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TCP/IP Naming, Addressing, and Routing

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Title: TCP/IP Naming, Addressing, and Routing


1
TCP/IP Naming, Addressing, and Routing
An IP Tutorial
2
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

3
What is the Internet?
A very large network of networks. Uses TCP/IP
protocols and packet switching. Runs on any
communications substrate.
4
Internet Architecture WAN
Interconnection Points (NAPs/MAEs)
National Service Providers (NSPs)
Enterprise
Regional
Regional
Enterprise
5
Internet Architecture Enterprise Attachment
H1
Internet Service Provider
H
H
FDD Net 1
R1
R2
PrivateLine
Ethernet Net 2
H7
H6
H5
Ethernet Net 3
H4
H3
H2
6
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


7
Internet Growth 1969-1997
8
Worldwide Networks Growth
9
Internet Traffic Statistics
  • Internet NAP traffic 1 Gbps, growing at
    5x/year
  • Total Internet Bandwidth 350 Gbps
  • Worlds telecom traffic 1 Tbps


10
Comparing Internet Growth
  • Telephone Lines CAGR 5.1
  • Cellular Phones CAGR 68.9
  • Internet Users CAGR 113.1
  • Compounded Annual Growth Rate


11
Moores Law vs. Internet Growth
PC Performance Growth 2 x Every 18 months
Moores Law
Internet Bandwidth Demand Growth 2 x Every
3-4 months
Internet Growth
12
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

13
Part 2 Internet Basics
  • Philosophy and Terminology
  • Addressing
  • Naming and the Domain Name System

14
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

15
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

16
Connectionless Example
H
Internet Service Provider
H
H
FDDI
PrivateLine
Router
Ethernet
Router
Ethernet
H
H
H
H
H
H
17
Internet Protocol Architecture
Ping
FTP
TELNET
HTTP
RTP
SNMP
DNS
BGP
SMTP
RIP
TCP
UDP
OSPF
ICMP
IP
LANs
PPP
ATM
FR
CDPD
Dedicated B/W DSx, SONET, ...
Circuit-Switched B/W POTS, SDS, ISDN, ...
10/100BaseT
Wireless
18
OSI Hierarchy
  • Physical
  • SONET, T1, T3
  • Link
  • Ethernet, FDDI
  • Circuit, ATM, FR switches
  • Network
  • Routing, Call control
  • IP internetworking

19
OSI Hierarchy
  • Transport
  • Error and congestion control
  • TCP, UDP
  • Session, Presentation, Application
  • Data, voice encodings
  • Authentication
  • web/http, ftp, telnet

Application
Presentation
Session
Transport
Network
Link
Physical
20
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

21
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-oriente
    d

22
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

23
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

24
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

25
Ramifications of Design Principles
  • 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)

26
Ramifications of Design Principles
  • 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

27
Ramifications of Design Principles
  • 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

28
Bandwidth Bottlenecks
  • Routing Protocols Create A Single "Shortest Path"

C1
C3
C2
"Longer" paths become under-utilised
Path for C1 ltgt C3
Path for C2 ltgt C3
29
Engineering-Out The Bottlenecks
  • ATM Switches Enable Traffic Engineering

C1
C3
C2
PVC C1 ltgt C3
PVC C2 ltgt C3
30
MPLS Takes Over
  • MPLS LSRs Enable Traffic Engineering

C1
C3
C2
LSP C1 ltgt C3
LSP C2 ltgt C3
31
MPLS Path CreationQuality of Service Refinements
  • Source device (S) determines the type of path on
    the basis of the data

S
D
Low delay (preferred for VoIP traffic)
High bandwidth (preferred for FTP)
32
Hosts, Subnets, Routers
Protocols above IP
Host
Host
IP Subnet (No IP Processing)
IP Subnet (No IP Processing)
R
IP Processing
IP Subnet (No IP Processing)
IP Subnet (No IP Processing)
IP Packets
IP Subnet Ethernet, Private Line, Frame Relay,
ATM, .
33
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).

34
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)

35
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)

36
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)

37
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

38
Names Addresses An Example
IP A.3 E.164 201-876-4477
R
Circuit-switched Net (IP subnet id A)
H
IP A.1 E.164 908-949-1254
IP C.1
IP A.2 E.164 212-546-1355
Private Line Net (IP subnet id C)
R
IP B.1 NSAP af26c9
VPI/VCI 555
IP B.3 NSAP ed43fc
VPI/VCI 898
IP C.2
R
ATM Network (IP subnet id B)
VPI/VCI 222
VPI/VCI 666
IP D.2 MAC 458ef9
VPI/VCI 222
Name www.att.com
VPI/VCI 456
IP B.2 NSAP cd675f
Ethernet (IP subnet id D)
R
H
IP D.3 MAC b23cd1
IP D.1 MAC efd462
39
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

