Re: wi problem with message > 7400 bytes

On Thu, 30 Oct 2003, Lars Eggert wrote:

> Daniel Eischen wrote:
> >>
> >>Could you post a tcpdump for each case? I wonder if this is related to a 
> >>fragmentation issue I've seen in the past.
> > 
> > 22:46:43.513038 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52198:1480_at_0+)
> > 22:46:48.522475 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52199:1480_at_0+)
> > 22:46:53.532018 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52200:1480_at_0+)
> > 22:46:58.541178 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52201:1480_at_0+)
> > 22:47:03.553048 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52202:1480_at_0+)
> > 22:47:08.568862 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52203:1480_at_0+)
> > 22:47:13.583328 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52204:1480_at_0+)
> > 22:47:18.578512 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52205:1480_at_0+)
> > 22:47:23.609098 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52206:1480_at_0+)
> > 22:47:28.597680 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52207:1480_at_0+)
> > 22:47:33.607059 gpz.foo.bar.com.38340 > vespa.12345: udp 7393 (frag 52208:1480_at_0+)
> 
> It's not what I've seen in the past - but also pretty strange! Only the
> first fragment seems to be received. Wonder what happened to the other
> fragments...
> 
> If you tcpdump on gpz, does the output look the same? Also, you may want

I'll try that tomorrow.  gpz is a Sun Solaris 9 box at work, but
before you say "try another BSD box", I already did.  I tried
2 other FreeBSD boxes in place of gpz and I had the same results.

> to run the tcpdump without a filter (if you don't do this already) to
> see if the other fragments show up as corrputed frames or something.
> 
> (As an aside, fragmentation on a lossy link compounds throughput issues,
> but of course you know that already.)

Everything is behind Cisco 10/100 switches and doing 10/100
full duplex except for the laptop (vespa) which is through
a Dell TrueMobile wireless access point.  The access point
is connected to a switch and is about 10 feet away from the
laptop.

I tried this test at home with a different setup:

  orion - laptop with D-Link DWL-650H PC-Card (wi)
  sirius - FreeBSD current box with em interface
  Linksys WRT-54g router/access point with builtin 10/100 switch

There is no other traffic on this network; orion and sirius
are standalone.  sirius is wired to a 10/100 port in the
router/access point and is at 100 full-duplex.

Repeating the same test lets me send messages up to 25152
bytes in length, much better than 7400.  This seems to be
about the same limit I hit in VxWorks (which supposedly
has the BSD 4.4 IP stack).

I'll see if I can get my hands on a different access point
at work to see if that makes a difference.  Here's the
tcpdump from the above setup with message size 25153:

05:27:59.632708 sirius.49245 > orion-home.12345: udp 25153 (frag 19970:1480_at_0+)
05:27:59.815829 sirius > orion-home: udp (frag 19970:1480_at_1480+)
05:28:00.023248 sirius > orion-home: udp (frag 19970:1480_at_2960+)
05:28:00.216317 sirius > orion-home: udp (frag 19970:1480_at_4440+)
05:28:00.404066 sirius > orion-home: udp (frag 19970:1480_at_5920+)
05:28:00.583116 sirius > orion-home: udp (frag 19970:1480_at_7400+)
05:28:00.777315 sirius > orion-home: udp (frag 19970:1480_at_8880+)
05:28:00.950056 sirius > orion-home: udp (frag 19970:1480_at_10360+)
05:28:01.129616 sirius > orion-home: udp (frag 19970:1480_at_11840+)
05:28:01.327645 sirius > orion-home: udp (frag 19970:1480_at_13320+)
05:28:01.560564 sirius > orion-home: udp (frag 19970:1480_at_14800+)
05:28:01.769612 sirius > orion-home: udp (frag 19970:1480_at_16280+)
05:28:01.945923 sirius > orion-home: udp (frag 19970:1480_at_17760+)
05:28:02.128897 sirius > orion-home: udp (frag 19970:1480_at_19240+)
05:28:02.309202 sirius > orion-home: udp (frag 19970:1480_at_20720+)
05:28:02.514941 sirius > orion-home: udp (frag 19970:1480_at_22200+)
05:28:02.731612 sirius > orion-home: udp (frag 19970:1480_at_23680+)
05:28:02.907988 sirius > orion-home: udp (frag 19970:1_at_25160)
05:28:07.982121 sirius.49245 > orion-home.12345: udp 25153 (frag 20226:1480_at_0+)
05:28:08.150171 sirius > orion-home: udp (frag 20226:1480_at_1480+)
05:28:08.357960 sirius > orion-home: udp (frag 20226:1480_at_2960+)
05:28:08.551270 sirius > orion-home: udp (frag 20226:1480_at_4440+)
05:28:08.754906 sirius > orion-home: udp (frag 20226:1480_at_5920+)
05:28:08.953891 sirius > orion-home: udp (frag 20226:1480_at_7400+)
05:28:09.145286 sirius > orion-home: udp (frag 20226:1480_at_8880+)
05:28:09.365111 sirius > orion-home: udp (frag 20226:1480_at_10360+)
05:28:09.577964 sirius > orion-home: udp (frag 20226:1480_at_11840+)
05:28:09.795675 sirius > orion-home: udp (frag 20226:1480_at_13320+)
05:28:09.973760 sirius > orion-home: udp (frag 20226:1480_at_14800+)
05:28:10.167432 sirius > orion-home: udp (frag 20226:1480_at_16280+)
05:28:10.362543 sirius > orion-home: udp (frag 20226:1480_at_17760+)
05:28:10.559922 sirius > orion-home: udp (frag 20226:1480_at_19240+)
05:28:10.775048 sirius > orion-home: udp (frag 20226:1480_at_20720+)
05:28:10.937800 sirius > orion-home: udp (frag 20226:1480_at_22200+)
05:28:11.115078 sirius > orion-home: udp (frag 20226:1480_at_23680+)
05:28:11.300522 sirius > orion-home: udp (frag 20226:1_at_25160)

-- 
Dan Eischen