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RE: What is the differents between Switch and Router?

2001-03-17 15:20:02
In telecommunications, a switch is a network device that selects
a path or circuit for sending a unit of data to its next destination.
A switch may also include the function of the router, a device or
program that can determine the route and specifically what adjacent
network point the data should be sent to. In general, a switch is
a simpler and faster mechanism than a router, which requires
knowledge about the network and how to determine the route.

Ref : http://whatis.techtarget.com/WhatIs_Definition_Page/0,4152,213079,00.html

Somehow, I find definitions from marketing outfits like techtarget.com
other than authoritative.  However an outfit "squarely focused on the
information technology space" might not be a marketing outfit.  I'm unable
to translate http://techtarget.com/html/about-ttc.htm into English.

That definition of of "switch" is a classic example of why it is best
to ignore marketing and sales people when they talk technical.  Usable
bridges have always needed know something about network topology, which
is why such protocols as Spanning Tree exist.  Besides, doesn't Spanning
Tree tell more about network topology than IP distance vector protocols,
for nearby connections if not distant networks?  A box running at wire
speed cannot be any faster, so are all modern routers "switches?"  Whether
an IP router using RIP is more complicated than a bridge using Spanning
Tree is not clear to me.  A "switch" that does not "determine the
route and specifically what adjacent network point the data should be
sent to" doesn't sound very useful.

Or maybe that definition of "switch" is a proof that "switch" in packet
contexts is content-free marketing blather or worse, nonsense intended to
bamboozle the suckers.



] From: Harald Alvestrand <Harald(_at_)Alvestrand(_dot_)no>

] ...
] That's my reason to use the TTL decrement; if someone shows me a device 
] where a packet comes in on one interface with a certain TTL, and it comes 
] out on another interface with a lower TTL but no other significant changes, 
] I call it a router.
]
] If it is incapable of not doing other significant damage, I call it an 
] application layer gateway, a NAT box, or something else, but not a router.

What about the changes to the IP header required to deal with an
IP record-route option?  There seem to be three types of routers:
 1. those that deal with LSRR and RR options correctly
 2. those that mess them up, including generating pure garbage IP packets
 3. those that ignore them.
As far as I can tell, Type 1 and Type 2 are each more common than Type 3.


Vernon Schryver    vjs(_at_)rhyolite(_dot_)com