section 7 tcpip networking and the internet

IP Networking and the

Internet

Professor Izhak Rubin

[email protected]

Electrical Engineering Department

UCLA

2014-2015 by Professor Izhak Rubin

Internet Architectural

Elements

(c) Prof. Izhak Rubin 3

Internet Architecture and

Protocols

IEEE 802.2, PPP, LAPB, Ethernet, RS232, 802.3, 802.5 Physical/

Link Layer

ARP IP RARP

Type Code

Internet

Layer

Transport

Layer

Upper

Layer

Protocol Number

IGPs

(OSPF)

EGP TCP UDP ICMP IGMP

BGP RIP Port Number

TELNET, FTP, TFTP, BOOTP, HTTP, SNMP, SMTP


Application Protocols: Providing

Service Directly to the user

Hypertext Transfer Protocol (HTTP)

For WWW information retrieval

Simple Message Transfer Protocol (SMTP)

E-mail

TELNET

Remote logon

File Transfer Protocol (FTP)

Reliable file transfer

X-Window system

Graphical interface to applications

Trivial File Transfer Protocol (TFTP)

Simple file transfer

Network File System (NFS)

Remote virtual storage


Application Protocols:

Providing Utility Service

Simple network management protocol (SNMP)

Network management information

Boot protocol (BOOTP) / Dynamic host configuration protocol (DHCP)

Remote loading and configuration capability for diskless workstations

Domain Name System (DNS)

Directory assistance for using names instead of Internet addresses

Address Resolution Protocol (ARP)

Provides a link layer address, given an IP address

Reverse address resolution protocol (RARP)

Provides an IP address, given a link layer address

Inverse address resolution protocol (IARP)

Provides an IP address from a hardware (e.g., DLCI for PVC) address


Illustrative Data Flow using

TFTP/UDP/IP

TFTP

Header

TFTP

Header

TFTP

Header

TFTP

Header

message message message message

UDP

Header UDP

Header UDP

Header

IP

Header

IP

Header

Ethernet

Header

TFTP

Message

UDP

Segment

IP

Datagram

Ethernet

Frame

Call UDP

Call IP

Call Ethernet

Driver

Transmit

on

Bus


Internet Addresses

netid hostid 0

1 0 netid

netid

hostid

hostid 1 1

Class A

Class B

Class C

1 7 24

14 16 (2^16=65,536 hosts/net)

22 8 (2^8=256 hosts/net)

Note: Internet Addresses - Network ID and Host ID

Broadcast address on a net is defined (host id = all 1s)

Address refers to connections (not to hosts)

Routing is based on the Network portion of the address. Address used to a host

determines route.


IP Addressing: An Example

ARPANET

10.0.0.0

ETHERNET 120.10.0.0

120.10.2.4 120.10.2.5 120.10.2.18

120.4.36.4 120.4.36.12

120.4.36.0 120.4.36.7

10.2.0.42 Gateway

HOST Gateway HOST

Token Ring

IP Addressing

Prof. Izhak Rubin


Classes A-C Addresses

Network Address Local Address

Class Network Address

(Bytes)

First Number No. of Local

Addresses

A 1 0-127 16,777,216

B 2 128-191 65,536

C 3 192-223 256

Class D addresses, start with 224-239, for IP multicasting

Class E addresses, start with 240-255, for experimental use

Address blocks reserved for networks not connected to the Internet


Subnets Class A and B network addresses involve organizations that may have many

subnets

Local address = Subnet address + System address

The organization that owns that part of the address is responsible for size

selection and number assignment for subnets

A local address can be broken up at byte boundaries for class A or B address

For a class C address, the local address may be segmented at selected bit

boundary

Network Address Subnet Address System Address

120.118 .48 .123

182.30.36 0011 1101

61

B

C


Subnet Masks Traffic is routed by looking at the network and subnet parts

The subnet field size is selected by an individual organization

For hosts and routers to recognize the subnet boundary, the system must be configured to specify the size of the subnet part

The subnet mask is a sequence of 32 bits

The bits corresponding to the network and subnet parts are set to 1, the system field bits are set to 0.

Example: when the 3rd byte is used for subnet part, the mask is 255.255.255.0

Hosts and routers connected to a subnet are configured with the mask for the subnet.

