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Internetworking

Internetworking

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Internetworking

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  1. Internetworking

  2. Module contents • Concepts • Bridges • Routers • Switches • Voice over Wireless (SpectraLink support)

  3. Application Application NOS NOS Presentation Presentation Session Session Transport Protocol stack Transport Protocol stack Network Network LLC LLC Network DRIVER NDIS NDIS Network DRIVER ORiNOCO PC Card ORiNOCO PC Card * * ConceptsOSI reference • 7 Layer model • Isolate protocols • Make higher layer protocols insensitive to lower layer issues • Allow different implementations of lower layers without effecting higher layers • ORiNOCO products operate on layer 1 and 2 • Physical Layer (I.e. the air) • Data Link Layer (I.e. MAC layer)

  4. Application Application NOS Presentation Presentation Session Session Transport Protocol stack transport Network network LLC Protocol LLC LLC NDIS MAC Bridge MAC y Physical y Physical y ORiNOCO PC Card ORiNOCO PC Card * * Concepts MAC Bridge • MAC Bridge • Defined in IEEE 802.3 • Operates on MAC addresses (Hardware addresses) • Independent of lower protocols • Connects physical interfaces • Wired to wired • Wired to wireless • Wireless to wireless • No intelligent routing capabilities; merely filter or forward • Does not operate on IP packets except for specific implementations: • SNMP traffic meant for the bridge itself • To allow filtering of special traffic (Voice packets), only in ORiNOCO AP-1000/AP-500

  5. Application Application Presentation Presentation Session Session Transport Protocol Transport transport Network network Router LLC LLC x Data Link y Data Link y ODI ODI Physical y Physical y ORiNOCO PC Card ORiNOCO PC Card * * Concepts Router • Router • Dedicated to a specific protocol • Knows to complete network and selects the best route • Operates on additional address information e.g. IP-router operates on IP addresses

  6. Application Gateway Application Presentation Presentation Presentation Presentation Session x Session x Session y Session y Transport x Transport x Transport y transport y Network x Network x Network y network y LLC x LLC x Data Link y Data Link y MAC x MAC x Physical x Physical x Physical y Physical y Concepts Gateway • Gateway • translates two “incompatible”protocols • dedicated to a specific Interface • Does not necessary have to be 7-layered protocols on either side of the gateway • e.g. IPX to SNA • Other example is the Spectralink PBX Gateway that connects IP traffic to a PBX (details later in this module)

  7. MAC Bridges • Operate on MAC address (Hardware address) • Unicast • Broadcast • Multi-cast • Use Dynamic and Static Filter Tables • Can use Access Control Filter Table • Filtering • Forwarding

  8. OUI Unit specific portion Example: 0 2 0 2 D 1 F 8 0 0 2 D Multi-cast bit ‘1’ - Multi-cast address ‘0’ - Uni-cast address Local Address bit ‘1’ - Local MAC address ‘0’ - Global MAC address BridgesMAC addresses andfilter tables • MAC addresses: • 6 octet unique hardware address assigned to network adapter • Global MAC address assigned in the factory and stored in Flash • Vendor specific part (1st 3 octets), also known as OUI (Organization Unique Identifier) • ORiNOCO hex ‘00 02 2D’ • Unit specific part (2nd 3 octets) • Local MAC address can be assigned by user • Broadcast MAC address used to address all stations on a sub-net (hex ‘ FF FF FF FF FF FF ‘) • Multi-cast MAC address used to address a specific group (protocol specific)

  9. BridgesMAC addresses andfilter tables • Contain MAC-addresses of wired-LAN and wireless stations • Used by bridge software to make decisions on filter or forward • Filters can be used to: • Improve performance • Improve security (access control)

  10. Wireless Wired LAN MAC address 08-00-0E-12-34-56 MAC address 0A-01-08-AB-CD-EF MAC address 08-00-0E-22-32-44 BridgesDynamic Filter Table • Table is dynamically created and maintained by the bridge • Also known as Bridge/Learn table • Records stations by source address • associates the station with the interface (port) it was received on • Table will be updated when address in the table appears to come in on a different interface than recorded in the table

  11. Wireless Wired LAN MAC address 09-FF-FF-FF-FF-FF BridgesStatic Filter Table • User Configured Filter Table • To be used to filter protocol specific multicast traffic from wired devices to ORiNOCO wireless cell. • Reduces wasting wireless bandwidth • Broadcast traffic can never be filtered

  12. Wireless Wired LAN MAC address 08-00-0E-12-34-56 MAC address 08-00-0E-22-32-44 BridgesAccess Control Filter Table • When enabled: AP-500 / AP-1000 will only forward frames if the MAC address of the wireless station (source address) is included in the Access Control table • broadcast and multicast messages not filtered out

