an ip tutorial tcp/ip naming, addressing, and routing

An IP Tutorial

TCP/IP Naming, Addressing, and Routing

Tutorial Overview

Part 1: Internet Background Part 2: Internet Basics Part 3: How does data get from A to

B? Part 4: IP Routing Part 5: IP QoS Part 6: Internet History, Governance,

References

What is the Internet?

A very large

“network of networks.”

Uses TCP/IP protocols and

packet switching.

Runs on any communications

substrate.

Internet Architecture: WAN

Regional Enterprise

National Service Providers (NSPs)

Interconnection Points (NAPs/MAEs)

Enterprise

Regional

Internet Architecture: Enterprise Attachment

H

H1

H

EthernetNet # 2

FDD Net # 1

R2Private

Line

H4EthernetNet # 3

InternetServiceProvider

H3H2

R1

H7H6H5

Internet - Recent Statistics

20M hosts, 18K adds/day 755K “www”-prefixed hosts, 256%

annual growth rate Highest growth rate: USA (1), Japan (2) 1300K Domains (60/40 USA vs. Rest) Largest domain , “.com” with 4.5M hosts 214 connected IP countries 55 million users

20M hosts, 18K adds/day 755K “www”-prefixed hosts, 256%

annual growth rate Highest growth rate: USA (1), Japan (2) 1300K Domains (60/40 USA vs. Rest) Largest domain , “.com” with 4.5M hosts 214 connected IP countries 55 million users

Internet Growth 1969-1997Internet Growth 1969-1997

1

10

100

1000

10000

100000

1000000

10000000

100000000

1969

Jun-

74

Aug-8

1

Aug-8

3

Oct-8

5

Nov-8

6

Jul-8

8

Jan-

89

Oct-8

9

Jan-

91

Oct-9

1

Apr-9

2

Oct-9

2

Apr-9

3

Oct-9

3

Jul-9

4

Jan-

95

Jan-

96

Jan-

97

Hosts

Networks

Domains

Worldwide Networks Growth

0

20

40

60

80

100

120

140

160

180

Sep-91

Dec-91

Mar-92

Jun-92

Sep-92

Dec-92

Mar-93

Jun-93

Sep-93

Dec-93

Mar-94

Jun-94

Sep-94

Dec-94

Mar-95

Jun-95

Sep-95

Dec-95

Mar-96

Jun-96

Sep-96

Dec-96

Mar-97

Jun-97

# o

f co

un

trie

s

Internet Bitnet UUCP FidoNet OSI

Internet Traffic Statistics

Internet NAP traffic ~ 1 Gbps, growing at 5x/year

Total Internet Bandwidth ~ 350 Gbps World’s telecom traffic ~ 1 Tbps

Internet NAP traffic ~ 1 Gbps, growing at 5x/year

Total Internet Bandwidth ~ 350 Gbps World’s telecom traffic ~ 1 Tbps

Comparing Internet Growth

Telephone Lines: CAGR* = 5.1% Cellular Phones: CAGR = 68.9% Internet Users: CAGR = 113.1%

* Compounded Annual Growth Rate

Telephone Lines: CAGR* = 5.1% Cellular Phones: CAGR = 68.9% Internet Users: CAGR = 113.1%

* Compounded Annual Growth Rate

Moore’s Law vs. Internet Growth

Moore’s Law PC Performance GrowthPC Performance Growth = 2 x Every 18 months= 2 x Every 18 months

Internet GrowthInternet Bandwidth Internet Bandwidth Demand GrowthDemand Growth = 2 x Every 3-4 months= 2 x Every 3-4 months

Tutorial Overview



References

Part 2: Internet Basics

Philosophy and Terminology Addressing Naming and the Domain Name

System

Design Philosophies

Shared Fate Principle connection state maintained at end-

points little state maintained in routers

Addresses are Globally Significant allows local decisions on routing

Provide a Virtual Network Layer separates physical/link layers from

internetwork layer

Connectionless Paradigm

There is no “connection” in IP Packets can be delivered out-of-order Each packet can take a different path to the

destination No error detection or correction in payload No congestion control (beyond “drop”)

TCP mitigates these for connection-oriented applications error correction is by retransmission

Connectionless Example

H

Router

H H

H

H

H

Ethernet

FDDI

Router

PrivateLine

HH H

Ethernet

InternetServiceProvider

Internet Protocol Architecture

RTPRTP

LANsLANs PPPPPPATMATM FRFR

TCPTCP UDPUDP OSPFOSPF

BGPBGP

SNMPSNMPDNSDNSTELNETTELNETFTPFTP

SMTPSMTP

HTTPHTTPPingPing

ICMP

IP

RIPRIP

10/100BaseT10/100BaseT Dedicated B/W: DSx, SONET, ...

Dedicated B/W: DSx, SONET, ...

Circuit-Switched B/W: POTS, SDS, ISDN, ...

Circuit-Switched B/W: POTS, SDS, ISDN, ...