Example: a network with a large number of point-to-point lines has only 2 systems on each line; may select 14 bit masks 255.255.255.252 (it provides for 16,382 subnets and 2 hosts per subnet)

Reserved addresses: Do not use 0 for subnet or host addresses

All 1s broadcast address on local link. In DHCP, client sends a request to 255.255.255.255 and uses 0.0.0.0 as its source IP address

Use a.b.c.255 to broadcast an IP packet to all nodes in the subnet a.b.c.0, or in network a.b.c.0

Broadcast to entire class B network a.b.0.0. By using a.b.255.255

Thus: A network, subnet or host field cannot consist entirely of 1s or of 0s. Hence, a field must contain at least 2 bits.

Any address that starts with 127 (mostly used 127.0.0.1) is reserved as a loopback address; I.e., local clients communicate via IP within the host.


Supernetting and CIDR A,B, and C class based addressing structure is inefficient.

Class C address yields only 254 usable addresses

An organization given class B address that needs only a few hundreds or thousands of addresses wastes its address space

An organization is assigned only the number of bits that it needs

For example, an organization that needs only 4000 addresses is given 12 bits as local address part. The remaining 20 bits area fixed prefix, used as a new supernetwork or prefix part of the address. The size of this classless network part is /20.

Initial such allocation taken from the available class C address space.

/20 is equivalent to obtaining 16 contiguous class C addresses.

2^12 = 2^8 * 16 = 4096 addresses

To route to an organization, using a single routing table entry, a router needs to know:

No. of bits in the network prefix

The actual network prefix

This is called Classless Inter-Domain Routing (CIDR)

Unused part of Class A numbering space can be divided up in this manner

ISP are provided large blocks of addresses. Provider assigns sub-blocks to its customers. Traffic is routed to the ISP using its block prefix. The provider uses longer prefixes to route to its customers.


Address Resolution Protocol

(ARP)

For mapping Internet Addresses to Physical Addresses; PA = f(IA).

ARP allows a host to find the physical address of a target host on

the same physical network, given only the targets Internet address. The host broadcasts a request on the network. The destination,

recognizing its internet address, responds with its physical address.

A cache is maintained of recently acquired address bindings.

The source host includes in the request its own address binding; this

is recorded by the destination and other hosts. New hosts

broadcast their address binding.

A diskless machine uses its physical address (determined by the

network interface card) to communicate across its network to

receive from a Server its Internet address, at start time. The

protocol used for this communication is called: Reverse ARP

(RARP).


Connectionless Datagram

Networking: The IP Datagram

Datagram Header Data

0 4 8 16 31

VERS LEN TYPE OF SERVICE TOTAL LENGTH

IDENT FLAGS FRAGMENT OFFSET

TIME PROTO HEADER CHECKSUM

SOURCE IP ADDRESS

DESTINATION IP ADDRESS

OPTIONS PADDING

DATA . . .


IP Datagram Fields IP Protocol: connectionless, unreliable, best-effort, packet delivery.

Version (VERS): 4 bits; specifies IP protocol version

Length (LEN): 4 bits; datagram header length (in 32 bit words);

most common header = 20 Octets (LEN = 5)

Total Length: length of IP datagram (in octets, including length of

header and data). Data size computed from Total Length and LEN

fields.

Type of Service: 8 bits; specifies how the datagram should be

handled; has 5 subfields:

PRECEDENCE D T R UNUSED

Precedence - from 0 (Normal) through 7 (Network Control)

D, T, R bits -specifies the type of service the datagram desires:

- D: low delay; T = high throughput; R = high reliability

- A suggestion to the routing algorithm


IP Datagram: Fragmentation

Control

Control of fragmentation and reassembly of packets

Field IDENT - a unique integer that identifies the datagram;

allows destination to collect all fragments from a datagram.

IDENT field plus destination address used for reassembly.

Field FLAG: low order 2 bits (of 3 bits) control fragmentation.

First bit - do not fragment bit (if set to 1); low order bit -

specifies last fragment (fragment with highest offset), also

called - more fragments bit.

Field FRAGMENT OFFSET: specifies the offset of the

fragment in the original datagram (in units of 8 Octets, starting

at offset 0). If one or more fragments are lost, the entire

datagram is discarded.


IP Datagram: Other Header

Fields Time to Live (TTL): species how long (in sec.) the datagram is

allowed to remain in the Internet system. A gateway discards a

datagram if its TTL has expired (reaches 0). Typically, each

transfer is taken to last for 1 unit of time, and each gateway

decrements the TTL by 1 (yielding hop length control).

