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switch duplex problem/vlan

By D_unafraid ·
HI All
First thank you for your time
I have having two Network Issue with my customer, please help me if you can

I have a new cisco 2950 edge switch connected to a existing 6500 Core switch. the Core switch is hard set to 100mbps full, the strange thing is I cant hard set my edge switch to 100mbps, they cant see each other on the network.The customer insisted that the Core must be hard set to 100mbps, and that left me with no other choice.I try troubleshooting the switch and realised that only by setting the edge to auto or 100 half will I get them to talk, but then again, due to the different setting on the switches, i am receiving alot of collsion. what can i do about it? what are the usual problem that causes the switch duplex difference

my customer complained to me when they try to transfer files across just one of the vlan, the transfer was cut off after a while. files transfer to other vlan segment was fine. where else can i start looking into to solve the problem?

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by Nico Baggus In reply to switch duplex problem/vla ...


Yep this is a big problem almost never noticed...
Half duplex is the old way of the internet, all
devices politely waiting for a gap and then try
to send something... Nothing wrong with it, when
a collision occurs (it is detected by having the
sender receive anything it sends itself, when
there is a mismatch there is a collision) both
will back off a random time and then try again...

Full duplex means you known you are the only one
on a pait of wires, so you can send at will, the
receiver will get it.

When a Full duplex port talks to a half duplex
port the half duplex side will only talk WHEN
there is NO trafic for the duration of sending a

The problem will show when having massive
Telnet sessions and the like will probably show
no delay etc. (not enough trafic to push the half
duplex side away.)
BTW the interface on a 2950 can certainly be set
to full duplex, but you have to think these are
IOS devices. ( conf t <NL> interface fe x/y <NL>

It will show on the Full duplex side with a lot
of CRC errors, and RUNTS as well as receiver
If you cant get it working FD, the force set it
to HALF duplex on both sides.!!!!
Auto is almost allways a bad choice, because it
might work but also might go wrong any time.

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by Nico Baggus In reply to

BTW, the dropping of network connections can be
easily be caused by this kind of phenomenon.
Like sayd before reset all counters and then
review all counters after a weeks work. The
misfits will show themselves with high errors on
runts, crc and receiver.

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