Packet Fragmentation, MTUs, Thresholds & Home Network Reliability

[Lance]

Holy smokes, this home network stuff is becoming quite a hobby!

Linksys BEFW11S4 v2 wireless router and WMP11 wireless PCI cards.

My home network works OK. Updated to XP SP2 last week, (1 Home, 3
Professional, 1 wired, 3 wireless). Everyone can see everyone else. I
can ping, I can surf, I can share, I can VPN, I can RDC, I even have the
firewalls turned on. I even think I'm beginning to understand what I'm
doing.

So what's my problem?

My wireless connections have become unreliable in the past couple days.
Last night my son mentioned just sporadic internet connection for a
couple days. So I started normal trouble shooting procedures.

Drivers/firmware OK, firewall settings/exceptions OK. permissions OK,
user accounts OK, Simple File Sharing off (which is OK), signal strength
OK, connection speed 5.5-11 Mbps (used to be consistently 11 Mbps),
power saving feature off.

About the only thing I found outright wrong with the wireless setups are
that one computer was listening on Ch 11 when it should have been
listening on Ch 6. DHCP works fine, but surfing the internet was unreliable.

When pinging the problem became very plain. My main tool was using the
ping command like this:
ping 192.168.1.100 -n 4 -f -l 1472

I found the following:
- 50-100% packet timeouts
- packet fragmentation at anything more than 1272.

Linksys Knowledgebase had two suggestions.

For the good DHCP/bad internet surfing, reduce RTS and Fragmentation
Thresholds to 2304 (from 2432 and 2356 respectively) and beacon interval
from 100 to 50 on the router. I also manually modified these threshold
settings on each wireless card.

For the packet loss, reduce the router MTU to 1300 (1272+28). It was set
at "Disabled." There's no comparable setting for the cards.

This improved matters, but I'm still experiencing about 10% packet loss.

Why have things changed? I've never experienced packet losses like this
before. Was fooling with threshold settings and MTU a proper course of
action? What other troubleshooting steps can I take?

Thanks for you time,

Lance
*****

 

[Hans-Georg Michna]

Holy smokes, this home network stuff is becoming quite a hobby!

Lance,

you are so right!

When pinging the problem became very plain. My main tool was using the
ping command like this:
ping 192.168.1.100 -n 4 -f -l 1472

I found the following:
- 50-100% packet timeouts
- packet fragmentation at anything more than 1272.

Linksys Knowledgebase had two suggestions.

For the good DHCP/bad internet surfing, reduce RTS and Fragmentation
Thresholds to 2304 (from 2432 and 2356 respectively) and beacon interval
from 100 to 50 on the router. I also manually modified these threshold
settings on each wireless card.

For the packet loss, reduce the router MTU to 1300 (1272+28). It was set
at "Disabled." There's no comparable setting for the cards.

This improved matters, but I'm still experiencing about 10% packet loss.

You can reduce the MTU setting in your computers. Try that, use
the DrTCP program from www.dslreports.com.

However, if my router asked me to reduce my MTU setting to 1300,
you know what I would do? I would give that router a kick that
lands him in the garbage bin. Linksys hasn't been known for
particularly wonderful quality, so maybe you want to look for a
better router. A good compromise between quality and price is
the DrayTek Vigor series.

However, I might still have tried the MTU=1300 setting, out of
curiosity.

Why have things changed? I've never experienced packet losses like this
before. Was fooling with threshold settings and MTU a proper course of
action? What other troubleshooting steps can I take?

Good questions? I have no clue why the installation of SP2 could
have changed something here, but we can't rule it out.

Please have a look at http://www.michna.com/kb/WxNetwork.htm and
perhaps also at http://www.michna.com/kb/WxSP2.htm for more
thoughts.

Hans-Georg

 

[Lance]

Hans-Georg Michna thought carefully and wrote on 8/22/2004 1:01 AM:

Good questions? I have no clue why the installation of SP2 could
have changed something here, but we can't rule it out.

Please have a look at http://www.michna.com/kb/WxNetwork.htm and
perhaps also at http://www.michna.com/kb/WxSP2.htm for more
thoughts.

Hans-Georg

Thanks Hans-Georg, wonderful list of tips you have. I've bookmarked it.

I haven't solved the problem yet, but I think I've narrowed it down to
some kind of signal strength or quality problem that's developed
recently. A scan of available wireless networks doesn't show anything
besides my own network, I unplugged our wireless phone without any
change, so it must be something else.

Lance
*****