Date: Thu, 19 Sep 1996 12:39:37 -0500 (CDT) From: Joe Greco <jgreco@brasil.moneng.mei.com> To: dennis@etinc.com (Dennis) Cc: jfarmer@sabre.goldsword.com, hackers@FreeBSD.ORG Subject: Re: Routers - hardware received wisdom Message-ID: <199609191739.MAA11243@brasil.moneng.mei.com> In-Reply-To: <199609191531.LAA12464@etinc.com> from "Dennis" at Sep 19, 96 11:31:14 am
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> You could easily run 2 T1 on a 386....Joes machine has 2 ethernet cards
> in it, which adds an extra 10Mbs of bandwidth.
:-) Dennis :-) Yeah, but that's a PCI 486DX5/133. :-)
See the other thread about this.
Your limit is generally how much work the CPU needs to do. At some point,
ISA bus bandwidth becomes a consideration, but I doubt it will become a
consideration before CPU does on a 386.
I highly recommend you consider ET's products... they use DMA transfers
and basically work like Ethernet cards from a "system overhead" point of
view. Very efficient... much more so than some others I have looked at.
The CPU you save by using DMA can then be used for Real Work such as
actually routing the packets someplace.
My _best_ suggestion is to try it and see how it works. You can always
upgrade motherboards if CPU time becomes a problem.
% vmstat 1
procs memory page disks faults cpu
r b w avm fre flt re pi po fr sr f0 w0 in sy cs us sy id
0 0 0 35124 660 1 0 0 0 0 0 0 0 1111 52 9 2 41 57
0 0 0 35124 660 1 0 0 0 0 0 0 0 861 52 8 1 33 66
0 0 0 35124 660 1 0 0 0 0 0 0 0 1211 62 13 1 56 43
0 0 0 35124 660 1 0 0 0 0 0 0 0 1268 52 9 1 54 45
0 0 0 35124 660 1 0 0 0 0 0 0 0 976 78 13 1 38 61
0 0 0 35124 660 1 0 0 0 0 0 0 0 854 65 11 1 34 65
0 0 0 35124 660 1 0 0 0 0 0 0 0 1116 55 10 1 46 53
0 0 0 35124 660 1 0 0 0 0 0 0 0 763 52 8 1 25 75
0 0 0 35124 660 1 0 0 0 0 0 0 0 634 52 9 0 15 85
0 0 0 35124 660 1 0 0 0 0 0 0 0 661 52 8 2 15 83
0 0 0 30956 660 1 0 0 0 0 0 0 0 718 52 9 0 25 75
0 0 0 35124 660 1 0 0 0 0 0 0 0 488 58 9 1 11 89
0 0 0 35124 660 1 0 0 0 0 0 0 0 659 52 8 1 15 84
0 0 0 30948 660 1 0 0 0 0 0 0 0 763 52 9 0 20 80
0 0 0 30948 660 1 0 0 0 0 0 0 0 640 62 8 1 17 83
0 0 0 30948 660 1 0 0 0 0 0 0 0 639 52 8 2 16 83
% netstat -I ed0 1
input (ed0) output input (Total) output
packets errs packets errs colls packets errs packets errs colls
231 0 159 0 0 392 0 392 0 0
108 0 132 0 0 242 0 242 0 2
220 0 172 0 0 398 0 399 0 5
193 0 135 0 0 328 0 327 0 1
292 0 164 0 3 458 0 458 0 7
295 0 174 0 1 478 0 477 0 8
317 0 192 0 0 511 0 510 0 7
221 0 163 0 0 386 0 386 0 4
168 0 138 0 0 307 0 312 0 1
274 0 150 0 0 427 0 427 0 3
134 0 150 0 0 285 0 285 0 1
105 0 97 0 0 204 0 204 0 0
102 0 115 0 0 219 0 219 0 3
107 0 121 0 0 230 0 230 0 0
66 0 64 0 0 135 0 134 0 0
82 0 98 0 1 182 0 182 0 1
129 0 141 0 0 275 0 275 0 2
The snapshots should be within a few seconds of each other...
Anyways this is a 386DX/40 with six SMC ISA Ethernet cards in it. You
can see that there is a fair amount of traffic flowing through it, and
even so it is pretty idle. The traffic is mainly a mix of NNTP and
various other traffic, so the packet sizes tend to be smaller than
if you were just doing FTP and Web traffic...
I personally get nervous when I see idle < 70% or so.
You can basically stick as many interfaces in a machine as you want,
just as long as the traffic does not swamp the machine. That is a
function of several variables:
o Number of interfaces
o Average traffic on each interface (less = better)
o Average packet size (larger = less CPU utilized)
o Machine speed and bus speed (most easily adjusted variable)
o OS speed (relatively constant)
Once you understand the concept that you could support a million
56K lines with the CPU power of an HP-35 as long as nobody tried
to send any traffic, you have mastered the concept.
I really encourage you to _try_ it.. stress test it.. and draw your
own conlusions. That is really the best answer.
... JG
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