Field PROTO: Specifies the format and contents of the data by

identifying the higher level protocol type.

Field HEADER CHECKSUM: ensures integrity of Header

values.

SOURCE and DESTINATION IP Addresses: 32 bits Internet

addresses.

PADDING: Octets containing 0, to ensure the header extends

to an integral multiple of 32 bits (note that header length field is

specified in terms of 32 bit words).


IP Datagram: Options OPTIONS: not required in every datagram; used mostly for network testing or

debugging. Variable length field:

Copy (1bit)+Option Class(2)+Option Number(5).

Option Class 0: Datagram or network control

Option Class 2: Debugging and measurement

Record route Option: Source arranges that each gateway that handles the

datagram adds its name to a list of IP addresses.

Source Route options:

The sender specifies a path across the Internet; e.g...; to test a route.

Strict source routing: includes a sequence of Internet addresses, with the path

between 2 successive addresses consisting of a single physical network

Loose source routing: a sequence of Internet addresses; multiple network hops can

exist between successive addresses.

Time Stamp option: recording of time (in msec since midnight) by each gateway

along a specified list. Used for performance monitoring and evaluation.


Routing IP Datagrams

THE INTERNET IS COMPOSED OF MULTIPLE PHYSICAL NETWORKS INTERCONNECTED BY GATEWAY COMPUTERS.

HOSTS CONNECT DIRECTLY TO ONE OR MORE PHYSICAL NETS Both Hosts and gateways participate in IP routing. Host with multiple network

connections can act as gateways.

Direct Routing:

Uses directly the underlying physical transmission system. No gateway is used.

Datagram is encapsulated in the physical frame and maps the IP address to a

physical address (using address resolution methods such as ARP on shared

medium nets) The Internet address of the destination reveals whether it is on the

same physical net as the source.

Indirect Routing: The destination is not located on a directly attached network; the datagram is first passed to a gateway for delivery.

Datagrams are passed from gateway to gateway until they reach a final gateway

which delivers then directly.


Table Driven IP Routing

Internet Routing Table used at each switching node.

When a datagram arrives at a gateway, IP extracts the destination

Internet address, obtains the network portion, and uses it to make

routing decisions. In this manner, just the structure of the gateway

network is used, and a gateway does not need to store a too large

Table (destination net and not destination host address is used for

routing!)

Routing table contains pairs (N,G), where N = Destination Network

address, G = Internet address of Gateway to which to send

datagrams destined to N. G can be reached directly from the

source.

Per destination Host specific routes can also be configured.

Default routes are use at times.


Illustrative Routing Table: RIP

Router - 1


Illustrative Routing Table: RIP

Router - 2


Illustrative Routing Table: IGRP /

BGP Router - 1


Illustrative Routing Table: IGRP /

BGP Router - 2


Internet Control Message

Protocol (ICMP)

ICMP - a required part of IP, used to report errors, to send control data, and

to provide information about unexpected conditions.

ICMP information is transported in the Data portion of IP Datagrams; used

by Internet software on destined machine (gateway or host).

Every ICMP message starts with a Type field (8 bits) and CHECKSUM (16

bits)

ICMP messages reporting error contain the IP header and the first 64 bits of

the datagram causing the error (these bits may contain higher level protocol

info).

ICMP Echo request message: used to test whether a destination is alive

and reachable. A machine receiving such a request must formulate an echo

reply, returning the same data as in the request.

Destination Unreachable ICMP message: message sent by a gateway to

the original source when it cannot deliver an IP datagram. A Code field is

used to further describe the problem: unreachability by network, or host, or

protocol, or port; fragmentation needed and DF set; source route failed.


Other ICMP Messages

ICMP source quench message: gateway requests source to

slow down. The source lowers its sending rate until its stops

receiving such requests; it can then gradually increase its rate.

ICMP redirect message: used by gateway (which receives

route update by communicating with other gateways) to inform

a host that it uses a non-optimum route. Limited to interaction

between a gateway and a host on a directly connected network.

ICMP time exceeded message: sent by gateway when a

datagram is discarded since it has exceeded its hop count (the

letter reaches 0 at this gateway). Also used by host to report

that fragment reassembly time exceeded.

ICMP parameter problem message: sent by a gateway or

host when it finds a problem with the datagram header and

therefore must discard it.


