On Thu, 19 Aug 1999, Jeff Mcadams wrote:
> Thus spake Alan Cox
> >> - memory copies. As I understand it, to switch a packet through a Linux
> >> router, there are at least 2 memory copies....the packet is received and
> >> stored in the nic buffer...from there it's copied into main memory...I'm
> >> assuming the Linux kernel is very efficient and doesn't do any copies of
> >> its own...from there its copied into the outgoing nic's packet buffer.
>
> >Most NIC's have only FIFO's . Main memory is their ram buffer. One card DMA's
> >it in, the other DMA's it back out when using the fastroute aware tulip
> >driver.
>
> OK...even at that though...you're dealing with two DMA's across a PCI
> bus compared to what's essentially a single DMA across a much higher bus
> speed in most Cisco's.
I will have to check the references but Alexey and somebody else had
posted hard numbers as versus a 3xxx Cisco platform and fastroute kept up.
[snip]
> >> - extensive switching support. To my understanding, you can't have a
> >> linux box with 4 ethernet cards and bridge between eth0 and eth1, and
> >> then bridge between eth2, and eth3, and then route between the eth0/1
> >> combo and the eth2/3 combo. IOS handles that with no problem. Other
>
> >Correct. We don't support fancy switching. Linux is a router it doesnt really
> >have any pretense at switching. Measure the latency on a really good cut
> >through switch (like the big 3com ones) and you'll see why. For pure switching
> >the fancy dedicated hardware stuff beats us flat on latency and I guess always
> >will.
>
> Sure...hardware switches are gonna kick butt in switching...that's not
> really what I was talking about....you can take a Cisco router, and tell
> it to switch in all these ways...and some of these "switching" services
> are labeled so because they deal with things at the link layer, but are
> really only useful for routers, particularly in that group, VRRP.
Except for a MAJOR cisco problem with router "switching". If you use any
extended ACL's then you automatically CANNOT use the "switching"
structures. In fact the 75xx manuals etc (the only ones I sometimes
read...) specifically reccommend you not use ExACLs at all in a 75xx
platform if you want fast "switching" to occur anywhere in the box. So
here is an area where 2.4(perhaps)/3.0 Linux will have a decided
advantage. Talking with Rusty about netfilter and Alexey's fastroute it is
possible that we can have both simultaneously available which in current
2.2 is not possible. In this case we get to have essentially the same
"switching" capabilities as the Cisco AND we get to use much more powerful
packet filtering than the Cisco.
As added flame bait... - Currently as of 2.1.somethingorother when the
policy based routing was added the routing structures you can create with
Linux are only matched (barely) by IOS 12.x. Linux is somewhat unique in
that regard.
> To try to pull this back on topic some. :) I'd really like to see some
> more switching services added to Linux. VRRP would be one that would be
> really useful for folks to routing on Linux. I'd also like to see the
> bridging support extended to be more flexible. I have a really bizarre
> thought that would be really cool to be able to use IMHO. :)
Like the Lucent transparent firewall.... 8-}
> For a server system (you can do largely the same with a router system,
> but my use for this would be for a server system), put two nics in
> it...connect each nic to seperate network switches. Let the nics run
> briding code so they participate in spanning tree. Also "bridge" the
> traffic to a loopback or "virtual" interface or so (maybe you can
> already do this? haven't gotten a good answer, don't think so though),
> so you can tell daemons and such to bind to the loopback or virtual
> interfaces and the system can transparently recover from a dead nic card
> or cable, or switch.
>
> I've mentioned this to several people and quite a few of them just
> didn't understand what I was getting at...several others thought I was
> just weird (which is quite possible, even quite likely I'd say), and a
> few thought it was a neat idea.
I have spoken with several people who have wanted to do similar types of
functions. The real problem is that bridging (like switching in most
cases) sucks for real networks.
> Anyway...that's out there as a random idea for enhancement. :)
> --
> Jeff McAdams Email: [EMAIL PROTECTED]
> Head Network Administrator Voice: (502) 966-3848
> IgLou Internet Services (800) 436-4456
> -
Hmm - I heard attributed to Alan (please correct me) that "Alexey is a
one-mane Cisco deconstruction team" and from dealing with all of the
2.1/2.2/2.3 routing setups I swear by that statement. I am rapidly getting
to the point where I reccommend that even large scale routers (yes
including 75xx) can in many cases be supplanted by a well built Linux box.
And by well built I refer more to an embedded style system. I suspect that
even if someone took 2.2 and could create drivers for Cisco's hardware
that the linux kernel could run even or better than IOS.
But hey I am just a starry eyed dreamer... 8-}
--------------------------------------------------
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Paktronix Systems LLC
1506 North 59th Street
Omaha NE 68104
Phone: (402) 932-7250
Email: [EMAIL PROTECTED]
WWW: http://www.paktronix.com
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