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LAN Addressing. Network Protocols and Standards Autumn 2004-2005. An Internet Connection. End stations are connected to LANs LANs are connected through Bridges to form extended LANs Extended LANs are connected through gateways/routers/switches Layered architecture

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lan addressing

LAN Addressing

Network Protocols and Standards

Autumn 2004-2005

CS573: Network Protocols and Standards

an internet connection
An Internet Connection
  • End stations are connected to LANs
  • LANs are connected through Bridges to form extended LANs
  • Extended LANs are connected through gateways/routers/switches
  • Layered architecture
    • Connection is between “peers”
  • Service Models (Fig. 1.3 of Perlman)
    • PDUs (between peers) and SDUs(from up layers)

CS573: Network Protocols and Standards

local area networks
Local Area Networks
  • First part of the course
  • IEEE 802 Committee
    • LAN Standardization
    • Physical and Data Link Layers of OSI Model
    • Data Link layer subdivided by them:
      • MAC (Dependent on the type of LAN)
      • LLC (allows sharing data link resources)
    • Several LANs were standardized

CS573: Network Protocols and Standards

ieee 802 subcommittees
IEEE 802 Subcommittees
  • 802.1 --- common issues
  • 802.2 --- LLC
    • Does not deal with PHY and MAC
  • 802.3 --- CSMA/CD
  • 802.4 --- Token Bus
  • 802.5 --- Token Ring

LLC

Type 1, 2, …

Data Link

MAC

PHY

CS573: Network Protocols and Standards

lan addresses
LAN Addresses
  • Most LANs are “broadcast” type
  • LAN addresses solve two problems on shared (or broadcast) LANs
    • Who is the sender?
    • Who is the receiver?
  • IEEE 802 standardized the address length
  • Two different lengths were chosen
    • 16 bit (unique on the network) --- obsolete
    • 48 bit (unique globally --- plug and play)

CS573: Network Protocols and Standards

48 bit lan addresses
48 bit LAN Addresses
  • Globally unique
  • Assigned by IEEE
  • Cost is $1250 for a “block” of addresses
    • A “block” includes 224 addresses

2nd octet

3rd octet

4th octet

5th octet

6th octet

1st octet

Vendor code (OUI)

Vendor-assigned values

CS573: Network Protocols and Standards

48 bit lan addresses1
48 bit LAN Addresses
  • OUI = Organizationally unique identifier
    • Fixed value assigned by IEEE
    • 224 different possibilities
      • Not all of them are used!!!
  • Vendor-assigned Values
    • A total of 224 unique addresses are available by purchasing one block
    • A block may be shared
    • A vendor can buy more blocks with different OUIs

CS573: Network Protocols and Standards

group individual bit in oui
Group/Individual bit in OUI
  • In fact, One block  225 addresses
    • 224 of the addresses are unicast
    • 224 of the addresses are multicast
    • G/I bit decides if the address is multicast
      • G/I = 0 means unicast or individual station
      • G/I = 1 means a (LAN) multicast address

10111101

G/I (group/individual) --- first bit on the wire

G/L (global/local)

CS573: Network Protocols and Standards

global local bit in oui
Global/Local bit in OUI
  • Another bit in the OUI is designated by the IEEE as G/L bit
  • IEEE sets G/L = 0 when giving out the blocks of addresses
  • Addresses with G/L = 1 can be used without paying IEEE but the network administrator is responsible to assign addresses such that there is no collision
  • This leaves with 222 unique OUIs

CS573: Network Protocols and Standards

why multicast addresses
Why multicast addresses?
  • In most LANs (e.g., CSMA/CD LANs), every entity receives all the data on the LAN segment it is connected to
  • Hardware filtering is desirable because promiscuous listening is expensive
  • Some entities (e.g., bridges and LAN monitors) have to listen promiscuously

CS573: Network Protocols and Standards

protocol type multiplexing
Protocol Type Multiplexing
  • One station, many higher layer protocols
    • Which protocol is the desired recipient?
    • Which protocol constructed the packet?
  • This information is also included in the LAN header --- just like LAN addresses are!

