Date: Fri, 26 Mar 1999 17:39:54 -0700 From: Wes Peters <wes@softweyr.com> To: Mike Jenkins <mjenkins@carp.gbr.epa.gov> Cc: mm@i.cz, freebsd-net@FreeBSD.ORG Subject: Re: switch vs bridge (fwd) Message-ID: <36FC28DA.73DC2E28@softweyr.com> References: <199903262137.PAA06872@carp.gbr.epa.gov>
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Mike Jenkins wrote:
>
> On Fri, 26 Mar 1999 Martin Machacek wrote:
> > Layer 4 switch is a pure marketing bullshit.
>
> If I understand layer 4 switches correctly, they switch
> at the tcp/udp port number layer.
To a limited extent, yes. Most "layer 4 switches" implement a very
limited version of this.
> I could therefore slip
> a layer 4 switch between my router and my lan, and program
If you have a layer 3 switch, you don't need a router. Just put a
wide-area "blade" in the switch and route there. *Good* switches
router much faster than routers anyhow. I can't tell you how much
faster right now, or I'd have to kill you, but it's MUCH faster. ;^)
> it to redirect all incoming 25/tcp smtp connections to a
> mail filter host.
I supposed you could do that. It's usually used the other way around, to
try to provide a crude form of load balancing across mutiple http (i.e.)
servers. This turns out to be about as effective as round-robin DNS; a true
load balancer would be much more effective.
> I find that rather useful. I'm sure
> some folks use them for 80/tcp http redirection for web
> caching.
Well, more likely for bandwidth/performance management and hot failover.
> Aren't these useful applicatons?
Yes, but the actual features of most of these so-called "layer 4 switches"
is so minimal that you'll outgrow them almost immediately, at which time
you'd be better off with a REAL load balancer and a less expensive but
faster layer 3 switch.
> I realize routers can be programmed to do this but who wants
> to load down (or misconfigure) the router for this chore.
The switch *is* the router, unless you've just got balls of money you're
aching to get rid of. If so, call me. We can work together on this. ;^)
> A dual-homed unix box such as FreeBSD can also do this using
> redirection in packet filtering but that usually requires
> splitting the network into 2 IP networks (yes i've heard
> of dummynet/bridge but that is work in progress). I think
> a network appliance like a layer 4 switch would be the right
> tool for the job.
The you either don't understand the job, or don't understand the (very
limited) capabilities of these so-called layer 4 switches. It's not that
it's a bad idea, just that there are a couple of vendors out there giving
the idea a bad name with their implementations.
--
Where am I, and what am I doing in this handbasket?
Wes Peters +1.801.915.2061
Softweyr LLC wes@softweyr.com
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