CDPDCDPD

WirelessWireless

OSI Hierarchy

Physical SONET, T1, T3

Link Ethernet, FDDI Circuit, ATM, FR

switches Network

Routing, Call control IP internetworking

Physical

Transport

Network

Link

Application

Presentation

Session

1

4

3

2

7

6

5

OSI Hierarchy

Transport Error and congestion

control TCP, UDP

Session, Presentation, Application Data, voice encodings Authentication web/http, ftp, telnetPhysical

Transport

Network

Link

Application

Presentation

Session

1

4

3

2

7

6

5

TCP/IP: Postal Analogy

IP Packets are like Postcards Globally significant To/From Addresses Finite but variable length content Variable delays Delivery failures Out-of-order deliveries May take different routes

In networking language, IP is “connectionless”

TCP: Postal Analogy

TCP is like sending a Novel on Postcards Network delivers postcards “best effort” Endpoints handle all service actions above “best

effort”– Page numbering (ordering, duplicate

detection)– Positive Acknowledgment– Retransmission on Timeout

In networking language, TCP is “connection-oriented”

IP Network Model

The Internet is a “network of networks”

A network is a collection of hosts that can communicate directly among each other Any pair can communicate The network defines how the pair

exchanges information

IP Network Model

An internet is a concatenation of networks The networks involved may be (and

usually are) heterogeneous An end-to-end path is achieved by

concatenating the transport of data over possibly multiple networks

A Router mediates the differences between the preceding and succeeding networks in the concatenation

Ramifications of Design Principles

Hosts contain connection state Amount of state maintained is

determined by the application Not all applications require the same

amount of state (e.g., reliable delivery) Network elements contain no

connection state or “soft” state “Soft” state is state that can be lost

and refreshed without completely losing the “connection”


Since intermediate systems do not maintain “hard” state, requested QoS is difficult to manage When soft state is lost, intermediate

systems will not be able to maintain the QoS (the information on what the QoS was is lost momentarily)


IP routers take actions independent of other routers to forward data toward its destination IP routers make local decisions only; there

is no network-wide coordination a bad routing decision by one router can be

corrected by its neighbors a failure of a router does not affect the

forwarding of traffic to a destination not directly attached to the failed router


Implementation Performance Varies Most implementations are highly

optimized for the most common case Use of other IP features can cause

significant performance degradation– out-of-order datagram deliver– use of IP options

C3

C1

C2

Path for C1 <> C3

Path for C2 <> C3

"Longer" paths become under-

utilised

"Longer" paths become under-

utilised

Bandwidth Bottlenecks

Routing Protocols Create A Single "Shortest Path"

C3

C1

C2

PVC C1 <> C3PVC C2 <> C3

Engineering-Out The Bottlenecks

ATM Switches Enable Traffic Engineering

C3

C1

C2

LSP C1 <> C3

LSP C2 <> C3

MPLS Takes Over

MPLS LSRs Enable Traffic Engineering

DS

Low delay (preferred for VoIP traffic)

High bandwidth (preferred for FTP)

MPLS Path Creation:Quality of Service Refinements

Source device (S) determines the type of path on the basis of the data

Hosts, Subnets, & Routers

IP Subnet(No IP Processing) RR

IP PacketsIP Packets

Protocols above IPProtocols above IP

HostHostHostHost

RR

RR

RR

IP Subnet(No IP Processing)


IP ProcessingIP Processing


IP Subnet: Ethernet, Private Line, Frame Relay, ATM, ….IP Subnet: Ethernet, Private Line, Frame Relay, ATM, ….

Names and Addresses

Every TCP/IP device (optionally) has a “name”. Each IP subnet interface on the device has an IP “address” and one or more “subnet specific addresses” (sometimes called “physical addresses”).

Names and Addresses

Name: Character string based on a “domain” structure, e.g., www.att.com

IP Address: A.B.C.D (4-octet binary string consisting of “subnet id” and “host id”)

Subnet Specific Addresses

Subnet Specific Addresses are often referred to as “physical addresses” but are really either true network addresses (like E.164,

ATM End System Addresses) link layer addresses (like Frame Relay

DLCIs or ATM VPI/VCI)

Examples of Subnet Specific Addresses

Ethernet, IEEE 802.3 MAC/link Frame Relay (E.164/network,

DLCI/link) Circuit-switched (E.164/network) ATM (E.164/network, AESA/network,

VPI/VCI/link) Dedicated Serial Line (null subnet

specific address)

Subnet Confusion Possible

Note: the term “subnet” is also used as a logical subdivision of the IP address space which is meant should be clear from

the context

Names & Addresses: An Example

H

R

R

H

Circuit-switched Net(IP subnet id = A)

ATM Network(IP subnet id = B)

R

R

Ethernet(IP subnet id = D)

Name: www.att.comName: www.att.com

IP: A.1IP: A.1E.164: 908-949-1254E.164: 908-949-1254

Private Line Net(IP subnet id = C)

IP: A.2IP: A.2E.164: 212-546-1355 E.164: 212-546-1355

IP: A.3IP: A.3E.164: 201-876-4477E.164: 201-876-4477

IP: C.1IP: C.1

IP: C.2IP: C.2

IP: B.1IP: B.1NSAP: af26c9NSAP: af26c9

IP: B.2IP: B.2NSAP: cd675fNSAP: cd675f

IP: B.3IP: B.3NSAP: ed43fcNSAP: ed43fc

VPI/VCI: 222VPI/VCI: 222



VPI/VCI: 555VPI/VCI: 555VPI/VCI: 898VPI/VCI: 898


IP: D.1IP: D.1MAC: efd462MAC: efd462

IP: D.2IP: D.2MAC: 458ef9MAC: 458ef9

IP: D.3IP: D.3MAC: b23cd1MAC: b23cd1

IP Addresses

IP version 4 addresses are all 24 bits in length

Representation is in “dotted-decimal” notation: A.B.C.D A is the decimal number equivalent to the 8-

bit quantity in the first octet B is the decimal number equivalent to the 8-

bit quantity in the second octet, etc. All IP addresses contain a “network” part

and a “host” part

IP Address Network/Host Parts

When specific boundary between network and host parts is needed: a “subnet” mask is paired with the address

