Feb.2001 C.Watters

NAMES and ADDRESSES

What’s in a name, anyway?

1011010011001110000111001100110

Feb.2001 C.Watters

Internet Node Addresses

Each node has unique network name

hierarchical composition based on name granting authority

www.cs.dal.ca unique network address

hierarchical composition based on topographical

129.173.66.61

Feb.2001 C.Watters

How do we get the network addr from network name?

Network server translates name to locationNeeds to do a “lookup”“lookup” directories are distributed!! Grouped into domains based on names each domain has a local name server

process if fails to find match, forwards request up

the line

Feb.2001 C.Watters

Domain Hierarchy

DNS hierarchy can be viewed as a tree Node in the tree corresponding to a

domain. Leaves in the tree corresponding to the

host being named.

DNS names are processed from right to left and use period as separator.Example:

Feb.2001 C.Watters

Domain Hierarchy

edu com gov mil org net uk ca

arizona….mit acm ieee

cs ece physics

bas che opt

Feb.2001 C.Watters

Name Server

Domain name hierarchy is partitioned into subtrees called zonesZone: Corresponds to some administrative authority responsible for that portion of hierarchyZone is the fundamental unit of implementation of a name server.DNS can be thought of as a hierarchy of name servers.

Feb.2001 C.Watters

Name Server

Root name server

Arizona name server

Bellcore name server

…...

Cs name server

ECE name server

Feb.2001 C.Watters

Name Server

Resource records: Name-to-value binding <Name, Value, Type, Class, TTL> Type field specifies how the Value should

be interpreted. A: indicates that the value is a IP address. NS: the domain name for a host that is

running a name server that knows how to resolve names within the specified domain.

CNAME: the canonical name for a particular host

MX: domain name of host running mail server

Feb.2001 C.Watters

Name Server

Class: allows entities other than NIC to define useful record types. Widely used one - INTTL: shows how long this records is valid.Example of resource records: Root name server contains an NS record for

each second level server. It also has an A record that translate this name into IP address.

<arizona.edu, telcom.arizona.edu, NS, IN> <telcom.arizona.edu, 128.196.128.233, A, IN>

Feb.2001 C.Watters

Name ServerSecond level

<cs.arizona.edu,optima.cs.arizona.edu, NS, IN><optima.cs.arizona.edu, 192.12.69.5, A, IN>

<ece.arizona.edu, helios.ece.arizona.edu, NS, IN><helios.ece.arizona.edu, 128.196.28.166, A, IN>

Third level (within NS)<optima.cs.arizona.edu, 192.12.69.5, A, IN><cheltenham.cs.arizona.edu, 192.12.69.60, A, IN>

Feb.2001 C.Watters

Name Resolution

ClientLocal name server

Root name server

Arizona name server

CS name server

cheltenham.cs.arizona.edu

1 cheltenham.cs.arizona.edu

2

Arizona.edu, 128.196.128.233

cheltenham.cs.arizona.edu

Cs.arizona.edu, 192.12.69.5cheltenham.cs.arizona.edu

cheltenham.cs.arizona.edu,

192.12.69.60

192.12.69.60

3

4

5

6

7

8

Feb.2001 C.Watters

What is the network IP address?

32 bits (4 bytes) per node

schemes class-based addresses subnet addresses CIDR addresses classless addresses

Feb.2001 C.Watters

1.Class-based AddressingGeneral form network.hosteg. UC Berkeley is 128.32.0.0 2 bytes with decimal values 128 and 32 1000 0000 = 128 and 0010 0000=32

eg. Borg 129.173.66.61 4 bytes with dec. values 129 173 66 and 61 1000 0001=129 etc

large networks have small addresses (more room for hosts on them) & small networks have longer address (fewer hosts expected)

Feb.2001 C.Watters

Classes

Class A - large networks (net 1 byte/host 3)

Class B - medium networks (net 2 bytes/host 2)

Class C - small networks (net 3 bytes/host 1)

1 0

1 1 0

host

host

host

Network

Network

Network

0

Feb.2001 C.Watters

Example

140.179.220.200

140 179 220 20010001100 10110011 11011100 11001000

Feb.2001 C.Watters

Look again at binary addresses????

A 1 byte network number starting with 0 0111 1111 is the biggest number 1-126 are A network addresses (126/16M hosts) written as 126.hostbyte1.hostbyte2.hostbyte3

A 2 byte network number starting with 10 1000 0000 0000 0000 so starts 128 1011 1111 1111 1111 up to 191 written as 129.173.hostbyte1.hostbyte2

(16k/64k hosts)A 3 byte network number starting with 11 1100 000 000 0000 0000 0000 starts 192 up to

223 written as 198.174.66.hostbyte (2M/256 hosts)

Feb.2001 C.Watters

So What’s the Problem

Class A network ID – 16 M hosts!!Class B network ID – 65k hosts

Hosts with same network ID are in same broadcast domain – IP routerMost of these addresses are wastedDanger of running out of IP addresses

Feb.2001 C.Watters

2.Subnet Addressing

Create smaller broadcast domainsBetter use the bits in the host IDSubnetting allows a large network, say a class B network, to split into subnets each bounded by an IP routernow say x subnets each of y nodes can share the one class B address (instead of using x class B addresses.)

Feb.2001 C.Watters

Subnet Network IDs

Subnet has its own network IDThis ID is a subset of the original class-based network IDa mask is used to identify which bits of the HOST portion are subnet ID and which the actual host

Feb.2001 C.Watters

Example

Network 139.12.0.0 to rest of the Internet

Sub Networks local router uses these ID’s 139.12.1.0 139.12.2.0 139.12.3.0

Feb.2001 C.Watters

So what are subnet masks??