40
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

41
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

42
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

43
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

44
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

45
IP Packet Structure
Header
...
S
D
Data
46
IP Packet Structure
4-bit Header Length
8-bit Type of Service (TOS)
4-bit Version
16-bit Total Length (Bytes)
3-bit Flags
16-bit Identification
13-bit Fragment Offset
20-byte Header
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
47
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

48
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

49
Getting from A to B
  • Host address resolution protocol (ARP) and table
  • Host forwarding table

50
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

51
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

52
Dynamic Configuration
  • Dynamic Host Configuration Protocol (DHCP)
  • Uses central administration to maintain a server
  • The protocol uses the hosts Ethernet address (on
    I/F) to identify it
  • The DHCP server responds with the specific
    configuration information for that host

53
DHCP at Bootup
DHCP Dynamic Host Configuration Protocol
DHCP Response
DHCP Server
Broadcast DHCP Request
Ethernet
Name myhost.att.com IP addr 135.16.12.44 MAC
addr ef655c
Source. MAC addr. ef655c
No IP Addr
54
Name/Address TranslationsIP Over Ethernet
DNS Domain Name Server ARP Address Resolution
Protocol
DNS
www.att.com? 135.16.12.44
ARP 135.16.12.44? ef655c
Ethernet
Name www.att.com IP addr 135.16.12.44 MAC addr
ef655c
http//www.att.com
Dest. MAC addr. ef655c
Dest. IP Addr. 135.16.12.44
55
Name/Address TranslationsIP Over ATM Network
DNS Domain Name Server ARPS Address Resolution
Protocol Server
ARPS
DNS
www.att.com? 135.16.12.44
135.16.12.44? ef655c
ATM Network
SVC set-up to ef655c Assign VPI/VCI 1234
Name www.att.com IP addr 135.16.12.44 NSAP
addr ef655c
http//www.att.com
VPI/VCI 1234
Dest. IP Addr. 135.16.12.44
56
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

57
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)

58
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

59
Name to Address Example
  • 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

60
Name to Address Example
  • coyote.acme.com sends a query to dns.internic.net
    for roadrunner.aspca.org
  • dns.internic.net looks in its database and finds
  • it doesnt 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

61
Name to Address Example
  • 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

62
Hierarchical Structure of the DNS
root
top level domains
.
arpa
com
edu
gov
int
mil
net
org
us
uk
in
second level domains
va
att
att
reston
worldnet
www
cnri
63
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)

64
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

65
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

66
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

67
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)

68
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 reply

ARP Request My Ethernet address ef655c My IP
address 135.16.157.23 Your Ethernet address
? Your IP address 135.16.157.15
ARP Reply Your Ethernet address ef655c Your IP
address 135.16.157.23 My Ethernet address
fc893e My IP address 135.16.157.15
69
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

70
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

71
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

72
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

73
Data Transfer Over Frame-based Networks
File
TCP
IP
Frame (Ethernet, FR, PPP)
74
Data Transfer Over Cell-based Networks
File
TCP
IP
Adaptation
ATM Cells
75
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

76
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)

77
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)

78
IP Routing Forwarding
Source
R
H
IP Subnet
IP Subnet
R
R
IP Subnet
Destination
IP Subnet
R
H
  • 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.

79
Internet Routing Architecture
Autonomous System (AS)
Autonomous System (AS)
Autonomous System (AS)
Autonomous System (AS)
Autonomous System (AS)
Autonomous System A collection of IP subnets and
routers
under the same administrative authority.
Interior Routing Protocol
Exterior Routing Protocol
80
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

81
ISPs and Autonomous Systems
  • A Service Provider may have multiple Autonomous
    Systems within its operating network
  • The ATT 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

82
Routings 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)

83
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)

84
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

85
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

86
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

87
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

88
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

89
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

90
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

91
Longest Matching Prefix
  • Next hop for 101010111... is 135.17.21.1

92
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.

93
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

94
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

95
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

96
Distance Vector RIB Construction
Cost to D 5 Next Hop A.2
A.3
R
Cost to D 4 Next Hop C.2
H
IP Subnet A Cost 2
A.1
C.1
A.2
IP Subnet C Cost 2
R
Cost to D 3 Next Hop B.2
B.1
C.2
B.3
R
IP Subnet B Cost 1
Cost to D 2 Next Hop direct
D.2
Destination
B.2
D.1
IP Subnet D Cost 2
R
H
Cost to D 2 Next Hop direct
D.3
97
Packet Forwarding
Cost to D 5 Next Hop A.2
A.3
R
IP Subnet A Cost 2
Cost to D 4 Next Hop C.2
H
A.1
C.1
A.2
D.1
IP Subnet C Cost 2
R
Cost to D 3 Next Hop B.2
D.1
B.1
C.2
B.3
R
IP Subnet B Cost 1
Cost to D 2 Next Hop direct
D.2
Destination
B.2
Cost to D 2 Next Hop direct
D.1
IP Subnet D Cost 2
R
H
D.3
D.1
D.1
D.1
98
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)