– the mask is ANDed with the address to obtain the network part

– e.g., 255.255.255.0 means that the first 3 octets are network and the last octet is host, or

a specific bit-length is included– the length is placed after a slash separating the

address from the length

Example: Subnet/Host Address

Example: Host snipe.ho.att.com IP address is 135.16.157.112 IP network is 135.16.157.0

255.255.255.0 IP network is 135.16.157.0/24

Which representations to use is determined by local software

Classless Inter-Domain Routing (CIDR)

IP addresses originally had a “natural” network length Class A addresses had an 8-bit

network and 24-bit host part Class B addresses had a 16-bit

network and 16-bit host part Class C addresses had a 24-bit

network and 8-bit host part

CIDR and Addresses

Later subnet extensions were allowed the natural network part could be

extended out to, but not including, the host part

when this is done, a subnet mask is required to allow various IP processing stages to determine the network/host boundary

CIDR and Addresses

CIDR removes the “natural” network length subnets can now be any prefix of

length 1 to 31 bits this required changes to routing

protocols to allow carriage of the subnet length field

IP Packet Structure

SS DD ...... DataData

S = Source Address (“Calling Number”)S = Source Address (“Calling Number”)

D = Destination Address (“Called Number”)D = Destination Address (“Called Number”)

HeaderHeader

IP Packet Structure

4-bitVersion

4-bitHeaderLength

8-bitType of Service

(TOS)16-bit Total Length (Bytes)

16-bit Identification3-bitFlags 13-bit Fragment Offset

8-bit Time to Live(TTL) 8-bit Protocol 16-bit Header Checksum

32-bit Source IP Address

32-bit Destination IP Address

Options (if any)

Payload

20-byte20-byteHeaderHeader

Tutorial Overview



References

Part 3: How Does a Datagram get from A to B?

Host Configurations How does a host get an IP address? Other fixed configurations: DNS server

and default router Name to address translation Mask and Match on Address

Decision: resolve the address or forward? Address resolution

Getting from A to B

Host address resolution protocol (ARP) and table

Host forwarding table

Host Configurations

A host needs to be configured to know 3 IP addresses Its own IP address The IP address of its DNS server (two

are preferred, primary and secondary) The IP address of the default router it

will use to reach hosts not on its local (sub)network

These can be either static (manual) or dynamic configurations

Host Configurations

A host also needs to know the subnet mask (or prefix length) of its own IP address subnet mask uses a 24-bit quantity

with logical AND to extract the IP subnet

prefix length explicitly indicates what part of the local IP address is the IP subnet

Dynamic Configuration

Dynamic Host Configuration Protocol (DHCP) Uses central administration to maintain

a server The protocol uses the host’s Ethernet

address (on I/F) to identify it The DHCP server responds with the

specific configuration information for that host

DHCP at Bootup

DHCPServer

Name: myhost.att.comName: myhost.att.comIP addr: 135.16.12.44IP addr: 135.16.12.44MAC addr: ef655cMAC addr: ef655c

Ethernet

No IP AddrNo IP Addr

DHCP: Dynamic Host Configuration ProtocolDHCP: Dynamic Host Configuration Protocol

Broadcast DHCP Request: Broadcast DHCP Request:

Source. MAC addr. = Source. MAC addr. = ef655cef655c

DHCP Response

Name/Address TranslationsIP Over Ethernet

DNS

Name: www.att.comIP addr: 135.16.12.44MAC addr: ef655c

Ethernet

http://www.att.com

www.att.com?

135.16.12.44

Dest. IP Addr.= 135.16.12.44

DNS: Domain Name ServerDNS: Domain Name ServerARP: Address Resolution ProtocolARP: Address Resolution Protocol

ARP: 135.16.12.44? ef655c

Dest. MAC addr. = ef655c

Name/Address TranslationsIP Over ATM Network

DNS

Name: www.att.comName: www.att.comIP addr: 135.16.12.44IP addr: 135.16.12.44NSAP addr: ef655cNSAP addr: ef655c

ATM Network

http://www.att.comhttp://www.att.com

www.att.com?