Additional ICMP Messages

ICMP time stamp request and reply messages: reply

contains originate, receive and transmit timestamps.Round trip

delay and the differences in the clocks can then be estimated.

ICMP information request and reply message: used by a

machine to obtain an Internet address for a network to which it

is attached. (An alternative to RARP.)

ICMP Address Mask request and reply messages: to obtain

an address mask.

Subnet Addressing Mask:

Subnet addressing allows multiple physical networks to share a

single IP network address.

A Subnet Mask (32 bits) is used to identify which bits in the Internet

address correspond to the underlying physical network.


TCP/IP Internet Layering Model

Application

Transport

Internet

Network Interface

Hardware

Messages / Streams

Transport Protocol Packets

IP Datagrams

Network Specific Frames

Note: Transport Reliability control is performed by the Transport protocol on an

end-to-end basis. Corrupted datagrams are discarded by intermediate gateways.


User Datagram Protocol (UDP)

UDP provides for a connectionless transport service - multiple

applications executed on a given host can send and receive

datagrams independently.

Processes on a machine are identified by protocol ports.

Operating systems schedule and queue messages that wish to

access ports and processes which wish to extract data from a

port. Source and destination ports are specified to allow for a

two-way interchange.

Using UDP, senders can distinguish between multiple recipients

on a single machine.

UDP depends on the Internet protocol for UDP message

transfer - hence providing unreliable, connectionless delivery

service. No ACK, no ordering and no feedback rate control.


UDP Message Format

UDP Header UDP Data

UDP Header - Four 16-bit fields:

Source Port Destination Port

Length UDP Checksum

0 16 31

Length: Count of Octets in the UDP datagram, incl... header and data (Min =8,

header alone).

UDP Demultiplexing: UDP datagrams accepted from the IP software are demultiplexed

based on their specified UDP port.

Universal (well known) port assignments: performed by a central authority

Port assignments by dynamic binding by net software and obtained by request & reply.

Internet assigns few port numbers apriori (255 ports), while most are left for local sites or

application programs.


Transmission Control Protocol

(TCP): Features TCP provides a reliable stream transport layer service.

Key features:

1. Stream integrity - stream of bits / bytes passed in sequence to the destination

(ordered delivery)

2. Virtual Circuit Connection (VCC): call placed, connection set-up by the

corresponding software modules in the 2 operating systems; once a connection is

set-up, the application programs are informed and the transfer can start.

3. Buffered Transfer. Bytes received from the application can be buffered and

collected to make longer transport PDUs. A push force by the sender can be used to force immediate transfer without waiting to fill the buffer. At the receiver, it

is made available to the application without delay.

4. Unstructured Stream. The stream structure does not affect transfer service.

5. Full Duplex Connection. Concurrent transfer in both directions is allowed.


TCP Functions As for UDP, TCP ports are used to connect to multiple applications.

Demultiplexing among multiple applications can be used. A connection

must be set-up by the operating systems prior to transfer

The stream units TCP operates on are Octets (Bytes). These are

divided into segments. Usually, each segment is carried in a single IP

datagram.

A sliding window mechanism, using PACK + Timeout procedure, is

used for error control and flow control. It operates at the Byte level.

TCP allows the window size to vary over time. Each ACK, which

specifies how many Bytes have been received, contains a window

advertisement specifying how many additional bytes the receiver is

willing to accept. In this manner, dynamic flow control is implemented,

adapting to the current buffer availability at the receiver.

Piggyback ACK is used.


TCP Segment Format

0 4 8 16 31

SOURCE PORT DESTINATION PORT

OPTIONS PADDING

DATA . . .

. . .

DATA . . .

SEQUENCE NUMBER

ACKNOWLEDGEMENT NUMBER

OFF. RES. CODE WINDOW

CHECKSUM URGENT POINTER


TCP Segment Fields

TCP Header + Data fields

Source and destination port numbers identify the application programs

at the connection ends

Sequence Number - position of byte stream of the data in the segment

ACK Number - position of the highest Byte received by the source

Offset - an integer which specifies the offset of the data portion of the

segment; note that options field varies in length

CODE - determines the purpose and contents of the segment;

indicates how to interpret the subsequent header fields. Segment may

carry an ACK, Data, be a request to establish or close a connection,

etc.