99
Distance Vector RIB Parameters
  • The next-hop the entry was received from
  • senders 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

100
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

101
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)

102
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

103
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

104
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

105
Link State Protocols
  • 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

106
Link State Protocols
  • 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

107
Link State Protocols
  • 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

108
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

109
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

110
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

111
Link State Shortest Path
  • Dijkstras 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

112
Link State Shortest Path
From R1
A.3
NextRouter Hop Link R2
A.3 A R3 B.3 B R4 B.2
B
R2
IP Subnet A Cost 3
C.1
A.2
IP Subnet C Cost 2
R1
B.1
C.2
B.3
R3
IP Subnet B Cost 2
From R4 R1 B.1 B R2
B.3 B R3 B.3 B
D.2
B.2
IP Subnet D Cost 3
R4
D.3
113
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

114
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

115
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
  • Ciscos implementation of ISIS is believed to be
    better than Ciscos OSPF

116
IGP Interior Gateway Routing Protocol (IGRP)
  • Ciscos proprietary routing protocol
  • Based on distance vector concepts, but avoids
    RIP problems
  • Dominant in enterprise networks
  • Ciscos EIGRP is a hybrid protocol using both
    distance vector and link state concepts

117
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

118
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

119
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

120
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

121
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

122
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

123
Protocol Architecture
Voice, Video
Data
HTTP
FTP
RPC
RTP
  • timing recovery
  • resequencing
  • adaptive encoding

UDP
TCP
  • reliable transport
  • resequencing
  • flow control
  • delivery not reliable
  • - congestion may cause packet loss
  • sequence may not be preserved
  • - packets may follow different paths
  • delays variable

IP
124
Voice, Video, Jitter, Delay
Router
Router
to Codec
Playout Point
Competing traffic
  • 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

125
Sliding Windows
Packets 1 2 3 4 5 6 7 8
9 10
can send now
cant send yet
ACKed by receiver
sent, but not ACKed
  • Receiver acknowledges successfully received
    packets
  • Sender limits number of packets that have been
    sent but not acknowledged
  • Limit Window
  • Window size limits transmission rate

126
Data Transport Packet Loss
Window Size
W1
Receiver
W2
Transmitter
W3
W4
User Data
Acknowledgment
  • 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

127
Data Transport Packet Loss
W4
Receiver
Transmitter
D
D
W2
R
Ack
Duplicate Ack
D
Retransmission
R
  • 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

128
Internet Work on Resource Management and QoS
Support
Scheduling
QoS Routing
Signaling
Little Effort Here
Most Effort Here
129
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

130
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

131
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

132
Services
  • With exception of Guaranteed QoS service, QoS
    objectives are described qualitatively, not
    quantitatively

133
With Freedom Comes Responsibility Token Buckets
Tag packet, drop packet, or treat as best effort
Arriving Packet
No
Token Available?
Token
  • Token bucket defines token rate bucket depth
  • Use of token buckets common to all Integrated
    Services
  • Similar to ATM and Frame Relay networks

134
RSVP
  • 1.Forward data flow established
  • 2. 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

Sender
2.
R
1.
R
R
3.
Receiver
135
Differential ServicesBandwidth Brokers
User Net 1
BB
BB
BB
10 Mbps to D
D
OK
OK
OK
V
User Net 2
ISP
  • 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

136
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)

137
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

138
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

139
Link Sharing
155 Mbps
1.0
...
.21
.14
Customer 1
Customer N
...
.03
.12
.06
.01
.08
.05
Priority
Assured
Best- Effort
Priority
Assured
Best- Effort
  • 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

140
Role of ATM
S1
S2
R2
R4
Priority VC Assured VC Best-Effort VC
  • 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

141
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

142
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

143
Internet Timeline 1970s
  • 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)

144
Internet Timeline 1980s
  • 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)

145
Internet Timeline 1980s
  • 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

146
Internet Timeline 1990s
  • 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)

147
Internet Timeline 1990s
  • 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
  • ATT WorldNet becomes the largest pure Internet
    Service Provider

148
Internet Governance
  • Internet Society
  • Internet Activities Board (IAB)
  • Internet Engineering Steering Group (IESG)
  • Internet Engineering Task Force (IETF)
  • Internet Research Task Force (IRTF)

149
IETF Areas
  • Application Area
  • Internet Area
  • Operations Management Area
  • Routing Area
  • Security Area
  • Transport Area
  • User Services Area

150
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

151
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

152
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.

153
References
  • Hobbes Internet Timeline, IETF RFC 2235, Nov.
    1997.

154
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

155
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

156
Part 7 Miscellaneous
157
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

158
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

159
IP Multicast
  • Design and purpose
  • Distributed communication model
  • Class D addresses
  • MBONE

160
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.

161
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

162
RIP Messages
  • Request / Response

Command (Req/Resp)
1
Version
1
reserved
2
Address Family (IP2)
2
reserved
2
Address
4
May be repeated
reserved
8
metric
4
163
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

164
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)
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