135.16.12.44

Dest. IP Addr.=Dest. IP Addr.= 135.16.12.44135.16.12.44

DNS: Domain Name ServerDNS: Domain Name ServerARPS: Address Resolution ProtocolARPS: Address Resolution Protocol ServerServer

ARPS

135.16.12.44?

ef655c

SVC set-up to “ef655c”Assign VPI/VCI = 1234

VPI/VCI = 1234VPI/VCI = 1234

Name to Address Translation

The host obtains a name from the user www.att.com

The “resolver” is called to map the name to an address

A name resolution query is sent to the configured DNS server

Name to Address Translation

The DNS server responds with the address(es) corresponding to the

name, if it knows it, or the address of another server that should

know more Translation can be name to:

Host address Mail exchange other information (e.g., services supported)

Name to Address: Example

A host named coyote.acme.com wants to know the address of roadrunner.aspca.org Assume the configured name server

for coyote is dns.acme.com


dns.acme.com receives a name query for roadrunner.aspca.org this DNS server has no idea about

– roadrunner.aspca.org, or– aspca.org

but it knows org is handled by dns.internic.net and its IP address

dns.acme.com returns a reply referring to the address of dns.internic.net


coyote.acme.com sends a query to dns.internic.net for roadrunner.aspca.org

dns.internic.net looks in its database and finds it doesn’t know about roadrunner.aspca.org but it does know that the name server for

aspca.org is called dns.aspca.org at a.b.c.d


dns.internic.net replies with a referral to dns.aspca.org at a.b.c.d

coyote.acme.com sends a query to dns.aspca.org for roadrunner.aspca.org dns.aspca.org finds the entry and replies

with the address The server will also respond with any

other information it has for that name

Hierarchical Structure of the DNS

rootroot

arpaarpa comcom eduedu govgov intint milmil netnet orgorg usus ukuk inin ……..

attatt

wwwwww

attatt vava

worldnetworldnet restonreston

cnricnri

top leveltop leveldomainsdomains

second levelsecond leveldomainsdomains

Administration of the Domain Name System

Top Level Domains are assigned and a set of top level servers are maintained Internet Society is owner

(http://www.isoc.org) Internet Assigned Number Authority

within ISOC contracts actual running of top-level servers (3 sites: US, Europe, Asia/Pacific)

Administration of the Domain Name System

Within a top level domain names are created and assigned administration is delegated to that

subordinate name for each subordinate name, a minimum of two

servers must answer for that name: a primary and at least one secondary

the primary is the point of administration secondaries are updated automatically using

a domain/zone transfer protocol

Forwarding: Local or Remote?

Once the DNS returns the destination IP address, the host must determine whether it is local or remote local: the subnet the sender is connected to

– there is a presumption that all local hosts are directly reachable

– for example all hosts on the same Ethernet are directly reachable

remote: not local and therefore must be reached via a router– the router must be local

Forwarding: Local or Remote?

The determination of local or remote is based on comparing the IP subnet of the source with that of the destination If the local IP subnets match, the two hosts

are local to each other The assignment of IP addresses must

maintain this rule! This is often called “mask and match”

Local: Send it Directly

If the destination is local, then it can be sent directly but you first need to know the

destination host Ethernet address (this generalizes for any layer 2

subnet)

Local: Send it Directly

Given the IP address of a local destination, use the Address Resolution Protocol (ARP) ARP is not based on IP, but rather

supports IP ARP relies on broadcast of a request

and a replyARP Request:My Ethernet address: ef655cMy IP address: 135.16.157.23Your Ethernet address: ?Your IP address: 135.16.157.15

ARP Reply:Your Ethernet address: ef655cYour IP address: 135.16.157.23My Ethernet address: fc893eMy IP address: 135.16.157.15

ARP Cache

ARP replies are seen by all local hosts Each host maintains an ARP cache

mapping between IP address and Ethernet (layer 2) address

each cache entry times out (approx. 10 minutes)

the cache is consulted for address resolution before an ARP request is sent

Remote: Send it to the Router

If the destination is remote (subnet match fails) then send it to the local router the router has a local IP address use ARP or the ARP cache to translate to a

layer 2 address Once the Router has the datagram

uses its FIB to determine the next hop the entire process repeats at this point

Sending Over Point-to-Point Links

Previous discussions assumed a broadcast network for transmission

IP treats a point-to-point link as a subnet with exactly two hosts sending to the “other” end is both

broadcast and unicast point-to-point examples: private line,

frame relay PVC, ATM PVC

Data Transfer

Once the subnet and interface is selected, data transmission uses the underlying layer 2 medium

IP is encapsulated in a multiprotocol sublayer (may be different by medium)

The multiprotocol PDU is encapsulated using the appropriate layer 2 mechanism for that medium

Transmission begins

Data Transfer Over Frame-based Networks

File

TCP

IP

Frame(Ethernet, FR, PPP)

Data Transfer Over Cell-based Networks

File

TCP

IP

Adaptation

ATM Cells

Tutorial Overview



References

Part 4: IP Routing

Elements of IP Routing Internet Routing Architecture and

Autonomous Systems Interior Routing Protocols (RIP,

OSPF, IS-IS) Exterior Routing Protocols (BGP)

Elements of IP Routing

IP routing is done at each IP capable node at all routers at all hosts (even though it may be

much simplified)

IP Routing & Forwarding

IP Routing is a dynamic, fully distributed process. Does not rely on any centralized administration.

Packet Forwarding is a hop-by-hop process. Each entity (host or router) only forwards the packet to another entity (host or router) attached to its local IP subnet.

H

R

R

H

IP SubnetIP Subnet

IP SubnetIP Subnet

IP SubnetIP Subnet

IP SubnetIP SubnetR

RSourceSource

DestinationDestination

Internet Routing Architecture

AutonomousSystem (AS)





Autonomous System: A collection of IP subnets and routersAutonomous System: A collection of IP subnets and routers under the same administrative authority.under the same administrative authority.

