Network Devices CPSC 330 - Fall 2002 devices typically categorized according to layer +-----------+ |application| http / domain name -- gateway (may be software on host) +-----------+ ... +-----------+ | transport | tcp / port -- gateway (may be software on host) +-----------+ | network | IP / IP address -- router, switch +-----------+ | data link | Eth. / MAC address -- network interface card, bridge, switch +-----------+ | physical | bits -- repeater, hub, switch +-----------+ NIC - network interface card (adapter), plugs into computer and attaches computer to the network repeater - works at physical level, extends bus-like LAN segment (strengthens signals for increased distance), limit to number of nodes supported (http://www.netbook.cs.purdue.edu/figures/f11_3.htm) (repeater-connected stations are in the same collision domain for Ethernet networks) hub - works at physical level, central connection in star topology, all connected nodes are in the same LAN segment, more sophisticated hubs can disconnect failed nodes and monitor traffic (http://www.netbook.cs.purdue.edu/figures/f8_3.htm) (hub-connected stations are in the same collision domain for Ethernet networks) bridge - works at data link level with physical (MAC) addresses, connects LAN segments into a single IP subnet, typically plug and play connection type local - one bridge physically attached to multiple LANs (http://www.netbook.cs.purdue.edu/figures/f11_6.htm) remote - one bridge per LAN communicating over subnet (http://www.netbook.cs.purdue.edu/figures/f11_7.htm) protocol conversion transparent - similar LANs (have same data-link protocols) translation - dissimilar LANs often self-learning (or adaptive) with regards to traffic and provides traffic isolation (i.e., separate collision domains) 1) observe source MAC addresses of frames as they pass across the bridge and collect entries into a table 2) if a destination MAC address matches a table entry, use the port value in that entry to determine if the frame should be sent to another LAN or if the frame destination address is on the same LAN (i.e., the same port) as the source address (in which case the frame is not sent across the bridge) 3) if a destination address doesn't match a table entry, broadcast the frame (i.e., flood the frame across the attached LANs) if LAN segments are interconnected in such a way that a loop exists, then spanning tree decisions must be made so that some bridges will not forward traffic router - works at network level with IP addresses, filters and routes IP packets, uses cost metrics in a routing table to determine the best path, separates each connected LAN into separate IP subnets, typically must be configured gateway - works at transport level or above, converts protocols, may be a combination of hardware and software (e.g., software on host) switch - generic term - different types work at data link to network levels, more recent in design than hubs or bridges, more efficient, typically has a larger number of ports (input and output lines) than available on a hub or bridge, aimed at displacing hubs and bridges (some switches even perform router-like functions), typically must be configured, ports can be arranged into logical groups called VLANs +----------+ input line ->| switch |-> output line input line ->| fabric |-> output line ... ->| |-> ... +----------+ switch fabric can be a single bus, a crossbar switch, or a memory store-and-forward - switch buffers the complete frame before forwarding cut-through - transmission starts as soon as destination address has been read functional comparison hubs bridges routers switches traffic isolation no yes yes yes plug and play yes yes no yes optimal routing no no yes no cut-through yes no no yes note: some sources now use the term "bridge" to mean a switch with multiple stations attached to each port versus "switch" to mean one station per port -------------------------- [extra info, not required] devices are also categorized according to position in network access/gateway LAN switching Ethernet FDDI wireless LAN bridges 802.11 edge termination access concentrators DSLAM VLAN gateways telephony VoIP VoATM modems xDSL ISDN analog cable edge/server firewalls and VPNs VPN switch NAT router WAN bridge IP over ATM L3+ network/storage caching SSL acceleration WAN packet switching ATM frame relay IPv4 WAN circuit switching xDSL ISDN core backbone routers IP ATM frame relay optical cross connections SONET ATM over WDM