Sabrina Kilian a écrit :
> Francois Labreque wrote:
>> Sabrina Kilian a écrit :
>>> It is an interesting way to use commodity hardware, instead of custom
>>> stuff. Though, the article does make it hard to take them seriously when
>>> they use lines like "Modern routers are rarely dumb switches anymore."
>> Most comemrcial routers HAVE been switches for the last 20 years.  The
>> first packet to come through would be routed by the cpu, but the result
>> of that routing table look up would be sent to an interface cache and
>> all the packets for the same destination after that would be switched
>> directly by the interface hardware, leaving the CPU alone.
> 
> Switches have moved up to handling some of the layer 3 protocols and
> doing some of the stuff typically thought of as router work. Managing
> VLANs and the like, and switching stuff between them. If the router
> never had to handle BGP, and the like, then a smart switch could replace
> it. Depending on the switch, it might even work where all you need is
> QoS and some switching between local disparate IP subnet and VLAN.
> However, a smart switch won't replace a router where one is really
> needed; handling all the annoying route finding when you have a more
> complex topology outside the area of your network. At least, I haven't
> seen one that manages BGP. Wiki tells me they may exist.
> 

Even if it does appear that the author of the article's experience with 
routers is limited to the Linksys or Netgear home stuff, I'm not talking 
about "layer-3" switches.  I'm talking about a router that does 
switching in hardware based on mac-addresses.

> Still, all of this is smart switches moving up to fill the need of
> simpler routers. Any router, barring marketing names, has never just
> switched packets on layer 2 like a dumb switch will.
> 

The Cisco 7000 or 7500 series have been doing just that, and the newer 
GSR and CRS models do it as well.  As I said earlier, the first packet 
to come by will be CPU-routed, but all the following ones* for that same 
destination will be handled in hardware based on mac-address look-ups. 
This is how a Cisco 7000 was able to handle 16M pps with only a 33Mhz 
CPU, 20 years ago.

-- 
/*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
/*    flabreque    */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
/*        @        */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
/*   gmail.com     */}camera{orthographic location<6,1.25,-6>look_at a }

Post a reply to this message