Interior Routing ProtocolInterior Routing Protocol

Exterior Routing ProtocolExterior Routing Protocol

Internet Routing Hierarchy

The Internet is composed of Autonomous Systems

Each Autonomous System is an administrative entity that Uses Interior Gateway Protocols (IGPs) to

determine routing within the Autonomous System

Uses Exterior Gateway Protocols (EGPs) to interact with other Autonomous Systems

ISPs and Autonomous Systems

A Service Provider may have multiple Autonomous Systems within its operating network The AT&T WorldNet dial platform and

Common Backbone were two separate ASs that have merged

There are two ASs within the WorldNet Common Backbone: one for Internet Gateway Routers (IGRs) and one for the rest

Routing’s 3 Aspects

Acquisition of information about the IP subnets that are reachable through an internet static routing configuration information dynamic routing information protocols

(e.g., BGP4, OSPF, RIP, ISIS) each mechanism/protocol constructs a

Routing Information Base (RIB)

Routing Aspect #2

Construction of a Forwarding Table synthesis of a single table from all the

Routing Information Bases (RIBs) information about a destination subnet

may be acquired multiple ways a precedence is defined among the RIBs

to arbitrate conflicts on the same subnet Also called a Forwarding Information

Base (FIB)

Routing #3

Use of a Forwarding Table to forward individual packets selection of the next-hop router and

interface hop-by-hop, each router makes an

independent decision

RIB Construction

Multiple routing protocols may run on the same router static routing Interior Gateway Protocols, e.g., OSPF Exterior Gateway Protocols, e.g., BGP

RIB Construction

Each routing protocol builds its own Routing Information Base (RIB)

Each protocol has its own “view” of “costs” e.g., OSPF is administrative weights e.g., BGP4 is Autonomous System

path length

FIB Construction

An algorithm is used to choose one next-hop toward each IP destination known by any routing protocol the set of IP destinations present in any

RIB are collected if a particular IP destination is present

in only one RIB, that RIB determines the next hop forwarding path for that destination

FIB Construction

Choosing FIB entries, cont.. if a particular IP destination is present in

multiple RIBs, then a precedence is defined to select which RIB entry determines the next hop forwarding path for that destination

This process normally chooses exactly one next-hop toward a given destination

There are no standards for this; it is an implementation (vendor) decision

FIB Contents

IP subnet and mask (or length) of destinations can be the “default” IP subnet

IP address of the “next hop” toward that IP subnet

Interface id of the subnet associated with the next hop

Optional: cost metric associated with this entry in the forwarding table

Packet Forwarding

Forwarding is the process of determining where a particular datagram should be sent next involves searching the FIB for the next

hop IP address and interface Uses the “longest matching prefix”

several prefixes may have common upper parts, the longest one matching is used

Longest Matching Prefix

Next hop for “101010111...” is 135.17.21.1

Prefix Length N ext H op

1010110 7 135.17.21.4

10101 5 135.17.21.1

101 3 135.17.21.4

Routing Information Base Construction

A dynamic, fully distributed process done for each routing protocol being run

Distance Vector and Link State routing are the two basic techniques.

Distance Vector and Link State

Distance Vector Accumulates a metric hop-by-hop as

the protocol messages traverse the subnets

Link State Builds a network topology database Computes best path routes from

current node to all destinations based on the topology

Distance Vector Protocols

Each router only advertises to its neighbors, its “distance” to various IP subnets

Each router computes its next-hop routing table based on least cost determined from information received from its neighbors and the cost to those neighbors

Distance Vector

Attempts to minimize messaging overhead and memory requirements at the expense of slower convergence

Needs careful design to avoid problems packet looping, or counting to infinity split horizon with poisoned reverse

– if A routes to X via B , then B should not try to route to X via A (loop formation)

– A sends to B updates that list X with infinite (poisoned) cost

Distance Vector RIB Construction

H

R

R

HR

R

IP Subnet “D”Cost = 2

A.1A.1

A.2A.2

A.3A.3

C.1C.1

C.2C.2B.1B.1

B.2B.2

B.3B.3

D.1D.1

D.2D.2

D.3D.3

Cost to D = 2Next Hop = direct


Cost to D = 5Next Hop = A.2

Cost to D = 4Next Hop = C.2

Cost to D = 3Next Hop = B.2

IP Subnet “B”Cost = 1

IP Subnet “C”Cost = 2

IP Subnet “A”Cost = 2


Packet Forwarding

H

R

R

H

IP Subnet “A”Cost = 2


R

R


A.1A.1


A.2A.2

A.3A.3

C.1C.1

C.2C.2B.1B.1

B.2B.2

B.3B.3

D.1D.1

D.2D.2

D.3D.3



Cost to D = 5Next Hop = A.2

Cost to D = 4Next Hop = C.2

Cost to D = 3Next Hop = B.2

D.1D.1

D.1

D.1

D.1

D.1

D.1D.1 D.1D.1


Distance Vector RIB Parameters

Accumulated cost cost is a constant administrative

assignment for each subnet assignment is typically “1” for each

subnet (equivalent to hop-count) included in routing protocol exchange

Time the update was received (for timeout)

Distance Vector RIB Parameters

The next-hop the entry was received from sender’s id is included in routing protocol

exchange Accumulated Hop count and

Maximum Hop Count used to detect cycles hop count included in routing protocol

exchange

Distance Vector: Additions

When a router learns of new reachable subnets at router startup when an interface in enabled or

restored to service A routing update is broadcast to all

neighbors

Distance Vector: Additions

Any router receiving the packet compares the cost it received in the new packet with that in its RIB

