Re: [SLUG] LAN config

From: Chris Mathey (slug@mathey.org)
Date: Wed May 31 2006 - 14:26:14 EDT


steve szmidt wrote:
> On Wednesday 31 May 2006 08:42, Chris Mathey wrote:
>
>>That's not exactly true. I have never seen a recent router with "hub"
>>ports. a hub is not full duplex, hubs are just repeaters, every host
>>connected see's every unicast and multicast. A switch know's every mac
>>address that is plugged into itself and only sends unicast frames to the
>>intended MAC address. Broadcast frames hit everything of course.
>
>
> Well this is not correct. A hub differs from a switch in that it will route
> traffic to all ports, much like a broadcast. While a switch will route it
> only to the correct port, where it's internal notes tracks what port each MAC
> (NIC) address uses.
>
> A hub is not a repeater, it's old technology from before switches were
> invented. Once switches showed up they solved the problems of collisions that
> the original hubs had.
>
> An Ethernet network was designed to have collisions of packets, and could in
> real life sustain about 30% of the traffic being collisions. Passing 30% it
> degraded rapidly.
>
> The switch solved the problem neatly and has but all replaced the use of hubs.
>

A hub is in other terms a "repeater" because when an ethernet frame
enters one of its ports it "repeats" that frame to all other ports. It
also amplifies the signal. In this environment (collision domain) the
protocol CSMA/CD to detect collisions.

Also a hub can only provide half duplex communication because a hub
takes the signal from the active incoming port and immediately pushes
the signal out on all outgoing ports at the same time after signal
amplification. Because this is going on at the same time, a hub needs to
do it in half duplex fashion.

Basically my statement was that if you go buy a router from compusa
netgear\dlink\linksys\et al they are switches and not hubs. The
internal software creates a separate VLAN for the WAN port and routes
between them.

Chris

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