IP

IPX

ARP

XNS

MAC Layer

CS573: Network Protocols and Standards

protocol type multiplexing1
Protocol Type Multiplexing
  • Original Ethernet design
    • 2 octet long field included in LAN header
    • Previously administered by Xerox, currently by IEEE
    • Protocol vendors need to negotiate for getting a protocol type added
    • http://standards.ieee.org/regauth/ethertype/index.html

6 octets

2 octets

variable

6 octets

Destination

Address

Source

Address

Protocol

Type

Data

CS573: Network Protocols and Standards

sap multiplexing
SAP Multiplexing
  • More flexible to have separate source and destination protocol type fields
    • Can assign different numbers to the same protocol on different machines
  • Service Access Points (SAPs)
    • Included in 802 LAN header
    • SSAP and DSAP
      • 1 octet each but only 6 bits are used

CS573: Network Protocols and Standards

sap multiplexing1
SAP Multiplexing
  • All 1’s  ALL SAPs
  • All 0’s (except G/L)  data link layer itself
  • 6-bit globally assigned SAP numbers (by IEEE)

6 octets

2 octets

2 octets

variable

6 octets

length

DSAP SSAP

Destination

Address

Source

Address

Protocol

Type

Data

10111101

G/I (group/individual)

G/L (global/local)

CS573: Network Protocols and Standards

sap multiplexing2
SAP Multiplexing
  • G/L bit is similar to the one used in LAN addresses
  • G/I bit --- perhaps to keep compatibility with the LAN addresses???
    • G/I bit in LAN addresses was used to make hardware filtering convenient
    • Hardware filtering is meaningless in SAP multiplexing
  • Only 64 unique SAP protocols are supported
    • Strict rules for assigning a SAP number
    • Protocol must be designed by standard bodies

CS573: Network Protocols and Standards

sap multiplexing3
SAP Multiplexing
  • Local SAP protocols can be used
    • Network/Protocol manager’s responsibility to ensure unique SAPs to protocols
    • Conversation startup is difficult

CS573: Network Protocols and Standards

snap sap
SNAP SAP
  • Subnetwork Access Protocol
    • Single globally assigned SAP value
    • AA hex (10101010) --- SNAP SAP
  • When DSAP = SSAP = SNAP SAP
    • Header is expanded to include a “protocol type” field
  • A “longer” protocol type field can then be used
    • Standardized to 5 octets

CS573: Network Protocols and Standards

addresses and protocol types
Addresses and Protocol Types
  • By using 5 octets to indicate protocol type, LAN address administration is tied to protocol type administration

2nd octet

3rd octet

4th octet

5th octet

6th octet

1st octet

LAN

Addresses

Vendor code (IEEE-assigned)

Vendor-assigned values

Protocol

Type

2nd octet

3rd octet

4th octet

5th octet

1st octet

CS573: Network Protocols and Standards

transmission bit order
Transmission Bit Order
  • 802.1 defines a canonical format for LAN addresses
    • 00-60-1D-23-20-A9
  • 802.3 and 802.4
    • LSB is transmitted first
  • 802.5 and FDDI
    • MSB is transmitted first
  • Internetworking different topologies
    • Bit order should be shuffled if forwarding frames between incompatible LAN topologies

CS573: Network Protocols and Standards

frame formats
Frame Formats
  • Ethernet
  • 802.3 Frame Format
  • Formats are compatible (Max length: 1536)
    • Protocols are assigned values > 0600 hex (=1536)

6 octets

2 octets

6 octets

Destination

Address

Source

Address

Protocol

Type

Data

6 octets

2 octets

2 octets

6 octets

length

DSAP SSAP

Destination

Address

Source

Address

Protocol

Type

Data

CS573: Network Protocols and Standards