feb.2001c.watters names and addresses what’s in a name, anyway? 1011010011001110000111001100110
TRANSCRIPT
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