WINDOW - used by TCP to advertise how much data it is willing to

accept by specifying its buffer size

Urgent - high priority data indicated; notify application to enter urgent mode. (Such data is called at times out of band data)


TCP Segment Fields - Cont. Options field - used to communicate with the TCP software at the other end

of the connection. Can be used to specify Max Segment Size it is willing to

receive.

Small segment size can lead to overhead & throughput inefficiencies; about 40

Bytes are used for IP and TCP headers, so that a 1 Byte data field leads to

throughput level of only 1/40.

Too large segment sizes can lead to performance degradations. Large datagrams

may be fragmented for the transmission across the Internet. Fragments are not

independent - all must arrive, otherwise all have to be retransmitted. Hence, when

fragments can be lost, when the segment size is > fragment length, throughput

degradations can occur.

TCP Checksum - to verify integrity of TCP segment header and the data

ACKs - specify the number of the next byte that the receiver expects to receive (stream

and not packet based) - cumulative ACK.

ACK timeout estimates can be performed dynamically based on current round trip

delay observations (new one is weighted by q


TCP Connection

Connection establishment - by 3-way handshake. Connection

is set-up as full duplex. Initial sequence numbers are then

agreed on.

Connection closing. One direction can be closed before the

other.

Push operation used to force transmission of data. A PSH bit

is set to force receiver to deliver data to the application. e.g..,

used push function after each keystroke at an interactive

terminal.

Urgent indicator used for high priority transfer.

Reserved and unreserved TCP port numbers.


IPv6: The Header Ver. Prio. Flow Label

Payload Length Next Header Hop Limit

Source Address

Source Address

Source Address

Destination Address

Destination Address

Destination Address

Destination Address

Source Address

IPv6 Notes

Internet Protocol version 6 (IPv6) is a version of the Internet Protocol that is designed to succeed IPv4, the first

publicly used implementation, which is still in dominant use currently. It is an Internet Layer protocol for packet-

switched internetworks. The main driving force for the redesign of Internet Protocol is the foreseeable IPv4

address exhaustion. IPv6 is specified by the Internet Engineering Task Force (IETF) and described in Internet

standard document RFC 2460, which was published in December 1998.

IPv6 has a vastly larger address space than IPv4. This results from the use of a 128-bit address, whereas IPv4

uses only 32 bits. The new address space thus supports 2128 (about 3.41038) addresses. This expansion provides

flexibility in allocating addresses and routing traffic and eliminates the primary need for network address translation

(NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion.

IPv6 also implements new features that simplify aspects of address assignment (stateless address

autoconfiguration) and network renumbering (prefix and router announcements) when changing Internet

connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion

of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from Link Layer media

addressing information (MAC address).

Network security is integrated into the design of the IPv6 architecture. Internet Protocol Security (IPsec) was

originally developed for IPv6, but found widespread optional deployment first in IPv4 (into which it was back-

engineered). The IPv6 specifications mandate IPsec implementation as a fundamental interoperability

requirement.

In December 2008, despite marking its 10th anniversary as a Standards Track protocol, IPv6 was only in its

infancy in terms of general worldwide deployment. IPv6 has been implemented on all major operating systems in

use in commercial, business, and home consumer environments.

(c) Prof. Izhak Rubin 39 Reference: Wikipedia, Sept. 2010

An Illustrative IPv6 Address (in

hexadecimal and binary)


The size of a subnet in IPv6 is 264 addresses (64-bit subnet mask), the square of the size of the entire IPv4 Internet. Thus, actual address space utilization rates will likely be small in IPv6, but

network management and routing will be more efficient because of the inherent design decisions

of large subnet space and hierarchical route aggregation.

When first connected to a network, a host sends a link-local multicast router solicitation request for its configuration parameters; if configured suitably, routers respond to such a request with a

router advertisement packet that contains network-layer configuration parameters.[12]

If IPv6 stateless address autoconfiguration is unsuitable for an application, a network may use stateful configuration with the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) or hosts

may be configured statically.

Routers present a special case of requirements for address configuration, as they often are sources for autoconfiguration information, such as router and prefix advertisements. Stateless

configuration for routers can be achieved with a special router renumbering protocol.

Reference: Wikipedia, Sept. 2010

Routing Simplifications in IPv6

The packet header in IPv6 is simpler than that used in IPv4, with many rarely used

fields moved to separate options; as a result, although the addresses in IPv6 are four

times larger, the option-less IPv6 header is only twice the size of the option-less IPv4

header.

