[c-nsp] Maximum traffic on Gigabit Ethernet

[Peter Rathlev]

On Mon, 2011-10-03 at 16:47 +0300, Manaf Al Oqlah wrote:
> What is the maximum traffic that a gigabit Ethernet interface can
> handle on Cisco 7600 router RSP720-3C-GE before dropping packets . we
> are able to reach 750 mbps / 125 mbps input/out rate!

It would depend on what kind of line card you use to push the traffic
and what the box is doing other than this, since the ports can be
oversubscribed. Assuming the box is doing nothing else you should have
no problems pushing a gig through it both ways.

If you see less than this there might be several reason. The devices
sending/receiving might not be able to keep up. Or if the traffic is
bursty you might see drops. You can verify the latter with

 show queueing interface GigabitEthernetX/Y | begin Packets dropped

for both interfaces the traffic traverses. You could also use "show
interface GigabitEthernetX/Y | incl drops" for a more terse display.

Keep in mind that there's some protocol overhead. A "full" ethernet
frame of 1538 bytes (including preamble etc.) can carry a TCP segment =
payload of 1448 bytes (assuming you use timestamps), and if you measure
the speed in "mebibits" (2^20 bits) you would have a maximum theoretical
"speed" of about 876 Mib/s (~931 Mb/s) in a TCP session on a Gigabit
link.

-- 
Peter