Berkeley CSUA MOTD:Entry 39329
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2019/11/16 [General] UID:1000 Activity:popular
11/16   

2005/8/29-30 [Computer/Networking] UID:39329 Activity:moderate 54%like:37400
8/29    What's the difference between a hub, a switch and a router?  Thx.
        \_ AFAIK, probably be corrected by someone:
           hub: Allows communication on a LAN with bandwith shared amongs all
                the nodes on the hub and maxing out at the max line speed.
           switch: Allows communication on a LAN with bandwith greater than
                the max line speed (point to point)
           router: Allows communication between 2 different networks
           \_ The original difference between a hub and a switch is that
              a hub was multicasting whereas a "switch" (originally called
               a "switching hub") had enough circuitry to route signals
               to the appropriate port and that port only in which the
               destination IP was located. Obviously a multicasting
               hub would slow down the whole network with unnecessary
               chatter. A "router" used to mean devices which would
               route traffice between different LANs, although these days
               the terms have devolved so that they are somewhat
               interchangeable (all hubs have essentially become switches,
               it's actually somewhat difficult to find a hub these days, and
               many switches have essentially become routers).
           \- in practice these are used some what randomly right now.
              like managed switches are actually pretty smart. but sort
              of at a functional level: hub turns one network drop into a
              place you can plug in multiple devices. switch: sort of a
              set of point to point links making up a subnet based on
              arp/mac, and a router is what knows about "routing", i.e.
              IP addresses.
           \_ Hub: a multiport repeater, extends an ethernet "wire" to
                   multiple machines.
              Switch: a multiport bridge, separates ethernet collision
                   domains
              Router: communication interface between different IP broadcast
                   domains
              Layer 3 switch:  Basically a router with a built-in switch. -John
              \_ I see.  Currently I have Yahoo DSL and one PC at home.  The PC
                 connects to the only ethernet port on the DSL modem.  If I
                 want to add a second PC, I should buy a hub, connect the hub
                 to the DSL modem, and connect both PCs to the hub.  Is that
                 correct?  Thx.  -- OP
                 \_ Not exactly. The hub is not smart enough to translate
                    between the DSL modem and your PCs, and your modem will
                    balk at two PCs trying to talk to it at the same time.
                    Get a four-port router, place that between the modem
                    your PCs, and configure your router to make the connection
                    (i.e., get the IP address and serve DHCP to your PCs).
                    \_ What?  What DSL modem doesn't also function as a mini-
                       router?  The DSL modem port isn't magic.  It is pumping
                       out bog standard ethernet packets.  --boggle!
                       \_ Yahoo! SBC DSL is PPPoE. The router needs to
                          make the connection. The person above is
                          correct. Get a hub and place it between the
                          router and the modem. I guess this guy needs a
                          router, too. It's not the only way, but it's the
                          best and easiest way. In fact, many DSL routers
                          are also hubs so he only needs to buy one piece
                          of equipment.
                          \_ You failed to recognize DRIPPING sarcasm.  Your
                             penance is to watch George Carlin until your
                             brain melts
        \_ Nice nuke.  Hub = multiport repeater, extension of one ethernet
           collision domain to many wires/hosts.  Switch = multiport bridge,
           separates ethernet collision domains (when you hear that ethernet
           is contention-based, it means you have traffic from more hosts
           colliding on one "wire", slowing shit down.)  Router = separates
              \- this is getting less true *in practice* with gigE. it makes
                 life a lot more complicated to run half-dup and is largely
                 file a more more complicated to run half-dup and is largely
                 req'ed because of IEEE politics. do you know anybody running
                 1/2 dup gigE? see e.g. wl.20050819. do you think the person
                 asking the question know what things like "bcast domains"
                 mean?
                 \_ He asked for definitions.  The above are correct, _and_
                    try to answer his question (note: "try").  I don't
                    know anyone running gigE half duplex; I also don't know
                    anyone running gigE off a DSL line.  Hence: chill.  -John
                 \- BTW, in general there are a lot of weird performance
                    hacks in these networking devices so often they dont
                    operate the way you think they might. like some switches
                    start forwarding a packet before it arrives completely ...
                    it starts parsing the "front edge" header info ... so in
                    some cases part of the packet is already "in flight"
                    to the destination before the box "relizes" the checksum
                    has failed. anyway, this makes for all kind of weird
                    unintuitive behaviors, like why on some cases switching
                    between 10 and 100mbit can be slower than 10-10. etc.
                    a classic early example of this were the attacks on
                    cheep switches to get them to go into "repeat" mode
                    so you could sniff some extra traffic in a "switched"
                    environment. and mcast makes things a lot more complicated.
           IP broadcast domains and communicates transparently between them.
           A layer 3 switch is basically a router with a built-in switch, and
           a firewall is basically a bridge/switch or router with filtering
           logic.  In response to your question above, a hub will do fine.  I
           have no idea what the responder was on about with your DSL router
           (it's a router, not a modem, dammit) getting confused.  If you want
           higher speeds getting the PCs to talk to each other, get a switch,
           but you won't gain anything on your Internet connection.  Just make
           sure your DSL router (he's correct about the PPPoE, STFW) can
           accept connections from more than 1 client.  -John
           \_ The DSL modem and the DSL router are two separate devices.
              He said he has a modem. He never said if he has a router
              or not.
              \_ Rereading I guess you are objecting to the 'DSL modem'
                 terminology and realize this. He can do PPPoE from two
                 computers, but it would be easier to buy a router and
                 have it do the PPPoE instead of mere a hub.
              \_ Sorry, I have no idea whether I have a DSL modem or a DSL
                 router.  I signed up for the $19.95/mo plan in 3/05.  On my
                 SBC phone bill they charged me $99 and gave me a rebate for a
                 "DSL Modem Package".  So I always thought the black DSL thing
                 is a DSL modem.  I'll check the the labels on it and see if it
                 says anything.  -- OP
                 \_ OK, to be a bit less pedantic about it, generally, the way
                    DSL lines are implemented is by a device which has an
                    RJ11/45 port on one side doing "phone stuff" and RJ45
                    on the other side doing "ethernet stuff".  A "modem" is a
                    device which encodes digital signal in an analog sound
                    carrier.  Also, almost all DSL devices I have seen "route"
                    information between different IP subnets, hence the term
                    "router" (a router doesn't have to have ethernet on both
                    sides.)  This in almost no way affects your situation, just
                    trying to be informative.  I'm just a bit anal about
                    terminology.  -John
              \_ from a technical standpoint, most people use DSL routers and
                 know one class of routers as modems.  a true DSL modem would
                 provide what is essentially a serial bit stream interface,
                 or possible multiple streams with ASIC demultiplexors.
2019/11/16 [General] UID:1000 Activity:popular
11/16   

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