IPv6 routers do not perform fragmentation. IPv6 hosts are required to either perform

PMTU discovery, perform end-to-end fragmentation, or to send packets no larger

than the IPv6 default minimum MTU size of 1280 octets.

The IPv6 header is not protected by a checksum; integrity protection is assumed to

be assured by both a link layer checksum and a higher layer (TCP, UDP, etc.)

checksum. (UDP/IPv4 may actually have a checksum of 0, indicating no checksum;

IPv6 requires UDP must have its own checksum.) Therefore, IPv6 routers do not

need to re-compute a checksum when header fields (such as the TTL or Hop Count)

change. This improvement may have been made less necessary by the development

of routers that perform checksum computation at link speed using dedicated

hardware, but it is still relevant for software based routers.

The Time-to-Live field of IPv4 has been renamed to Hop Limit, reflecting the fact that

routers are no longer expected to compute the time a packet has spent in a queue.



IPv6 Simplifications

Fixed format headers

extension headers used

Header checksum removed

Note that encapsulation procedures include a packet checksum; checksums

also used at the MAC frame layer and ATM adaptation layers

Removal of hop-by-hop segmentation procedure

No fragmentation in the Internet; end-to-end fragmentation; path MTU

discovery used to establish MTU

Transmission of large packets which are segmented into small segments

can result in excessive retransmissions and throughput degradation; hence,

no segmentation used

IPv6 networks are required to carry a payload of 536 Octets; when no

discovery used, small packets can be sent.

Removal of Type of Service field, which indicates preference for path

selection. IPv6 provides mechanisms for handling such preferences.


IPv6 Header Parameters

Payload length; length of the data carried after the header (which contains

40 Bytes)

Next header type; e.g..; UDP or TCP; or Extension Header.

Hop limit; counts the number of hops.

New fields; facilitate handling of realtime traffic:

Priority (16 levels)

Flow Label; used to distinguish packets which require the same treatment.

Extension Headers; arranged in a daisy chain; includes:

Hop by hop options header

Routing header

Fragment header

Authentication header

Encrypted security payload

Destination options header


Extension Headers

Routing Header; consists of a set of parameters followed by a list of addresses, used for

source routing (strict or loose sense)

Fragment header; for end-to-end fragmentation; a fragment header is inserted in each

fragment packet between the IPv6 header and the payload. Each fragment is routed

independently. The fragment header contains information allowing the destination to

concatenate the fragments. (Fields: Next header, Fragment Offset, M, Identification.)

Destination Options header; options header contains an option field in which option data

can be inserted. Each option is identified by an Option Type No.

Hop by Hop options; e.g..; jumbo payload option: since a 16 bit payload length field is

used, the max payload length is 64 KB. For longer packets, this option is used,

providing a 32 bit packet length field.

Extension header order; recommended: IPv6 header;Hop by hop options; destination

options (1); routing; fragment; authentication; destination options (2); upper layer headers (such as TCP, UDP)

IPv6 Header

Next Header=Routing

Routing Header

Next header=TCP TCP Header + Data


ICMP Evolution

Format: type, code, checksum (ICMP packet and fixed fields of

the IPv6 header), variable length body.

14 different types currently defined: destination unreachable;

packet too big; time exceeded; parameter problem; echo

request; echo reply; group membership query , report and

termination; router solicitation and advertisement; neighbor

solicitation and advertisement; redirect.

Error ICMP packet are not generated for multicast packets (can

create avalanche) and not in response to ICMP packets.

Reassembly timer is set at start of packets reassembly of fragments; timeout levels of 1-2 minutes can be set.

Echo request and reply serve as IPv6 Ping.


IPv6 Specification Issues

8 bit hop count - 255 hops. Hop count used to prevent

long looping of packets.

16 bits length field - 64 KB packets. Segmentation of

large messages into 64KB packets induces only

40B/64KB = 0.06% overhead. Jumbogram option field

can be used to code a jumbo packet length using 32 bits

field. This is hop by hop option which is acceptable for

supercomputers (mostly directly connected).

No checksum used in IPv6.


Address Architecture Increasing the address length from 32 bits to 128 bits allow the use of more degrees of

hierarchy, beyond the basic IPv4 layers of: Network, Subnet, Host

The address identifies an interface connected to a subnetwork, not a station. A

multihomed station will have as many addresses as interfaces. IPv6 allows an interface

to be identified by several addresses to facilitate routing or management.

