OT: Anyone know how to create network latency?!

gtvlusso

Something that we usually try and avoid, but I need to create a latency for a test - need to create some TCP timeouts....

Any ideas - using Linux LDAP and SOAP....

jds_1981

Can't physically unplug the wires?

gtvlusso

Nope - boxes are in Germany! And that just gives you a disconnect!

cee

can you configure the router or switch so that the TCP timeout is so small that it always does before the receipt is passed back to the originator?

Pufftmw

Check latency whilst uploading or downloading a number of 100mb files?

Check latency whilst transfering big files to the site in Germany and back?

Check latency whilst throwing an attack on your firewall?

Install a dodgy NIC?

UndercoverElephant

Set the default gateways along the way to take a circumambulatory route. Or even getting setting them up to route in a crcle and setting the max hops to a huge value...

dodgy

Adjust MTU size f at least one of the routers on the way. Make it very small.

waddlie

I would recommend re-setting the bipolarity on the transponster, myself.

Failing that - Ctrl, Alt, Delete.

kelsen

Just go for a ride on your bike and the problem will resolve itself

mzm70

Agree with dodgy, if you can ifconfig the local ethernet MTU size that should reflect back to the stack/application as MSS, if you can control the TCP send/receive window size then setting it down will require more acks/line trurn-around

Irvinet

Depends how serious a test you need. We ended up renting a 350km spool of fiber to test SAN replication latency over that distance....

gtvlusso

mzm70 wrote:

Agree with dodgy, if you can ifconfig the local ethernet MTU size that should reflect back to the stack/application as MSS, if you can control the TCP send/receive window size then setting it down will require more acks/line trurn-around

May screw up my SSH session to a box I have no way of resetting! Was hoping to be able to buffer packets recvd by the NIC....

SimonAH

Reverse polarity, throw the third switch!

cee

Can you put a box in the way?

on linux, run netem which as it suggests...does network emulation..you can mimic latency etc....

OR on FreeBSD....try dummynet...

same thing really.

davis

You can play with "tc" -- the traffic control manager for your network stack. It's probably already available for your distro.

If you need lots (and lots) of control, then I believe you can use iptables to limit it to certain traffic, although the only use I've seen of iptables for latency is to implement QoS to reduce latency on certain kinds of traffic.

Wow, this *is* OT :-)

Edit: Ah, knew I'd seen it before: LagFactory looks to be a useful wrapper around tc, though I've not actually used it.

noisemonkey

set network to download 100 torrents

pbrown1969boy

setup http://wanem.sourceforge.net/ and use it as your gateway

greg66_tri_v2.0

Have you tried turning it off and back on again?

If that doesn't work, try reinstalling Windows and all your applications.

(What? Isn't that the IT department's standard advice?)

itboffin

if you have cisco routers each end then an extended ping test with variable sweeping packet sizes, that will lay down a world of hurt on any WAN connection.

If not use a tool like iperf to generate a massive amount of bi directional traffic across the link then run you latency test at the same time, once the network overload is over your session will return to normal.

again with the cisco end to end WAN safe guard yourself by setting the routers to reload 10 mins after your test ends, just in case you kill the devices (unlikely) you can always log back in and cancel the reboot.

As for your SSH sessions you're using screen or byobu aren't you?

itboffin

Greg66 wrote:

Have you tried turning it off and back on again?

If that doesn't work, try reinstalling Windows and all your applications.

(What? Isn't that the IT department's standard advice?)

ssssh old man, is that nurse I hear? back to bed now you have finger painting in the morning.

Norky

cee wrote:

Can you put a box in the way?

on linux, run netem which as it suggests...does network emulation..you can mimic latency etc....

OR on FreeBSD....try dummynet...

+1. netem here and +1 to wot davis said.

Code written to simulate various network failure conditions is the way to go. Other methods are a little... clunky.