 13
May 4
May 1
15%
15%
25%
25%
User Manual
Protocol
Program requirements
Technical Specifications
Presentation
Due May 4
10%
PART XVII
IP Switching and MPLS
Switching Technology



Designed as a higher-speed alternative
to packet forwarding
Uses array lookup instead of destination
address lookup
Often associated with Asynchronous
Transfer Mode (ATM)
Switching Concept



Part (b) shows table for switch S1
Identifier in packet known as label
All labels except 2 go out interface 1
Extending Switching To A
Large Network


Label replacement known as label swapping
A path through the network corresponds to a
sequence of labels
An Important Note

Switching uses a connection-oriented
approach. To avoid the need for global
agreement on the use of labels, the
technology allows a manager to define
a path of switches without requiring
that the same label be used across the
entire path.
Potential Advantages Of
Switching for IP Forwarding



Faster forwarding
Aggregated route information
Ability to manage aggregate flows
IP Switching



Pioneered by Ipsilon Corporation
Originally used ATM hardware
Variants by others known as




Layer 3 switching
Tag switching
Label switching
Ideas eventually consolidated into Multi-
Protocol Label Switching (MPLS)
MPLS Operation

Internet divided into




Standard routers
MPLS core
Datagram encapsulated when entering
the MPLS core and de-encapsulated
when leaving
Within the core, MPLS labels are used
to forward packets
Processing An Incoming
Datagram

Datagram classified




Multiple headers examined
Example: classification can depend on TCP
port numbers as well as IP addresses
Classification used to assign a label
Note: each label corresponds to ‘‘flow’’
that may include may TCP sessions
Hierarchical MPLS


Multi-level hierarchy is possible
Example: corporation with three campuses
and multiple buildings on each campus




Conventional forwarding within a building
One level of MPLS for buildings within a campus
Additional level of MPLS between campuses
To accommodate hierarchy, MPLS uses stack
of labels
MPLS Label Processing



Only top label is used to forward
When entering new level of hierarchy,
push addtional label on stack
When leaving a level of the hierarchy,
pop the top label from the stack
MPLS Encapsulation


MPLS can run over conventional
networks
Shim header contains labels
Fields In An MPLS Shim Header

Shim header



Prepended to IP datagram
Only used while datagram in MPLS core
MPLS switches use LABEL in shim when forwarding
packet
Label Switching Router (LSR)

Device that connects between
conventional Internet and MPLS core


Handles classification
Uses data structure known as Next Hop
Label Forwarding Table (NHLFT) to choose
an action
Next Hop Label Forwarding
Entry


Found in NHLFT
Specifies





Next hop information (e.g., the outgoing interface)
Operation to be performed
Encapsulation to use (optional)
How to encode the label (optional)
Other information needed to handle the packet
(optional)
Possible Operations



Replace label at top of stack
Pop label at top of stack
Replace label at top of stack, and then
push one or more new labels onto stack
Control Processing And Label
Distribution

Needed to establish Label Switched
Path (LSP)



Coordinate labels along the path
Configure next-hop forwarding in switches
Performed by Label Distribution
mechanism

Series of labels selected automatically
Protocols For MPLS Control

Two primary protocols proposed



Label Distribution Protocol (MPLS-LDP)
Constraint-Based Routing LDP (CR-LDP)
Other proposals to extend routing
protocols


OSPF
BGP
Notes About Fragmentation

Outgoing



MPLS prepends shim header to each datagram
If datagram fills network MTU, fragmentation will
be required
Incoming



Classification requires knowledge of headers (e.g.,
TCP port numbers)
Only first fragment contains needed information
LSR must collect fragments and reassemble before
classification
Mesh Topology




Used in many MPLS cores
LSP established between each pair of
LSRs
Parallel LSPs can be used for levels of
service
Example


One LSP reserved for VOIP traffic
Another LSP used for all other traffic
Service Differentiation

Because MPLS classification can use
arbitrary fields in a datagram, including
the IP source address, the service a
datagram receives can depend on the
customer sending the datagram as well
as the type of data being carried.