IPv6 address categories: Unicast, Multicast, Anycast. Anycast address indicates that

the packet should be delivered to the nearest member of the group.

Address Notation: Eight 16-bit integers separated by colons; each integer is

represented by hexadecimal digits. e.g..; BC95:FEBD:6574:432A: etc..

Prefixes used for addresses employed by selected entities; e.g.., provider based

addresses. This consists of the following IDs: registry, provider, subscriber, subnetwork, interface.

Special addresses: Unspecified; Loopback; IPv4; Site local (not sent on the Internet;

incl.. IDs for subnet and station); Link local (for stations on the same link; incl.. station ID; not handled by a router).


Interdomain Routing Routing Tables become very large if an entry is maintained for every network

in the Internet.

To reduce routing table size, we must aggregate several routing entries.

Hence, construct an hierarchy of addresses and use interdomain routing.

IPv6 solution: use provider addresses; they have a good relation with the

networks topology (geographical and organization based boundaries can be ineffective).

Routes exchanged through the Interdomain Routing Protocol (IDRP).

For current IPv4, growth of routing tables is dealt with by deploying Classless

Interdomain Routing (CIDR). Within CIDR, IPv4 addresses are not

considered as composed of fixed length network numbers, but replaced by

variable length prefixes.

For IPv6, a station can have multiple addresses associated for interface to

networks run by multiple providers. Connection/packets can use any of these

networks.


Interdomain Routing: BGP-4

to IDRP IPv4 Internet is an autonomous system, consisting of a collection of

subnetworks managed by a single entity. For example, a network provider

network, or that of a large company.

Autonomous systems use Exterior Gateway Protocol (EGP) to exchange

reachability information, to describe the destination. The Exterior Gateway

Protocol (EGP) was defined in 1982 and has been gradually replaced by

successive versions of the Border Gateway Protocol (BGP).

BGP-4 supports the routing table aggregation required by CIDR. It is a path

vector protocol. Border routers (linking 2 adjacent autonomous systems)

are allowed to announce paths. BGP is optimized for 32 bit addresses.

The Exterior Gateway Protocol (EGP) used by IPv6 is not based on BGP but

on IDRP (which is part of the OSI model). It is also in the path vector family,

and allows the use of multiprotocol routing and compute routing tables for

several families of addresses.

BGP messages are exchanged over TCP, while IDRP PDUs are carried over

a datagram service. IDRP runs directly on top of IPv6.


Intradomain Routing An interior routing protocol is used to compute routes and maintain connectivity within a

routing domain or an autonomous system.

For the current Internet, domain managers have to chose an IGP. Updated version of

IPv4 protocols are composed: updated OSPF and RIP. Other: IS-IS, EIGRP.

OSPF (Open Shortest Path First) is the recommended protocol for intra-domain routing.

It is a link state protocol. All routers maintain a copy of a data base which contains link

state records (containing the status of links in the network area of interest). OSPF can

run on top of IPv6 between IPv6 capable nodes. The corresponding IPv4 OSPF can

operate in parallel (no integration).

RIP is a distance vector type routing protocol. Metric pairs used to describe reachable

destinations. Path length is identified in terms of the hop length (so that link status

identifiers., incl.. throughput and delay parameters, may not be included). Simpler to

implement but not as efficient. Can be used in small areas or for simple networks.

RIP for IPv6 is a simple update of RIP for IPv4. Requests sent to trigger an immediate

response about a destination status; responses sent every 30 sec to all neighbors.

Metric field contains the no. of hops required to reach a destination. RIP messages

exchanged in UDP datagrams.


Other Routing Protocols

Dual IS-IS is an extension of the routing protocol defined for CLNP in the

OSI Suite. It is a line state protocol, trying to perform integrated routing. A

single data base describes the links between all the routers in the network.

Included is also protocol specific addressing information. Dual IS-IS is able

to handle CLNP with IPv4. Extension to IPv6 defined.

IGRP (Cisco) - has an extended version EIGRP. It is capable of supporting

several network protocols in parallel, as IS-IS.

Notes: Some believe that routing should be tied with flows; resource

reservation can then be applied across a flows path to effectively support realtime applications. Assign a route based on current congestion levels so

that the required QOS level is attained. A source route (derived from map

servers) will require high addressing overhead (128 bits for each

intermediate router). Alternative: VC route and VCIs - a flow setup model. But this is an approach which is completely different than the Internets scheme, and has yet to be proven.