Subnet mask is used so that the local router can extract the subnetted network IDsubnet mask shows which bits of host ID are subnet

bits and which host bits 32 bits long - goes with the network

address router ANDs bits together to find subnet

address 1- network ID & 0- host ID

Feb.2001 C.Watters

Subnet example

<network ID><Host ID><network ID><Subnet ID><Host ID>IP address 128.32.134.56 & mask 255.255.255.0128 tells us this is a class B address so network part is 128.32

mask is 11111111 11111111 11111111 00000000 AND these together to get the subnet address

so use first 24 bits as the subnet address!! And last 8 bits are for the host

Feb.2001 C.Watters

Why Bother?

Turns out this uses addresses more efficiently within networks Addressessource computers can find out if the destination computer is on the same subnet or whether it needs to go out to the router

Feb.2001 C.Watters

3. CIDR (Classless Interdomain Routing)

For most organizations Class C address is too small (254) Class B address is too big (16k)

CIDR assign a range of 8 Class C addresses – 2000 hostsProblem – routers now need to recognize multiple IP addresses!!CIDR collapses set of Class C addresses into one!

Feb.2001 C.Watters

How does CIDR work?Routing table entry Starting class C address Plus number of addresses allocated using

a subnet mask

Example Start 220.78.168.0 End 220.78.175.0 11011100 01001110 10101000

00000000 11011100 01001110 10101111

00000000 SO 220.78.168.0/21 is the CIDR block

Feb.2001 C.Watters

4.Classless Domain routing

Addresses are prefix-freeinitial segment can define a domain IF shortening it does not define another domain 01 10 11

routing table has longest matching prefixes

Feb.2001 C.Watters

An exampleStill can have domains194.23.17.4Let 1st 3 bits designate continent next 7 bits country France may use 5 bits for town Belgium may use only 4 bits for townusing all 32 bits as address get 4 billion host addresses

Feb.2001 C.Watters

IPv6

Feb.2001 C.Watters

Why do we need a new version IP?

IPv6 features

Feb.2001 C.Watters

Why do we need a new version IP?

With rapid explosion of destinations, we are on the wayto exhausting the available Internet addresses

Feb.2001 C.Watters

Network Host Growth Rate

Feb.2001 C.Watters

What? There are lots of addresses!!

Addresses are used in host blocks and cannot be used by other hostsMillions of addresses are unused and unusable!

Feb.2001 C.Watters

IPv6 Feature

128 bits address spaceAdvanced Routing CapabilityBetter Options Support Better Quality of service SupportAuthentication and Security

Feb.2001 C.Watters

A, B, C class of IPv4 address

Class prefix scope network ID host ID subnet mask A 0 1-126 x. x.x.x 255.0.0.0

B 10 128-191 x.x x.x 255.255.0.0

C 110 192-223 x.x.x. x 255.255.255.0

0.0.0.0 reserved for broadcasting

127.0.0.1 reserved for loopback

224-255 reserved for multicast and research

Total about 4 billion IP addresses

Feb.2001 C.Watters

IPv6 address architecture

128 bits of address spacerepresentation of address

address format x:x:x:x:x:x:x:x (hexadecimal)

56DF:C4CC:A44B:5528:8E52:4224:ACBB:01EE special syntax CDFA:0000:0000:0000:0000:0000:11E7:D45A =CDFA::11E7:D45A

3.4 x 10^38 addresses,

Feb.2001 C.Watters

prefix of IPv6 address

prefix reserved for IPX address 0000 010 reserved for NSAP address 0000

001 reserved for multicast address 1111 1111

unassigned address 101 …… ……

Feb.2001 C.Watters

IPv4 address transits to IPv6

IPv4-compatible IPv6 address80 bits 16 bits 32 bits

0000…0000 0000 IPv4 address

Reference: RFC1881, RFC1887, RFC1924

Feb.2001 C.Watters

IPv6 Header is simpler:

Header of IPv6Header of IPv4

IPv6 increases the length of the IP header from 20 bytes to 40 bytes, but IPv6 header contains fewer fields, thus, it speed up routing.

Feb.2001 C.Watters

Flow Label Field in IPv6

Version: The version number of the protocol, 6 for IPv6 and 4 for IPv4.IPV6 introduce flow label to mark the packets requiring special handling(such as video and audio).Type of Service in IPv4 indicate how important the packet is.

Feb.2001 C.Watters

Identification, Fragmentation Flags and Fragment Offset

Fragmented packets have an extension header rather than fragmentation information in the IPv4 header. This reduces the size of the basic IPv6 header.

Since higher-level protocols, particularly TCP, tend to avoid fragmentation of packet, this reduces the IPv6 header overhead for the normal case. IPv6 does not fragment packets in router to their destinations, only at the source.

Fields removed from IPv6

Feb.2001 C.Watters

Fields removed from IPv6 (continued)

Header Checksum Because transport protocols implement checksums, and because IPv6 includes an optional authentication header which can also be used to ensure integrity, IPv6 does not provide checksum monitoring of IP packets.

Both TCP and UDP include a header in the checksums they use, so in these cases, the IP header in IPv4 is being checked twice.

Feb.2001 C.Watters

Summary

IPv6 simplifies packet header formats.

IPv6 provides a much larger address space

IPv6 supports authentication and encryption of packet contents at the network layer.

Feb.2001 C.Watters

Transition Planning Options

Maintain complete IPv4 routing system until run-outUpgrade IPv4 router to IPv4/6 dual routerBuilding up IPv6 only routing system 6-bone

Shutdown IPv4 in areas where there is no need for IPv4