Wireshark-users: Re: [Wireshark-users] 8-10% packet error/loss is normal wired network?
From: Flako <[email protected]>
Date: Wed, 11 Jul 2012 16:56:35 -0300
2012/7/10 Jim Aragon <[email protected]>:
> At 08:32 AM 7/10/2012, you wrote:
> Counting only "tcp.analysis.retransmission" I'm from 0.95% to 1.21%, a value
> more enjoyable. :)
> I think it's despicable for further research .. but I get the question if
> this value is normal :)
> In a wireless link, a loss of 1% is acceptable, but in a network cableda?
> I would expect lost packets within local traffic in a wired LAN to be close
> to zero; certainly under 0.5%. However, depending on the traffic levels on
> your network, if the 0.95% to 1.21% retransmissions are not causing a
> problem, it might not be worth your time to track down.
> If you do want to try to track it down, packets generally get lost at a
> network device, so go to your switches one at a time and capture
> simultaneously on both sides of the switch. If you see "previous segment
> lost" on one side of the switch, but not on the other, then that switch is
> dropping packets. The same for any other network devices that the traffic
> passes through, such as routers or firewalls.
> If you can't capture on both sides of the switch simultaneously, then
> there's another method to identify the point of packet loss. Find a TCP
> retransmission, then apply a display filter for the tcp stream index number
> and the TCP sequence number. If you see both the original packet and the
> retransmission, then the packet loss was downstream from you. If you see
> only the retransmission, but not the original packet, then the packet loss
> was upstream from you. Be sure to do this for several retransmissions. As
> you identify whether packet loss was upstream or downstream from you, you
> can keep moving your capture point until you find the device that is
> dropping packets.
> You also said that you have a 100mps switch and a 1Gbps switch.  Are these
> switches directly connected to each other? If so, I'd start with the 1 gbps
> switch. If the 1 gbps switch is receiving traffic from the attached devices
> faster than 100 mbps, then it will be forced to drop packets because it
> can't transmit the packets to the other switch any faster than 100 mbps. In
> other words, it will be receiving packets faster than it can send them, and
> at some point, the switch's buffers will fill up and it will have to drop
> packets.
> Jim

Hello Prigge, Jim
The printer is at 100Mb / s FULL with autonegotiation disabled, the
desktop was as 1Gb / s FULL with autonegotiation enabled.
The swicth A (100Mb / s) and B (1Gb / s) are connected directly to each other.

Now connect the Desktop Printer and a switch C (only two), then swich
C connects directly to swicth A.
I'm sniffer on the Desktop to see differences and discard things. I
tell them when finished.

Thank you for writing so far.
(Examples of how to find a fault will serve me now or the next)