If the cost is smaller or the subnet is new the new entry is used in the RIB the new entry is broadcast to all its

neighbors (except the one from which it was received)

Distance Vector: Removals

Each RIB entry is aged a timeout defines when an entry is

removed from the RIB Periodically, each router re-

advertises all the routes it knows to its neighbors this can be done in many ways: from

simple neighbor hellos to enumeration of all routes

Distance Vector: Removals

If a neighbor does not respond within a timeout, all routes learned from that neighbor are removed

Route removal may be advertised to neighbors

Link State Protocols

Each router broadcasts to all the routers in the network the state of its locally attached links and IP subnets

Each router constructs a complete topology view of the entire network based on these link state updates and computes its next-hop routing table based on this topology view


Attempts to minimize convergence times and eliminate non-transient packet looping at the expense of higher messaging overhead, memory, and processing requirements

Allows multiple metrics/costs to be used


The “broadcast” of link state from one router to all others uses a variety of mechanisms true broadcast when the layer 2

subnet interconnecting the routers supports broadcast

multicast among the routers when the layer 2 subnet supports that (e.g. Frame-Relay, ATM)

hop-by-hop flooding as a last resort


Transmission of link state must be done reliably the protocol assumes that the topology

databases of all nodes are identical to prevent routing-loops from forming

acknowledgments from all neighbors are needed

routers must deal with out-of-order delivery of updates, replicates, etc., all of which requires processing time

Link State RIB Parameters

Topology Database Router IDs Link IDs

– From Router ID– To Router ID

Metric(s) Sequence number

List of Shortest Paths to Destinations

Link State Operation: Additions

Flooding Algorithm each router announces itself and each link

it is attached to announcements by broadcast or multicast

or unicast to all neighbors Designated router used on broadcast nets

– to minimize number of adjacencies

Each router constructs its Topology DB

Link State Operation: Removals

Removals are announcements with the metric set to “infinity”

Adjacencies must be refreshed neighbors use “hello” protocol if a router loses a neighbor, then routes

via that neighbor are recomputed send announcements with link metric to

lost neighbor set to infinity

Link State: Shortest Path

Dijkstra’s Shortest Path First graph algorithm Use yourself as starting point Search outward on the graph and add

router IDs as you expand the front Addresses are associated with routers

Hence the SPF algorithm needs to deal only in the number of routers, not the number of routes

Link State: Shortest Path

R1

R3

R4

R2


A.2A.2

A.3A.3

C.1C.1

C.2C.2B.1B.1

B.2B.2

B.3B.3

D.2D.2

D.3D.3



IP Subnet “A”Cost =3

NextRouter Hop Link

R2 A.3 AR3 B.3 BR4 B.2 B

From R1

From R4R1 B.1 BR2 B.3 BR3 B.3 B

IGP: Routing Information Protocol (RIP)

The first interior routing protocol based on “distance vector” concepts (RFC 1058, 6/1/88, updated to RIP v2 in RFC 1723, 11/15/94)

Limited scalability (max diameter 16) Suffers from problems such as

creation of routing loops creation of “black holes”

IGP: Open Shortest Path First (OSPF)

Current generation interior routing protocol based on “link state” concepts (RFC 1131, 10/1/89, obsoleted by OSPF v2, RFC 1723, 11/15/94)

Supports hierarchies for scalability Fast convergence and loop avoidance Used within the WorldNet Common

Backbone and Dial Platform

IGP: Intermediate System-to-Intermediate System (IS-IS)

OSI routing protocol extended to allow IP (RFC 1142, 12/30/91)

Very similar to OSPF Differences are small and deal mostly with

failure modes Used in many Internet Service Provider

networks Cisco’s implementation of ISIS is believed

to be better than Cisco’s OSPF

IGP: Interior Gateway Routing Protocol (IGRP)

Cisco’s proprietary routing protocol Based on “distance vector”

concepts, but avoids RIP problems Dominant in enterprise networks Cisco’s EIGRP is a hybrid protocol

using both distance vector and link state concepts

EGP: Exterior Gateway Protocol (EGP)

The first exterior routing protocol based on “distance vector” concepts (RFC 0904, 4/1/84)

Designed for a simple tree-structured topology with “regional” networks with a single “backbone.”

Topology restrictions quickly made this protocol obsolete

No longer used widely in the Internet

EGP: Border Gateway Protocol version 4 (BGP4)

The current generation exterior routing protocol based on “path vector” concepts (RFC 1771, 3/21/95)

Supports complex mesh topologies with loop-avoidance

Required protocol for use at Internet exchange points

EGP: Border Gateway Protocol version 4 (BGP4)

