----- Original Message -----
From: "Howard C. Berkowitz" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, January 23, 2001 9:02 PM
Subject: RE: But isn't that the routers job???
> >Plus routing of packets is done more quickly when done at the Switch
level
> >rather than having to go through the router for every packet.
>
> What's wrong with "going through the router," and how does routing
> through a switch differ from routing through a router?
<snip>
> Making forwarding decisions on layer 3 information is routing. Period.
I actually have to disagree here with your terminology I guess. Forwarding
decisions are being made with Layer 3 information. The first time a packet
hits that router, a decision is made as far as which exit interface the
packet should be sent to and the best route for the packet to hit its
destination, based on whatever policy/protocol the router is using to make
that decision in the first place. It is only subsequent packets that are
heading to the same destination that are spared the whole lookup process
again. Maybe my last email didn't send properly, but I replied to this one
last night that bypassing the RP is akin to an arp cache. Without an arp
cache, your device would overload looking up mac addresses. While your
router may not actually be crippled without this feature, and anyone that
has worked with enough 7500s knows that VIP cards are not the most stable
animals out there, it is a great feature if reduced latency is more
important to you than money, which is a point you made earlier.
> There are more and less hardware intensive ways to make routing
> decisions. But the actual lookup time is rarely a limiting factor.
I would have to disagree here as well. Perhaps lookup time isn't so bad if a
router is sitting on a T1 somewhere, but when you have multiple oc48s tied
into your router, processing time adds up, *real* quick.
Guy Tal
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