munna

I have had it....i look at my 3com switches almost everyday...and all I see is amber package collision lights flashing.its mesmerizing

the flashing is every 10 maybe 20 seconds!!it on all of the stacks.we are using the 3300mm switches

any ideas chaps?i am thinking rogues network cards..print servers..but the cards that we have got onsite are the accton NIC cards..unlike the 3com NICs there is no config tab..so all you do is plug in..install driver and away you go!!CRAP

stevem2k

pull one of the connections in turn until the collisions go away.

_some_ collisions are inevitable on a busy network - there shouldn't be any real issues until you are getting loads...

Steve

dogmaul

you shouldn't get any collisions on a switch !! you sure they aint hubs ?? you could try using ntop if you have a Linux box or any good sniffer to find out what is flying round and causing the collisions

munna

i thought about the switch/hub thing....just confirmed it they are all 3300mm and SM's...they have a bank of lights for connection status...then a bank of lights for packet collisions...they are all flashing away like there is no tommorrow!!

dsmith

Errr.... Just 'cos its a switch doesnt mean you shouldn't get packet colliisions. There are still 2 devices (Switch + NIC) attempting to use the same bit of ethernet. Collisions are good - collision are an important part of how Ethernet works. If you don't like collissions get Token-Ring instead

While it is arguable you shouldn't get collissions on a Full-duplex connected device the collision light may also inidicate other "errors" unaffected by full/half duplex. If you believe you may have a problem, either check the port error counts on the switch or if there aren't any - get a better switch that does

Deano

Edit: So how many different spellings of collision can I get in 1 paragraph

[Edited by dsmith - 7/3/2002 3:11:44 PM]

munna

thought as much!!...cheers gents...will put that at the bottom of my priority list!!...things to do?...set up an email system..set up the intranet page...rebuild a server..(NT4)...go home and get drunk!!...which order will be the best?

i just thought of the question after seeing the lights..(No Not UFO's)

will keep you posted

DavidRB

From the ethernet section of Daryl's TCP/IP Primer:

"Ethernet is like a bunch of loud people in an unmoderated meeting room. Only one person can talk at a time, because communication consists of standing up and yelling at the top of your lungs. People are allowed to start communicating whenever there is silence in the room. If two people stand up and start yelling at the same time, they wind up garbling each others' attempt at communication, an event known as a "collision." In the event of a collision, the two offending parties sit back down for a semi-random period of time, then one of them stands up and starts yelling again. Because it's unmoderated, the likelihood of collisions occurring increases geometrically as the number of talkers and the amount of stuff they talk about increases. In fact, networks with many workstations are generally considered to be overloaded if the segment utilization exceeds 30-40%. If the collision light on your hubs is lit more often than not, you probably need to segment your network. Consider the purchase of a switch..."

dogmaul

that's why I said are you sure its a switch due to the fact they don't broadcast very much so reduces the amount of packets hitting each other the packets only go where they are supposed to go so you send packet from pc sat on port 1 to port 80 it goes straight there on a switch but on a hub it sends the same packet down all 79 other ports. Im lucky i have a fully switched network 4 x 80port hp procurve 4400 and 2 x 25 port 2425

dsmith

So no Windows on the Network then ?

Switches forward all broadcasts to all ports on that LAN (or VLAN). Routers Don't. Layer 2/Layer 3 differences and all that.

On any half-duplex link (10 meg or 100meg) even with just 2 devices you will get collisions. This is not a problem it is how Ethernet works. However it is obviously better to minimize the time any segment is in "collision" hence switches are good. Some NIC drivers (e.g. Intel) actual vary the inter-frame gap to reduce collisions in a busy environment but this can actually impact peformance on a switch connected device as the driver can be a little too conservative and would be better off sacrificing the odd collision for more aggressive timing and better throughput.

If you never see a collision light then you are not getting the best throughput from your network - but - on a very busy ethernet segment (e.g. hub or half-duplex switch attached device) increasing collisions is why practical throughput is limited to about 40% of the link speed.