Address Resolution: Neighbor

Discovery Process

The neighbor Discovery Process is used by IPv6 for address

resolution, to determine the subnet or media address of the destination

station. It includes and replaces the IPv4 ARP and route discovery.

It is defined as part of IPv6 ICMP. Initially, messages are sent to

multicast addresses. For IEEE 802 family (incl.. Ethernet or FDDI), a

48 bits multicast address is obtained.

If destination is not local, the first hop will be to a neighboring router.

The media address of this router is either already known (from past

use, and is cached), or it is obtained by sending a neighbor solicitation

message (which is an ICMP multicast address).

For access through Non-Broadcast Multiple Access (NBMA) network,

such as ATM or X.25 or circuit-switched network, it is not feasible to

multicast neighbor solicitation messages. Rather, the host is

configured with the ATM address of at least one router. It can then

send solicitations to this router, and receive router advertisements in

responses. The preferred router will be taken by the host as the next

hop.


Realtime Support and Internet

Flows To support realtime applications, a flow is defined; the IPv6 header

fields of flow label and priority class are used.

A flow is a sequence of packets sent from a particular source to a

particular (unicast or multicast) destination for which the source

desires special handling by the intervening routers.

Packets making a flow have the same source-destination stations and

the same 24-bit flow label. Null flow labels are used when flows are

not designated by the application (as by current SMTP mailers, FTP

file transfers and HTTP web browsers). To be used by applications

with strict realtime objectives.

The flow label may be used in conjunction with the routing header: a

source route can be defined; all packets (through belonging to multiple

applications and multiple streams) using this route will require special

processing.

Flows are not equivalent to virtual circuits; the labeling of flows does

not affect routing.


Realtime Support:

Reservations

Flow labels can be used with resource reservation to ensure

that resources are pre-allocated at the nodes to support

realtime streams; datagram packet switching does not support

well hard realtime applications such as video or voice transfers.

Example: packet voice - 64 Kbps PCM, with packets containing

160 samples, or 20 msec of voice. Rate = 50 packets/sec sent

through the Internet. Quality drops as the network becomes

congested. Delay variances induce long playback delays

(reducing interactivity); packet losses result in crackles.

Use reservations to configure the queueing and scheduling of

designated packets at the network nodes. Such a resource

reservation protocol: RSVP. IPv6 labeling is used in

conjunction with this protocol.


Reservation and Scheduling

Reservation procedure is used to declare the realtime flows

and to inform the routers as to their resource requirements.

In front of the outgoing interface of a router, each realtime

stream is provided its own queue. All other traffic shares a

data queue. A realtime queue is served at its requested rate, thus regulating its packet delays. The data queue is served

on a best effort basis. R1

R2

Data

Server


Multimedia Over the Internet Recent Internet approaches: Fair queueing methods employed in contrast with

reservations, combined with class based queueing. Use of hierarchical encoding.

Adaptive operations:

In 1988, the use of slow start for TCP (Van Jacobsen). Start at slow rate and increase rate

gradually. Include a feedback loop that slows down the application if the network becomes

congested. Problems with multi-media open loop applications.

Video quality can be traded with network congestion - adaptive rate regulation.

Adaptive voice (and video) encoding - use embedded encoding and congestion based no.

bits/sample (recent papers by I.Rubin and K.K. Chang)

Hierarchical encoding uses the IPv6 priority field: Bits 0-7 for congestion controlled traffic (7 =

highest priority, for control traffic); bits 8-15 for realtime traffic (15=highest priority)

Fair queueing: the server allocates its resources to each user in a fair manner. For example, by

queueing the packets of each active user in separate queues and serving them in a Round Robin fashion. No explicit reservations need be used. Different queueing classes can be defined (e.g.., a class per destination, per source, per TCP connection, etc..). Resources can be reserved for a queueing class,

and fair queueing used to share resources within a class. Leads to schemes: Processor Sharing (PS);

generalized Processor Sharing (GPS). But to relate QOS with allocated resource, source traffic (flow)

needs to be policed.

section 7 tcpip networking and the internet

Documents

pvc address c

izhak rubin c

subnets local address

internet c

subnet address system

local address ca

internet professor izhak

host id broadcast address