adding hubs to managed switch issues

[jjohnsoncantell]

Greetings,

 

We have a lot of offices where there isnt the infrastructure to support additional desktops and in these offices we have no choice but to use hubs. We use netgear 5/8 pt switches however when these are used they cause no end of problems for the computers running off them. We also loose the ability to connect to and monitor wireless points and printers that are connected to them.

 

I realise that adding hubs to managed switches isnt a good idea but can anyone explain to me why we have this trouble? Should I be buying a different type of hub/switch?

 

Many thanks

James

[3s-gtech]

Hubs aren't switches - which are you using? If it's hubs, throw them away! If switches, do you know how many hops you have back to the servers/core? What exact devices are you using?

[Jamo]

Comes down to the difference between hubs and switches. Hubs effectively broadcast all unicast traffic out of all interfaces as it is not 'intelligent' at traffic management like a switch is. On busy links this can make traffic soooooooooo busy! Coupled with the collision domain problem of hubs it would not be surprising that a wireless point, which is in itself a shared medium, would fail to perform adequately.

 

Un-managed switches would be better, 5 port switches aren't too expensive and are far better than hubs, however neither can replace a managed switch for ease of management down the line!!

[Davit2005]

As previous member wrote.

 

Shouldn't really be an issue using hubs unless their are other performance issues caused by how hubs work but I can't see that unless you have one huge network causing too much traffic, hubs at basic are merely multiport repeaters, whatever goes in one port goes out every other unlike switches that have basic intellegence and can forward based on MAC tables.

 

Have you different vLANS setup for Wireless, Printers or management which aren't supported by the netgear switches? You could also see wether the ports are set to auto speed on connected uplink switch ports to help rule out any compatibility issues.

Edited October 5, 2012 by Davit2005

[Geoff]

Due to the broadcast issues mentioned above, managed switches will sometimes deem the port the hub is connected to as 'broken' due to a 'broadcast/arp storm'. You will need to turn this functionality off on the relevant ports of your managed switch if it's detecting this problem and isolating the ports because of it. On HP ProCurves it's known as loop protection. Be aware that if you do disable this that you are vulnerable to your network segment being taken out by sloppy network patching. As you're buying hubs rather than fitting extra wall sockets I don't expect you have the change control procedures to prevent this either?

[Michael]

It sounds to me you have a switch, but then you're daisy chaining other smaller switches together. Hubs are a thing of the past really and as far as I'm aware, you cannot buy them new anymore.

 

Hubs essentially share available bandwidth of 10 or 100Mbps, whereas switches give a dedicated 100Mbps per port. This is the simplest way to understand how it works.

 

You can buy high density 24 or 48 port switches and this would fit into a 19" rack, which is the industry standard. You can spend anywhere between a few hundred pounds to thousands depending on your needs.

[jjohnsoncantell]

Hi Guys.

 

We have a procurve backbone across 4 blocks running trunked fibre between the blocks. Procurve 5406zl in each block running to the data points. In a lot of offices we're then running clients off of netgear unmanaged gs608 and fs605 switches due to lack of data points. Ive run traceroutes back to the dc and getting one hop replies.

[jjohnsoncantell]

They must be picking up some kind of broacasts as the switches are always busy even when the machines have been idle for some time. All the activity lights flash in unison suggesting to me its something being recieved as opposoed to sent

[CyberNerd]

Should I be buying a different type of hub/switch?

 

 

You should be buying a cabling contractor.

 

These stupid netgear things cause no end of issues. I've banned them from my network.

[jjohnsoncantell]

pfi school unfortunately so it costs a bomb

[Jamo]

Traceroutes only class a hop as traversing a routable interface, so it would always report one hop to clients on your local subnet.

 

Only thing you could try is wireshark the interfaces from the connected clients, see if there is rogue traffic

[Davit2005]

As Jamo says,

You say you are getting a HOP, As Jamo says, this suggests to that you have some sort of routing going on maybe between vLANS.

 

Switch ports may show some activity (1 or 2 blinks a second) when any device connected to it has power to it you shouldn't get huge ammounts as that might suggest a loop.

Edited October 5, 2012 by Davit2005

[Jamo]

Switches may show some activity when any device connected to it has power to it.

 

You say you are getting a HOP, this suggests to me that you have some sort of routing going on maybe between vLANS.

 

You always get one, its the end device

[jjohnsoncantell]

Thanks for your replies guys. Never used wireshark before, looks quite deep, is there a beginners guide as such>

[Jamo]

Thanks for your replies guys. Never used wireshark before, looks quite deep, is there a beginners guide as such>

 

I think the beginners guide is about as good as their motto:

 

Go Deep

 

Monitor it for a bit and check the packets you are recieving. If they are for other clients (barring the broadcast and multicast addresses) then you may find that the unmanaged switches just arent man enough for the job.

 

Its quite a task running wireshark, best bet really is to monitor a good port vs a bad port i suppose otherwise you won't have a baseline to monitor against.

[twin--turbo]

Wireshark will only pickup broadcast packets and unlearned destinations if the switch is unmanaged as there will be no way to turn on port mirroring.

 

Rob

[Jamo]

Wireshark will only pickup broadcast packets and unlearned destinations if the switch is unmanaged as there will be no way to turn on port mirroring.

 

Rob

 

Yup that is no problem though. If you ARE recieving 'unlearned' destinations then that means that you are recieving a lot of spam OR that the MAC tables are full in the unmanaged switch

[twin--turbo]

Are the "links" forced to the correct speed/duplex settings. I had a big issue where our core and an edge switch we both flappign about autonegotiating.

 

Force the managed switch to 100 or 1000 full duplex rather than auto and see if that clears up some of the garbage.

 

Rob

[twin--turbo]

By the looks, the FS605 only has a 1024 Mac table, so given the client devices including printers ap's etc. And switchport MACS that may be learned also. Then yes the MAC table may well be getting full.

 

Rob

[oxide54]

pfi school unfortunately so it costs a bomb

 

isn't privatization supposed to introduce competition and in turn value. on sorry this pfi!

 

i totally understand where your coming from, I've had to really put my foot down over daisy chained switches. it really is hard work sometimes though,

[twin--turbo]

isn't privatization supposed to introduce competition and in turn value. on sorry this pfi!

 

i totally understand where your coming from, I've had to really put my foot down over daisy chained switches. it really is hard work sometimes though,

 

HA.....

 

We had a full new install with cisco kit at our other site, twin 4507 cores and distribution and edge switches. It took 5 months to get the UN/PW out of the BIG installer. The day I got the details I swore so much the air turned blue. Our expensive network was using switches daisy chained 7 levels deep and with no redundancy. It took three months for them to agree that it was abysmal and come in and do it properly.

 

Rob

[oxide54]

ours isn't like that there is structured cabling to every room, and 2 cores and links to edge switches in cabinets which the structured cabling goes to, its just the always want machines where there is no points or 10 machines where there is only 1 point. we do all the IT ourselves, network kit I decided and installed, no installer or anything, but we have to get structured cabling installed by the PFI/FM people in the same we have to get them to supply desks, other wise they refuse to clean them, and everything costs 40x the normal price and takes 100x as long.

 

I can remember working in a normal company, where we had a budget, phoned a guy got a quote and sent him a PO. a week later we had data points installed. why does everything need to be so fricking uneccessarily difficult in education, it is not by accident