Also, as I said, some switches use the "collision" light as a general "collision/error/bad packet" light. If one particular port appears to flash more than others when you feel it shouldn't there may well be NIC putting ****e on the LAN. One of the by-products of a good switch is that this sh*te will go no further so should not impact anything else - but as I said the switch error counters should tell you this.

Now if only IBM hadn't maintained its stranglehold on Token-Ring for so long and someone had managed to create cheaper T-R NIC chipsets we could all be using a proper LAN technology.....(Ahhh the hours spent tracking down a beaconing nic, listening to the "clunk" of a relay in an IBM MAU)

Deano

tntsystems

Hey dogmaul, the words "lucky" and "HP" dont fit in the same sentence mate stick with cisco

dogmaul

suppose but as i struggled to get this place to move off smc 10mb hubs i consider myself very lucky

munna

as i said before gents...they are most definatly switches!!..as i said 3com 3300sm and 3300mm..3300xm...all interconnected using matrix cables...they even say the word SWITCH on them...

i thank you all for trying to help...you have been of great assistance...i think though that DSMITH may have hit the nail on the head!!

thank you gents....may the force be with you..(Sorry could not help but drop that one in!!)

^Qwerty^

Read this about how networks work if you want a laugh:

http://www.lorry.com/Docs/pixie.html

dsmith

LOL - enjoyed that link so mailed it to a few colleagues - one of whom apparently used to work for the bloke who wrote it.

Umpteen billion people on the internet and its still a scarily small world....

Deano

Mr.M

CD is a good indication of very busy network, but as other people have said those lights could mean anything. You might have framing errors, crap signals, noise on one of your connections.

Suggest you get a sniffer / packet analyser to look at the trafic on your lan.

Reminds me of the time one lousy NIC kept intermitingly storming the network and brought down the switch.... Ah those where the days!

carl

Let's get this straight -- you're getting a collision light every 10-20 seconds (i.e. 3-6 lights a minute) and you're worried

As an aside, the theoretical maximum throughput of unswitched Ethernet is only 27%.

Token Ring is nice, but FDDI is nicer

dsmith

But with FDDI there aren't any relays to go "clunk" - how are you supposed to fault find that then ?

carl

As long as all your stations are dual-attached, it doesn't matter if it goes wrong

munna

true....so I should not be worried?..i must admit...we have no logon degradation...no file save problems...no internet problems (2x2 meg ADSL connections...one for the users one for the IT department...which consists of ME...only me....ha..ha..ha..haheee..heee)all the servers are fine...IIS and the intranet site are fine....the girls are mighty fine!!...sorry

thank you to one and all

dsmith

Monitor thr situation by proactively testing the throughput and latency of the port and link under investigation using real world test applications.

i.e. Carry on surfing scoobynet until you spot a problem

gunnerstkd

I think ur accton NIC cards doesn't support full-duplex communications, thus, the switch and the nodes are communicating in half-duplex. Full-duples eliminates collision though coz it turns the connection to be point-to-point. And I suppose.. wow... ur network is so active.. so many collisions occuring..

hmm.. or i guess ur NICs doesn't support autonegotiation and it's running on full-duplex and ur switch is set to run on half-duplex.. or vice-versa, thus, it might attempt to transmit data at the same time that the switch is attempting to transmit data, thereby causing data collisions

cheerios

IT

I agree with everyone!!

Sounds like a device somewhere is maybe running H/Duplex into the switch, you could probably use the management features on the switch to tell you which one.

It could also be a bad packet, noise etc as suggested throughout the thread.

But most importantly, if it's only avery half a minute, stick something over the collision light so you can't see it, quit worrying and surf some more scoobynet :-) :-)

munna

cheers guys....i will do what you say...first off to find some masking tape...second stay on scoobynet all day...third..go home early!!...i feel awful...spent all day @manchester airport yesterday...my inlaws are over here....1st time in england...we live in the heart of the lake district which you have to admit is gorgeuse(Cannot spell.sorry)...so the 1st thing they see when we are driving up the motorway...is Bradford...thats where they are statying for the 1st 2 months of their stay...1st impressions always last ey?

oh well Tania and Nitika.(my wife and daughter are down in bradford for 2 months!!...I see a trip to the Dam coming up!!