Link Layer Addressing - PowerPoint PPT Presentation

Loading...

PPT – Link Layer Addressing PowerPoint presentation | free to download - id: 20a2c0-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Link Layer Addressing

Description:

Email: carey_at_cpsc.ucalgary.ca. Class Location: ICT 122 ... In ARP table at source, find MAC address E6-E9-00-17-BB-4B, etc. A. R. B. CPSC 441: Link Layer ... – PowerPoint PPT presentation

Number of Views:21
Avg rating:3.0/5.0
Slides: 14
Provided by: anirban
Learn more at: http://pages.cpsc.ucalgary.ca
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Link Layer Addressing


1
Link Layer Addressing
  • Instructor Carey Williamson
  • Office ICT 740
  • Email carey_at_cpsc.ucalgary.ca
  • Class Location ICT 122
  • Lectures MWF 1200 1250
  • Notes derived from Computer Networking A Top
    Down Approach, by Jim Kurose and Keith Ross,
    Addison-Wesley.
  • Slides are adapted from the books companion Web
    site, with changes by Anirban Mahanti and Carey
    Williamson.

2
Link Layer Introduction
  • Some terminology
  • hosts and routers are nodes
  • communication channels that connect adjacent
    nodes along communication path are links
  • wired links
  • wireless links
  • LANs
  • layer-2 packet is a frame, encapsulates datagram

data-link layer (DLL) has responsibility of
transferring datagram from one node to adjacent
node over a link
3
Link layer context
  • Datagram transferred by different link protocols
    over different links
  • e.g., Ethernet on first link, Frame Relay on
    intermediate links, 802.11 wireless on last link
  • Each DLL protocol provides different services
  • e.g., may or may not provide reliable data
    transfer over link

4
Link Layer Services
  • Framing, link access
  • encapsulate datagram into frame, adding header,
    trailer
  • channel access if shared medium
  • MAC addresses used in frame headers to identify
    source, dest
  • different from IP address!
  • Reliable delivery between adjacent nodes
  • we learned how to do this already (chapter 3)!
  • seldom used on low bit error link (fiber, some
    twisted pair)
  • wireless links high error rates
  • Q why both link-level and end-end reliability?

5
Link Layer Services (more)
  • Flow Control
  • regulate transmissions between sender and
    receiver
  • Error Detection
  • errors caused by signal attenuation, noise.
  • receiver detects presence of errors
  • signals sender for retransmission or drops frame
  • Error Correction
  • receiver identifies and corrects bit error(s)
    without resorting to retransmission
  • Half-duplex and full-duplex
  • with half duplex, nodes at both ends of link can
    transmit, but not at same time

6
Adaptors Communicating
datagram
rcving node
link layer protocol
sending node
adapter
adapter
  • receiving side
  • looks for errors, rdt, flow control, etc
  • extracts datagram, passes to rcving node
  • adapter is semi-autonomous
  • link physical layers
  • link layer implemented in adaptor (aka NIC)
  • Ethernet card, PCMCI card, 802.11 card
  • sending side
  • encapsulates datagram in a frame
  • adds error checking bits, rdt, flow control, etc.

7
MAC Addresses (1/3)
  • 32-bit IP address
  • network-layer address
  • used to get datagram to destination IP subnet
  • MAC address (e.g., Ethernet LAN)
  • used to get datagram from one interface to
    another physically-connected interface (on the
    same network)
  • 48-bit MAC address (for most LANs) burned in the
    adapter ROM (globally unique)

8
MAC Addresses(2/3)
Each adapter on LAN has unique LAN address
Broadcast address FF-FF-FF-FF-FF-FF
adapter
9
LAN Address (3/3)
  • MAC address allocation administered by IEEE
  • manufacturer buys portion of MAC address space
  • MAC flat address provides portability
  • can move LAN card from one LAN to another
  • different than with IP addresses!

10
ARP Address Resolution Protocol
  • Each IP node (Host, Router) on LAN has ARP table
  • ARP Table IP/MAC address mappings for some LAN
    nodes
  • lt IP address MAC address TTLgt
  • TTL (Time To Live) time after which address
    mapping will be forgotten (typically 20 min)

237.196.7.78
1A-2F-BB-76-09-AD
237.196.7.23
237.196.7.14
LAN
71-65-F7-2B-08-53
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
237.196.7.88
11
ARP protocol Same LAN (network)
  • A wants to send datagram to B, and Bs MAC
    address not in As ARP table.
  • A broadcasts ARP query packet, containing B's IP
    address
  • Dest MAC address FF-FF-FF-FF-FF-FF
  • all machines on LAN receive ARP query
  • B receives ARP packet, replies to A with its
    (B's) MAC address
  • frame sent to As MAC address (unicast)
  • A caches (saves) IP-to-MAC address pair in its
    ARP table until information becomes old (times
    out)
  • ARP is a soft state protocol information that
    times out unless refreshed
  • ARP is plug-and-play
  • nodes create their ARP tables without
    intervention from net administrator

12
Routing to another LAN
  • send datagram from A to B via R
  • assume A knows B IP address
  • Two ARP tables in router R, one for each IP
    network (LAN)
  • In routing table at source Host, find router
    111.111.111.110
  • In ARP table at source, find MAC address
    E6-E9-00-17-BB-4B, etc

A
R
B
13
  • A creates IP datagram with source A, destination
    B
  • A uses ARP to get Rs MAC address for
    111.111.111.110
  • A creates link-layer frame with R's MAC address
    as dest, frame contains A-to-B IP datagram
  • As adapter sends frame
  • Rs adapter receives frame
  • R removes IP datagram from Ethernet frame, sees
    its destined to B
  • R uses ARP to get Bs MAC address
  • R creates frame containing A-to-B IP datagram
    sends to B

A
R
B
About PowerShow.com