Topics - Addressing

• CIDR

Addressing

• 32 characters, A-Z, 0-9, -, _

• Case insensitive

• For software: IP address

• 32 bits, dotted decimal representation

• For hardware: Link level address

• 48 bits, hexidecimal representation

• Ethernet’s first 24 bits identify manufacturer of interface card

• Last 24 bits a unique serial number

• FDDI addresses are 48 bits too

IP Address Details

• 128.138.243.151

• Identifies a "computer’s" network in-terface

• "computer" can be

• normal computer

• network device

• printer

• toaster (soon)

IP Address, cont.

• Ethernet interface, cost $50-100

• FDDI interface, cost $2000-4000

• Serial port for SLIP/PPP, cost $8

• ATM interface, cost$500-1000

• WAN connection

• T1 (1.5mb/sec), cost $1500-3000

• T3 (45mb/sec), cost $20,000

Address Classes

• Made separating the network part and host part easier

• Inefficient use of address space

• Designed when "The network (ARPANet at the time) might grow to 200 hosts maximum"

Class A Network: N.H.H.H

• First byte 1-127, first bits 01

• Only 127 networks, but 2**24 hosts

• Huge network, too big

• Subnetted to N.S.S.H usually

Class B - N.N.H.H

• 63*255 networks, 2**16 hosts

• Size about right for medium to large or-ganization

• Usually subnetted to N.N.S.H

Class C - N.N.N.H

• 32*255*255 networks

• But only 255 hosts each

• Size too little for most organizations

• Used to be no way to subnet

Other Classes

• First byte 224-239, first bits 1110

• Used for multicast

• Class E

• First byte 240-254, first bits 11110

• Used for experiments

Address Depletion

• Running out of addresses

• Out of class B’s by mid ’95

• Routing tables too large

• Each class B is 1 routing table en-try (OK)

• Each class C is 1 routing table en-try (Not OK)

• Network growing exponentially

Address Depletion

• Long term fix: Bigger IP addresses, new IP protocol

• Called IPv6

• 128 bit addresses

• Last protocol change:

• Occurred in 1978-81 NCP (Network Control Protocol) to TCP/IP

• Took 3-4 years to complete the change

• The network was infinitely smaller then

CIDR

• Use netmask variable and notation /xx for xx bits of network address

• Traditionally:

• Class A network is /8

• Class B is /16

• Class Cis /24

• Under CIDR /xx is OK for almost any xx

Implications of CIDR

• Had to change to use netmask

• Routing protocols had to include net-mask

• People had to learn binary/hex better

• More efficient allocation of addresses fixes depletion, what about routing table explosion

CIDR Blocks

• CIDR says no:

• You can have 64

• You can have 128

• But not 100, say you take 64 = 2**6

• Creates block of addresses with

< - - - - - - - > | < - - - - - - - - > < - - - >

constant 6 bits host

CIDR Block, cont.

• But, don’t need 64 routing table entries

• Just list routing info as one entry with netmask 6 bits less.

<- - - - - - -> <- - - - - ->

constant 6 bits

bits in CIDR block

<- - - - - - - - - - - - - - - - ->

customer network length

<- - - - - - - - - ->

routing network length

CIDR Example

1 9 2 . 1 3 5 . 0 . H

1 9 2 . 1 3 5 . 1 . H

1 9 2 . 1 3 5 . 2 . H

1 9 2 . 1 3 5 . 6 3 . H

as 192.135.0.0./18 and use the netmask

255.255.192.0

• Arithmetic gets messier if not on byte boundary and not starting with 0

Special IP addresses

• 127.0.0.1 local host, loopback address

• 127.x.x.x. still local host

• host bits all =0 network address

• host bits all =1 broadcast address

Special Addresses Example

• 192.135.1.0.0/18 is net address exter-nally

• 192.135.1.0/24 is an internal class C

• 192.135.2.0/26 is an internal class C di-vided into 4 pieces (first piece)

• 192.135.2.64/26 is the second piece

• 192.135.2.127is the broadcast address of the second piece

Today’s IP Addresses

• Class A- rarely allocated

• Class B- very tight, trying to reclaim under-utilized ones

• Class C

• Old ones allocated called the

• 192-swamp

• New ones allocated in CIDR blocks

• Everyone getting good at netmasks

• Everyone getting stingy at giving them out in large blocks

IP Allocation

• Now in US

• NIC replaced by ARIN who sells to ISPs

• ISPs sell/give to customers

• Sometimes many levels, not just 2 shown

• In Europe - RIPE, in Asia - APNIC

• Who owns address

• ISP

• Customer

• How can customer change ISPs --renumber?

IP Allocation, cont.

• Took SGI 2 years, several staff

• ISPs mostly say they won’t "give" ad-dresses

• Address stays with ISP

• IETF came up with "fix"

• Identified range of numbers for inter-nal use, called private networks

• Not routable

• Not unique

• Proxy machine converts to real #’s

• Called NAT - Network Address Trans-lation