Chapter 16. Internetwork Operation

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Internetwork Operation
1

Chapter 16. Internetwork
Operation


Routing Protocols


Integrated Services Architecture


Resource Reservation: RSVP


Differentiated Services

Internetwork Operation
2

Protocols in the Chapter

Internetwork Operation
3

Routing Protocols


Autonomous systems (AS)


An internet connected by homogeneous
routers; generally, the routers are under the
administrative control of a single entity


Interior

router protocol (IRP)


Passes routing information between routers
within an autonomous system


Exterior

router protocol (ERP)


Passes routing information between routers in
different autonomous systems

Internetwork Operation
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Routing Protocols (cont)

Internetwork Operation
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Hierarchical Routing


Hosts


Maintain sufficient routing information to forward
datagrams to other hosts or an interior gateway(s) that
is (are) attached to the same network. (
ARP
)


Interior Gateways


Maintain sufficient routing information to forward
datagrams to hosts or other interior gateways within the
same autonomous system


Exterior Gateways


Maintain sufficient routing information to forward
datagrams either to an interior gateway, if the datagram
is for the same autonomous system, or to another
exterior gateway, if it is not.

Internetwork Operation
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Border Gateway Protocol


Standardized exterior router protocol for the
Internet (BGP
-
4, RFC 1771)


Allows routers (gateways) in different autonomous
systems to cooperate in the exchange of routing
information.


Operates in terms of messages, which are sent over
TCP

connections.


Message:
Open, Update, Keepalive, Notification


3 functional procedures


Neighbor acquisition
,
Neighbor reachability


Network reachability (Routing update)

Internetwork Operation
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BGP (cont)


Neighbor acquisition


Neighbor acquisition occurs when two
neighboring routers in different autonomous
systems agree to regularly exchange routing
information


1. One router sends an
Open

msg to another


2. If the target router accepts the request, it
returns a
Keepalive

msg in response

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BGP (cont)

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BGP (cont)


Neighbor reachability


Used to maintain the neighbor relationship


Two routers periodically issue
Keepalive

msg to
each other


Network reachability


Each router maintains a database of the
subnetworks that it can reach and the preferred
route for reaching that subnetwork


Whenever a change is made to this database,
the router issues an
Update

msg that is
broadcast to all other routers implementing
BGP

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BGP (cont)

For authentication

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BGP (cont)

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OSPF Protocol


Open Shortest Path First Protocol


Interior

routing protocol by ARPANET


Link
-
state

routing algorithm


Each router maintains descriptions of the state
of its local links to subnetworks, and from time
to time transmits updated state information to
all of the routers of which it is aware


Each router maintains a database that reflects
the known topology of the autonomous system

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OSPF Protocol (e.g.)

Sample

autonomous

system

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OSPF Protocol (e.g.)

Directed

graph of

the sample

autonomous

system

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OSPF Protocol (e.g.)

SPF tree

for

router R6

Using

Dijkstra’s

Algorithm

Internetwork Operation
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OSPF Protocol (e.g.)

Routing Table

for

router R6

Internetwork Operation
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ISA Concept


Integrated Services Architecture


Intended to provide
QoS

transport support over
IP
-
based internets,
RFC 1633


Two broad categories of traffic on internet


Elastic

Traffic


File transfer (FTP) , Email (SMTP), Remote Logon
(TELNET), Network management (SNMP), Web access
(HTTP)


Inelastic

Traffic


Real
-
time traffic


Throughput, Delay, Jitter, Packet loss

Internetwork Operation
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ISA Approach


Traditional (IP) Router mechanisms


Routing algorithm


Packet discard


ISA Enhancements: the concept of
flow


Admission control
: RSVP


Routing algorithm
: QoS
-
based OSPF


Queuing discipline
: For differing requirements
of different flow


Discard policy
: for managing congestion and
meeting QoS guarantees

Internetwork Operation
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ISA Components