Supports policy-based routing by keeping the path of ASs toward the destination e.g., allows filtering out routes

through specified ASs

Tutorial Overview



References

Part 5: IP QoS

Philosophy How things work on the Internet

data voice, video

How IP QoS tries to make them work better

The role of ATM

Internet QoS Philosophy

Things should work with best-effort service best-effort service supports no

explicit bounds on delay, throughput, or packet loss

Selectively do resource reservation if you need things to work better

Maintain only soft state or no state

Protocol Architecture

IP

TCP

HTTPHTTP FTPFTP

UDPUDP

RPCRPC RTP

•reliable transport•resequencing•flow control

•timing recovery•resequencing•adaptive encoding

•delivery not reliable- congestion may cause packet loss

•sequence may not be preserved- packets may follow different paths

•delays variable

DataVoice,Video

Voice, Video, Jitter, & Delay

Packets experience variable delay (jitter) under best-effort service

Receiver can accommodate jitter by adapting the playout point larger jitter implies larger end-to-end delay

Competingtraffic

Ro

ute

r

PlayoutPoint

to Codec

Ro

ute

r

Sliding Windows

Receiver acknowledges successfully received packets

Sender limits number of packets that have been sent but not acknowledged Limit = Window

Window size limits transmission rate

Packets: 1 2 3 4 5 6 7 8 9 10

ACKedby

receiver

sent,but notACKed

cansendnow

can’tsendyet

Data Transport & Packet Loss

TCP probes for bandwidth by increasing its window size until loss occurs, then backs off and tries again loss more critical than delay for data

ReceiverTransmitter

User DataAcknowledgment

W=1

W=2

W=3

W=4

WindowSize

Data Transport & Packet Loss

TCP decreases window size if hole detected in window or if time-out occurs loss of more than one packet per

round-trip time typically results in an over-reaction to congestion

AckUser Data

D Duplicate Ack

ReceiverTransmitterW=4

D D

W=2 R

RetransmissionR

Internet Work on Resource Management and QoS Support

SchedulingQoS

RoutingSignaling

LittleEffortHere

MostEffortHere

Routing: Best-Effort vs. QoS

Best-Effort Routing Routing based on

hop counts facility speeds

QoS requirements not met if resources are insufficient on best-effort path

QoS Routing Routing based on

hop counts facility speeds bandwidth and delay

requirements bandwidth

availability QoS requirements

supported if feasible path through network exists

Flow Sequence of packets defined by

common destination address or subnet and possibly also by one or more of the following attributes:

Source IP Address/Subnet Protocol (TCP or UDP) Source TCP/UDP port number Destination TCP/UDP port number Type of Service (TOS) field

Integrated Services Flow-Based QoS

signaled via the ReSource reserVation Protocol (RSVP)

per-flow reservations requested by receiver, propagated router-by-router

difficult to implement; not widely deployed

Class-Based QoS (Differential Services) flows mapped into small # of classes packets marked (via TOS field) at network

edge and prioritized in network interior based on marking

ServicesQoSGoal

RS VP DiffererentialS ervices

ReduceDelays

GuaranteedQoS

Priority

ImproveThroughput

ControlledLoad

Assured

With exception of Guaranteed QoS service, QoS objectives are described qualitatively, not quantitatively

With Freedom Comes Responsibility: Token Buckets

ArrivingPacket

TokenAvailable?

Tag packet,drop packet,

or treat as best effort

No

Token

Token bucket defines token rate & bucket depth Use of token buckets common to all Integrated

Services Similar to ATM and Frame Relay networks

RSVP1.Forward data flow

established2. PATH message traces

route from sender to receiver

3. RESV message backtracks route of PATH message and installs reservation Soft state periodically

refreshed by new PATH and RESV messages

Interior routers maintain per-flow state

R

R

R

3.

1.

2.

Sender

Receiver

Differential ServicesBandwidth Brokers

Signaling is between agents from adjacent Autonomous Systems Agents generically called “Bandwidth Brokers (BBs)”

Interior routers not necessarily aware of individual bandwidth allocations pre-provisioned rates per class between

administratively separate networks

UserNet 1

V

BB10 Mbpsto D

ISP

50 BB

User Net 2

20 BB

D

OK OK OK

Algorithms for Frame Scheduling and Buffer Management

Weighted Fair Queueing (WFQ) link bandwidth allocated per-flow or per-

class in proportion to a configured weight supports minimum bandwidth guarantees

and fair allocation of excess bandwidth

Random Early Detection (RED) randomizes packet loss to optimize TCP

performance drop probabilities depend on buffer

occupancy and possibly on packet priority (Weighted RED)

Voice Delay w/ Two WFQ Implementations(Bennett and Zhang)

Accounts for queueing delay at single DS3 link saturated by background traffic

Assumes 9 Mbps of voice With First-In-First-Out queueing (rather than WFQ), voice

delays in the hundreds of msec would result

20 ms

15 ms

10 ms

5 ms

10 ms

20 ms

30 ms

Example: 150 msec budget for one-way voice delay (gateway-gateway) Packetization + Look Ahead (G.729): 45 msec

assumes 4 frames per packet 10 msec per frame and 5 msec look ahead

DSP Processing: 5 msec Propagation: 50 msec Queueing: 25 msec (gateway-to-gateway) Buildout: 25 msec

» To consistently live within budget, voice must be prioritized at links, or links must be dedicated to voice

Link Sharing

Provides characteristics of a private network Implemented via WFQ or other service

discipline that guarantees bandwidth shares experience with layer-2 services (frame relay and

ATM) indicates that sub-classes must be queued separately to systematically divide bandwidth between them

1.0

.01 .12 .08.05 .03 .06Priority Assured Best

-Effort

...

155 Mbps

.21.14 ...

