RE: gigabit router (was Re: Getting a "portable" /19 or /20)

From: Craig Partridge []
Sent: Tuesday, April 10, 2001 4:36 PM

>Don't be absurd, I can walk into fry's and pick up a motherboard with
>64bit/66mhz PCI, some Netgear GA620's, and all the other
>components for a 1GHz computer for under $1000.

OK, so your bus has 4.2 Gb/s of bandwidth. But, alas, you're in a PC
so you have to copy each packet from the line card, into main memory,
examine it, and push it back out to a line card. So each
packet consumes
twice its size in bus bandwidth. So 2 1 Gb/s line cards will consume
4 Gb/s backplane. Assuming you can run the PCI at full rate (which in
my experience is a big big if), you can connect two Ethernets.

There are a few server-class motherboards that have dual PCI-66 buses. One
on each bus and there's no problem. Incidently, those same MBs usually have
dual or quad CPUs.

Incidentally, this isn't the full story either. You have to
do a route lookup on each of those packets. That's typically 5 to 10


accesses... 5 memory access times 1 Mpps per gigabit times 2 gigabits
is 10 million lookups per second or 100 ns per lookup. Allowing for
time spent getting through the chip to the pins, you probably
need 60 or 70ns DRAM, which is doable. Except, oops!, that completely


your memory bandwidth... where are you going to find the cycles to
get the packets in and out?

Huh?! We haven't had the 60ns limitation for over three years. What
time-vault have you been living in? PC100 RAM is error correcting at 10ns
and PC133 runs at ~8ns. In fact, I challenge you to show me where you can
even buy 60ns RAM these days. That's right up there with 3 GB HDDs, not
available because they can't find customers for any thing that small/slow,
except propriatary applications (they make you pay ... large). I just paid
$104 for 256MB of ECC PC100 RAM, at the local computer store. The discount
wasn't even worth the gas/hr to drive down to San Jose for (1989 Chevy
Suburban, in San Jose rush hour).

PS: Side note, this illustrates where router vendors earn their bucks.

Router vendors earn their bucks by building routing/switching appliances.
The fact that they manage to get corps to cough up $200K for $15K worth of
hardware (COGm, generous) is yet another issue. I expect to see some serious
price drops in the next 6 months. I also expect to see commodity hardware
start making some serious in-roads (cause of the price-drop).

COGr = 1/2 COGm, manufacturers cost of raw material (chips, labor, copper,
and such)
COGm = Cost of Goods manufactured (fully burdened)
2*COGm = The resellers cost (including mfg's margins)
4*COGm = The distributors price
8*COGm = Retail price (What you pay, full retail)

[yeah, that's right. This means that, said RAM, cost $13 to make. econ 101]

Find a way to move data over each bus only once (double your

Dual PCI66 bus.

Design your memory subsystems to keep packets and routing
data separate (increase your memory bandwidth!).

PC133 ECC RAM (8ns).

Find a processor that
doesn't waste cycles doing virtual memory (improve your memory access

Dual/Quad 1Ghz PIIIs, anyone?

Oh yes, and then add hot board swap,

How many routers actually do this? Even when they do, it is more prudent to
find the time to shut it down for 5 minutes. It's not like solid-state
devices die all the moving parts. Keep them cool and they'll go
obsolete before they fail. Unless it's a combat situation (where you don't
have time to swap anyway) there isn't much that warrants this level of
maintenance. You're much better off with a redundant hot fail-over
configuration so that you can bring one down for PM and replacement/upgrade.

a working BGP implementation (quick, where's Tony Li working these


I actually like GateD. It ain't fancy, but it works.

a CLI,

Linux is handy. RT Linux might be better (maybe).

and a power subsystem for a CO,

If you must include that, then my choice is a Liebert GT3600.

and you're in business.

With current commodity price drops, in less than 6 months, the cost of doing
this will fall well below $1000, retail. Considering potential market
volume. A 100% proprietary hardware solution may not be feasible, at that
price-point. They will *have* to use commodity hardware, just to keep up the

Dual/Quad 1Ghz PIIIs, anyone?

For routers, single fast CPU's, fast ram and fast PCI buses
work wonders, hence my liking the Alpha processor systems.
Mostly because of a really good PCI bus. On other lists
the discussions get real technical as to why, and a dual 800+
system is fast enough it does not matter... but unless the code
(Zebra/Gated/Routed) is designed to use multi-processors,
it does not help the router deamon. It will free up resources
for other tasks.

In playing around I summarize the differences as:

*nix boxen routers: Decent Hardware, Great OS, more than
enough CPU/RAM cheap to make up for differences in most cases.

Purpose built systems: GREAT hardware, Minimal OS tuned for the
application at hand (routing).

Funny thing is, I am typing this on a roof, using a 200mhz Linux
boxen with 2 nics used for wireless network routing... using SSH
and Xwindows while it routes packets for 2.4ghz DSSS and some 23ghz
(10mbps fdx) analog traffic. It's a great night to be babysitting the

I think as hardware and software evolve over time, all of these
arguments will fade into volatile ram.