ISA Implemented in Router

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2
-
Level ISA Services


1. General categories of service


Guaranteed


Assured capacity/data rate


Specified upper bound on the queuing delay


No queuing loss


Controlled Load


Best effort


2. Service for a particular flow


Traffic specification (
TSpec
):
Token Bucket


QoS

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Token Bucket Scheme

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Queuing Discipline

Weighted Fair Queuing (WFQ)

No
priority
; Larger
mean delay

Greedy TCP connections crowd

out altruistic ones

Internetwork Operation
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Resource
R
e
S
er
V
ation

P
rotocol


Characteristics


Unicast and Multicast


Simplex


Receiver
-
initiated

reservation


Maintaining
soft state

in the internet


Providing different reservation styles


Transparent operation through non
-
RSVP routers


Support for IPv4 and IPv6


Type
-
of
-
Service

in IPv4


Flow Label

in IPv6

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RSVP Design Characteristics


Receiver
-
initiated

reservation


Sender


Provide the routers with the traffic characteristics of
the transmission (data rate, variability)


Receiver


Specify the desired QoS


Router


Aggregate multicast resource reservations for the
shared path segments along the distribution tree


Soft State

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RSVP Data Flows


Flow descriptor


flowspec
: desired QoS


filterspec
: defines the set of packets for the reservation

Treatment of packets of one session at one router

Internetwork Operation
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RSVP Protocol Mechanisms


Two message types


Resv
,
Path

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Differentiated Services (DS)


Goal (RFC 2475)


Provide a simple, easy
-
to
-
implement, low
-
overhead tool to support a range of network
services (comparing with ISA)


Key characteristics


IP packets are labeled for differing QoS
treatment using the existing
IPv4

Type
-
of
-
Service

octet or
IPv6

Traffic Class

octet. Thus,
no change is required to IP

Internetwork Operation
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Differentiated Service (cont)


A
service level agreement (SLA)

is established
between the service provider (internet domain)
and the customer prior to the use of DS


All traffic with the same DS octet is treated the
same by the network service


Routers deal with each packet individually and
do not have to save state information on
packet flows

Internetwork Operation
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DS Octet


Packets are labeled for service handling
by means of the
DS octet


Placed in the
Type of Service

field of an
IPv4 header, or the
Traffic Class

field of
the IPv6 header


RFC 2474: The
leftmost 6 bits

form a
DS
codepoint


The DS codepoint is the DS label used to
classify packets for differentiated services

Internetwork Operation
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DS Codepoint (6 bits)


xxxxx0


Reserved for assignment as standards


000000
: default packet class, i.e. best
-
effort


xxx000: reserved to provide backward
compatibility with the IPv4 precedence service


xxxx11


Reserved for experimental or local use


xxxx01


Reserved for experimental or local use, but
may be allocated for future standards action as
needed

Internetwork Operation
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DS Domain


Within a domain, the interpretation of DS codepoints
is uniform, consistent service is provided

Internetwork Operation
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Routers in DS Domain


Interior nodes (per
-
hop behavior:
PHB
)


Queuing discipline to give preferential
treatment depending on codepoint value


Packet
-
dropping rules to dictate which packets
should be dropped first in the event of buffer
saturation


Boundary nodes


PHB mechanisms


Traffic conditioning

mechanisms

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DS Traffic Conditioner

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DS Traffic Conditioner (cont)


Classifier


Separates submitted packets into different
classes


Based on the DS codepoint or on multiple
fields within the packet header


Meter


Measures submitted traffic for conformance to
a profile


Determines whether a given packet stream
class is within or exceeds the service level
guaranteed for that class

Internetwork Operation
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DS Traffic Conditioner (cont)


Marker


Polices traffic by re
-
marking packets with a
different codepoint as needed


Shaper


Polices traffic by delaying packets as
necessary so that the packet stream in a given
class does not exceed the traffic rate specified
in the profile for that class


Dropper


Drops packets when the rate of packets of a
given class exceeds that specified in the
profile for that class