Priority

Assured

Best-Effort

Customer 1 Customer N

Role of ATM

ATM can provide a “designer link layer” for routers Link sharing implemented through ATM Virtual Circuits

(VCs) About 16K VCs supported per OC12 (today) with

queueing and QoS differentiation on a per-VC basis QoS routing at ATM layer can compensate for lack

thereof at IP layer

S1 S2R1 R3

R2 R4

Priority VCAssured VCBest-Effort VC

Tutorial Overview



References

Internet Timeline: 1960s

1965: ARPA sponsors a study on “cooperative network of time-sharing computers”

1969 ARPANET commissioned First Request for Comment (RFC)

published: “Host Software”


Store-and-forward networks Email and conferencing technologies

developed Telnet and FTP developed (1972/73) Metcalfe outlines ideas behind Ethernet BBN starts Telenet, first public packet

data service (1974) UUCP developed at Bell Labs (1976)


TCP/IP suite of protocols (1982) Transmission Control Protocol (TCP) Internet Protocol (IP) Concatenates heterogeneous

networks using IP Internet Activities Board created

(1983) Domain Name System intro. (1984)


NSFNET created (1986) backbone 56 kbps links (1986), T1 (1988) regional networks also created

UUNET founded for commercial netnews service (1987)

First commercial email exchanges via Internet (1989) MCI Mail and CompuServe


ARPANET ceases to exist (1990) First commercial dial service: The World

(1990) Commercial Internet eXchange (CIX)

association (1991) NSFNET backbone to T3 (1991)

1 terabyte/month 10 giga-packets/month

Multicast backbone established (1992)


World Wide Web (1993) Mosaic from NCSA leads to Netscape Navigator

and MS Internet Explorer WWW growth is 341,634% per year

NSFNET reverts to a research net (1995) very high-speed Backbone Network Service

(vBNS) at OC-3, contract to MCI The Internet “completely” commercial

AT&T WorldNet becomes the largest pure Internet Service Provider

Internet Governance

Internet Society Internet Activities Board (IAB) Internet Engineering Steering Group

(IESG) Internet Engineering Task Force

(IETF) Internet Research Task Force (IRTF)

IETF Areas

Application Area Internet Area Operations & Management Area Routing Area Security Area Transport Area User Services Area

Request for Comments

RFC process is based on rough consensus representation is individual, not based on

company or other affiliation Internet Drafts are submitted to IETF

working groups Internet Draft to Proposed Standard

stable specification agreed to by IESG all design choices resolved

Request for Comments

Proposed to Draft Standard Two independent and interoperable

implementations including all options IESG approval Draft Standard is normally considered final

Draft Standard to Internet Standard Exhibits a high degree of technical maturity Provides significant benefit to the community

References

Comer, Internetworking with TCP/IP, Prentice-Hall, 1988.

Huitema, Routing on the Internet, Prentice-Hall PTR, 1995.

Perlman, Interconnections: Bridges and Routers, Addison-Wesley, 1992.

Stevens, TCP/IP Illustrated, volumes 1-3, Addison-Wesley, 1995.

References

Hobbes’ Internet Timeline, IETF RFC 2235, Nov. 1997.

References on the Web

www.isoc.org The Internet Society

www.iab.org Internet Activities Board

www.ietf.org RFCs and Internet drafts meeting schedules

References on the Web

www.internic.net RFCs and Internet drafts IP address and DNS registration

information Databases of various and sundry

Internet related “stuff”

Part 7: Miscellaneous

Load Balancing

A particular routing protocol may determine there are multiple paths toward a destination with the same “cost” Typical when there are multiple parallel

trunks between routers If a RIB has multiple entries for the

same destination, then the FIB could include one, some, or all of them

Load Balancing

If there is more than one is entry in the FIB for a destination, load balancing is possible round-robin distribution of packets onto

paths hashed distribution attempts to keep

packets with the same source and destination addresses on the same trunk to minimize out-of-order delivery

IP Multicast

Design and purpose Distributed communication model Class “D” addresses MBONE

IP Multicast

Designed for efficient support of one-to-many and many-to-many communications, e.g., Conferencing, etc.

Sender sends one copy addressed to a “multicast group” and the network delivers one copy to each multicast group member.

IP Multicast

Based on a fully-distributed communication model that does not require a centralized “bridge”: Participants join/drop multicast sessions via the Internet Group

Management Protocol (IGMP). Multicast routing protocols (DVMRP, MOSPF, PIM, etc.) are used

for packet routing and delivery.

The Internet Multicast Backbone (MBONE) was deployed between 1988-1992 for experimentation and development of multicast protocols

RIP Messages

Request / Response

Command (Req/Resp)1

Version1

reserved2

Address Family (IP=2)2

reserved2

Address4

reserved8

metric4

May be repeated

RIP Protocol

Updates are sent periodically upon request optional: upon change of metric on

destination (e.g., due to link failure) RIB entries time out and must be

refreshed

RIP Protocol

Convergence times are long because The entire RIB is sent, not just entries that

changed Convergence sometimes encounters loops

– count-to-infinity in RIP means count-to-16– each hop may wait the full period to forward

updates

RIP v1 does not implement CIDR support (v2 does)

an ip tutorial tcp/ip naming, addressing, and routing

Documents

hosts n

n internet users

users n

internet background

n naming

addsday n

terminology n

ip routing n