Routing

Document Sample
Routing Powered By Docstoc
					                                  TCP/IP




Bridging, Switching and Routing
            in LANs
           Alvin Kwan
Bridge
         TCP/IP
          Segmenting with Bridges
                                                          TCP/IP



   A bridge is the middle device between
    network segments within a LAN
    • It aims to reduce data collisions by separating
        collision domains between segments
    •   It works on the data link layer with the use of
        the MAC address
    •   It has a buffer (memory) to keep MAC
        addresses of the network devices in each
        network segments through a self-configuring
        process
        How does Bridging work?
                                                   TCP/IP



   A bridge builds an address table that consists of
    an up-to-date listing of every MAC address on
    the LAN, as well as the physical bridge port
    connected to the segment containing that
    address by listening to all LAN traffic.
   When a frame is addressed to an unknown
    MAC address, the bridge will propagate that
    frame to all its attached LAN segments (except
    the segment from which the frame is received).
            Important Remarks
                                                     TCP/IP



   A bridge must adhere to the media access
    protocol, e.g. an Ethernet bridge must conform
    to the CSMA/CD media access protocol.
   No matter how many bridges are in a network,
    the entire network will share the same logical
    broadcast address space.
   Bridging may increase a latency 10%-30%.
                  Bridge Types
                                                             TCP/IP



   Some major bridge types are as follows:
    • Transparent bridges
        Link together segments of the same LAN type
    • Speed-buffering bridges
        Similar to transparent bridges except that linked
         LAN segments may be of different speeds
    • Translating bridges
        Similar to transparent bridges except that linked
         LAN segments may be of different LAN types
               Bridging Today
                                                  TCP/IP



   Most bridges are two-port device though multi-
    port bridges are available too.
   Bridges are becoming obsolete because their
    functions have been almost “subsumed” by
    other networking devices, noticeably LAN
    switches.
   Hubs with high performance up-link ports are in
    fact bridges in disguise.
                    Exercise
                                                      TCP/IP



   Connecting network devices arbitrarily to
    different network segments separated by a
    bridge will not be able to make the best use of
    a bridge. Why?
Switch
         TCP/IP
         Segmenting with Switches
                                                         TCP/IP



   A switch is the multiport data link layer device
    • It aims to reduce data collisions by associating
        each port with its own collision domain
    •   It uses the MAC address
    •   It dynamically builds and maintains a MAC
        filtering table, holding all of the necessary
        MAC information for each port
              Switching Issues
                                                     TCP/IP



   Address learning (when a switch is just turned
    on OR change in network configuration)
   Forward/filter decision
   Loop avoidance
Address Learning (1/3)
                         TCP/IP
Address Learning (2/3)
                         TCP/IP
Address Learning (3/3)
                         TCP/IP
       Forward/Filtering Decisions
                                                              TCP/IP



   When a frame arrives at a switch, the switch checks
    the destination hardware address, which is compared
    to the forward/filter MAC database. If the destination
    hardware address is known, then it will transmit it out
    the correct port, but if the destination hardware
    address is not known, then it will broadcast the frame
    out of all ports, except the one which it received it
    from. If a device (computer) answers to the
    broadcast, then the MAC address of that device is
    added to the MAC database of the switch.
              Loop Avoidance
                                               TCP/IP



   Any potential problem with the following
    network configuration?
          Store & Forward Mode
                                                           TCP/IP



   When the switch receives a frame from one of
    it's ports, it will store it in memory, check it for
    errors and corruption, and if it passes the test,
    it will forward the frame out the designated
    port, otherwise, if it discovers that the frame
    has errors or is corrupt, it will discard it.
   This method is the safest, but also has the
    highest latency.
             Cut-through Mode
                                                        TCP/IP



   The switch reads the frame until it learns the
    destination MAC address of the frame it's
    receiving. Once it learns it, it will forward the
    frame straight out the designated port without
    doing any error checking.
Memory Requirement for Switch
                                TCP/IP
Routing
          TCP/IP
                    Routing
                                                   TCP/IP



   Concerns with “learning how to get from here
    to there”
   Works on the network layer, i.e. Layer 3.
   Two major camps
    • Source routing (less common)
    • Hop-to-hop routing (predominately used in
      TCP/IP networks)
             Routing Principles
                                                TCP/IP



   Correct route
   Most direct route
    • Shortest route
    • Route takes the least time
   Most reliable route (which may not be the
    shortest one)
Routing Requirements over Internet
                                                   TCP/IP



   Static routing cannot help; good routing has
    to be
    •   dynamic
    •   adaptive
    •   decentralized
    •   scale well, and
    •   resilent
               Source Routing
                                                   TCP/IP



   Routing information is collected by the source
   Routing information is put into the packets that
    the source launches toward the destination
   Intervening network (with intermediate links
    and systems) read the routing information from
    the packets and act on it accordingly
   Example: route planning by most people is a
    kind of source routing
             Hop-by-hop Routing
                                                        TCP/IP



   Hop-by-hop routing requires
    • routing protocols that allow end systems and
        intermediate systems to collect and distribute the
        information necessary to determine routes
    •   a routing information base containing information
        from which routes between end systems can be
        computed, and
    •   a routing algorithm that uses the information
        contained in the routing information base to derive
        routes between end systems
Example: Hop-by-hop Routing
                              TCP/IP
       Example: Simple Routing
                                 TCP/IP



   Connected network
        Example: Simple Routing
                                                    TCP/IP



   Connected network (no routing is required)




   Q: What is the range of addresses that Node
    B can take such that it can “talk” to Node A?
         Example: Simple Routing
                                                        TCP/IP


   Unconnected network
    • As A and C are separately connected to
        different networks, they are unconnected.
    •   Without setting up routing, no communications
        can be achieved between A and C.
Example: Routing Table
                         TCP/IP
Example: Routing Table
                         TCP/IP
Example: Routing Table
                         TCP/IP
Example: Data Link Frame
                           TCP/IP
TCP/IP
                    Exercise
                                                   TCP/IP



   Suppose we would like to improve the
    effective bandwidth of a LAN with no subnet
    definition, would a switch be more favorable
    than a router? Why?
Fault Tolerance of Switch
                            TCP/IP
Fault Tolerance of Router (1/2)
                                  TCP/IP
Fault Tolerance of Router (2/2)
                                  TCP/IP
Broadcast Flood (1/2)
                        TCP/IP
Broadcast Flood (2/2)
                        TCP/IP
            Important Remarks
                                                    TCP/IP



   Switching builds logically fat networks
    whereas routing builds logically hierarchical
    networks
   Switches segment LANs whereas routers
    tend to segment WANs
   Exercise (source: http://www.mpi-
inf.mpg.de/~weidenb/Lan2004/exercise8.pdf)
                                             TCP/IP
                 References
                                                TCP/IP



   Wikipedia’s pages on network switch and router
   http://www.ripe.net/meetings/regional/dubai-
    2003/presentations/routing-smith.pdf
   http://www.soi.wide.ad.jp/soi-
    asia/pkg1/06/index_bar.html
   http://www.corecom.com/html/OSNconnexions.
    html

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:10
posted:2/15/2012
language:English
pages:43