  13. BridgesFiltering & Forwarding • check 1: (only when Access Control is enabled) • source address in Access Table ? • YES : continue with 2 • NO : drop message • check 2: Filter/Forward (uses Dynamic and Static Table) • destination address in tables? • YES at same port: drop message • YES at other port: forward • NO : forward

  14. 32 bits Network Host Network (21) Host (8) 1 1 0 Class C Class B 1 0 Network (14) Host (16) . . . Class A 0 Network (7) Host (24) 192 121 135 143 Decimal dotted notation IP Addresses RoutersInternet Protocol (IP) • Operate on IP addresses • Map IP addresses to hardware address (MAC address) • Use Routing tables to determine path • To allow IP sessions to be carried out, participating stations need to have a unique “IP-Address” • Manually set (e.g. specify in TCP/IP protocol stack properties) • Dynamically assigned by DHCP server

  15. RoutersHow DHCP Clients get IP addresses • When “leasing” IP addresses a DHCP Server must be present and “reachable” • Dynamic IP addresses are typically assigned for a duration (lease time) • Release and renew of IP address can be done manually or at start of day • Windows tools available: • IPCONFIG • WINIPCFG

  16. RoutersDHCP Clients & Servers on a Routed Network • Network can be divided in sub-nets: • Portion of the host address becomes the sub-net address • Sub-net mask identifies which portion of the address is the sub-net address • Routers separate IP networks and IP sub-nets.

  17. RoutersDHCP Clients & Servers on a Routed Network • IP communication between Stations: • Station matches the destination IP address with its own sub-net address ((logical AND with the sub-net mask) • When destination is on same sub-net, the sender consults a table in cache that maps IP address to MAC address; when MAC address is found the frame is send on the media • When no entry is found the station issues an ARP request (Address Resolution Protocol). This is a broadcast MAC frame containing the destination IP address in its payload • Another station that recognizes its IP address in payload will respond, and so pass it’s MAC address • When destination is not on the same sub-net the station will pass the frame to the default router for relay to another sub-net

  18. SwitchesBridges versus Hubs versus Switches • Bridge • Intelligent device that separates domains of MAC addresses • Uni-cast frames flow from one port to another, only when recipient resides on another port (determined by information in the bridge table) • Most often 2 ports (though AP-1000 is a 3-port bridge) • Hub • Devices that electrically connects stations (using wire) • Uni-cast frames flow to all other ports on the hub (no filtering) • Number of ports can vary and is always larger than four • Switches • Multi-port bridges (number of ports typically larger than 4) • Uni-cast frames are propagated to a single port based learn tables

  19. SwitchesSwitch operation • Act as bridge (in most cases), • learns changes in topology (Station is moved from one port to another, for instance in case of roaming)) • However….. • Some bridges may not operate as above and flag a the move as an address violation (duplicate MAC address) • Most bridges can be reconfigured to solve the above issue. • Switches that may give problems: • Cisco Catalyst Series (19xx / 29xx) • Switches that are known to allow roaming stations without problems: • Avaya Cajun M450 • 3Com Superstack Switch (11xx series) IAPP (WMP Announce protocol) is required to assure updating of the learn tables when a station roams

  20. Voice over wirelessSpectraLink Voice Priority • SpectraLink provides handsets with IEEE802.11 radio capability, to allow using the existing 802.11 infrastructure to carry voice traffic • System consists of: • Wireless Handsets • Telephone gateway reachable via Ethernet backbone and connecting to PBX • For effective use of this equipment voice priority has been implemented within the FW of the PC card in the AP

  21. Gateway AP Handset 802.3 802.11 SVP IP packet SVP IP packet IP Hdr Voice data IP Hdr Voice data 802.3 Frame 802.11 Frame IP Hdr Voice data IP Hdr Voice data Voice over wirelessSpectraLink Voice Priority • SVP is SpectraLink Proprietary protocol (using Isochronous packets): • End to end protocol between Gateway and Handset, where Spectralink packet is encapsulated in IP packet • Provision to avoid collisions • Provision to provide fairness between handsets • Control of number of handsets that access AP simultaneously

  22. Voice over wirelessSpectraLink Voice Priority Changes in the AP to support SVP: • Detection by bridge kernel of IP packets are meant for the handsets (identified by “protocol” field in the IP header) • Priority transmission by the AP Firmware in the PC Card of the frames meant for the handsets: • Queue the traffic in front of other frames • Use zero back-off timer • Transmit directly on DIFS

  23. Voice over wirelessSpectraLink Voice Priority Current limitations: • Frames are transmitted as multi-cast frames (no need for ACKs), but current Spectralink systems support 2 Mbps only; Hence multi-cast rate has to be set to 2 Mbps • No support for encryption; WEP should be disabled • For effective use the max number of active handsets per cell should not exceed 5

  24. Module summary • Concepts • Bridges • Routers • Switches • Voice over Wireless (SpectraLink support)

  25. Your Mobile Broadband Connection