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 location
Needs to do a “lookup”
“lookup” directories are distributed!!
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Feb.2001
Grouped into domains based on names
each domain has a local name server process
if fails to find match, forwards request up the line
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
arizona….mit
cs ece
bas che
Feb.2001
acm
physics
opt
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org
ieee
net
uk
ca
Name Server
Domain name hierarchy is partitioned
into subtrees called zones
Zone: Corresponds to some
administrative authority responsible for
that portion of hierarchy
Zone is the fundamental unit of
implementation of a name server.
DNS can be thought of as a hierarchy of
Feb.2001 name servers. C.Watters
Name Server
Root name server
Arizona name
Bellcore name
…...
server
server
Cs name
server
Feb.2001
ECE name
server
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 - IN
TTL: shows how long this records is valid.
Example of resource records:

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Feb.2001
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>
C.Watters
Name Server
Second 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
2
1
cheltenham.cs.arizona.edu
Client
192.12.69.60
8
Local
name
server
3
cheltenham.cs.arizona.edu
Cs.arizona.edu, 192.12.69.5
4
5
Root
name
server
Arizona
name
server
6
7
Feb.2001
C.Watters
CS
name
server
What is the network IP
address?
32 bits (4 bytes) per node
schemes
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Feb.2001
class-based addresses
subnet addresses
CIDR addresses
classless addresses
C.Watters
1.Class-based Addressing
General form network.host
eg. 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)
0 Network
host
Class B - medium networks (net 2 bytes/host 2)
host
1 0 Network
Class C - small networks (net 3 bytes/host 1)
110
Feb.2001
Network
host
C.Watters
Example
140.179.220.200
140
179
220
200
10001100 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
C.Watters
 Feb.2001
written as 198.174.66.hostbyte
(2M/256 hosts)
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 router
Most of these addresses are wasted
Danger of running out of IP addresses
Feb.2001
C.Watters
2.Subnet Addressing
Create smaller broadcast domains
Better use the bits in the host ID
Subnetting allows a large network, say a class
B network, to split into subnets each bounded
by an IP router
now say x subnets each of y nodes can share
the one class B address
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Feb.2001
(instead of using x class B addresses.)
C.Watters
Subnet Network IDs
Subnet has its own network ID
This ID is a subset of the original classbased network ID
a 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
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Feb.2001
139.12.1.0
139.12.2.0
139.12.3.0
C.Watters
So what are subnet masks??
Subnet mask is used so that the local router
can extract the subnetted network ID
subnet mask

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

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 255.255.255.0
128 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 Addresses
source 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 hosts
Problem – 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
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Feb.2001
SO 220.78.168.0/21 is the CIDR block
C.Watters
4.Classless Domain routing
Addresses are prefix-free
initial 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 example
Still can have domains
194.23.17.4
Let 1st 3 bits designate continent
next 7 bits country
France may use 5 bits for town
Belgium may use only 4 bits for town
using 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 way
to 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 hosts
Millions of addresses are unused and
unusable!
Feb.2001
C.Watters
IPv6 Feature
128 bits address space
Advanced Routing Capability
Better Options Support
Better Quality of service Support
Authentication and Security
Feb.2001
C.Watters
A, B, C class of IPv4 address
Class prefix scope network ID host ID subnet mask
A
B
C
0
10
110
1-126 x.
128-191 x.x
192-223 x.x.x.
x.x.x
x.x
x
255.0.0.0
255.255.0.0
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 space
representation 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
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Feb.2001
prefix
reserved for IPX address
0000 010
reserved for NSAP address
0000 001
reserved for multicast address 1111 1111
unassigned address
101
……
……
C.Watters
IPv4 address transits to IPv6
IPv4-compatible IPv6 address
80 bits
16 bits
32 bits
0000…0000 0000
IPv4 address
Reference: RFC1881, RFC1887, RFC1924
Feb.2001
C.Watters
IPv6 Header is simpler:
Header of IPv6
Header of IPv4
Feb.2001
C.Watters
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.
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
Fields removed from IPv6
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.
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-out
Upgrade IPv4 router to IPv4/6 dual
router
Building up IPv6 only routing system

6-bone
Shutdown IPv4 in areas where there is
no need for IPv4
Feb.2001
C.Watters