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Subnetting to limit broadcast traffic


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#31 sc302

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Posted 02 April 2013 - 15:23

If you are not using dropbox on your lan you may want to disable the lan sync portion of it. That will shut down that broadcast chatter.


#32 +BudMan

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Posted 02 April 2013 - 15:44

1.2.3.9 ?? That is out of place - you got some sort of misconfiguration there for sure. 1.2.3.9 is a APNIC range that is for research under the debogon project? Pretty sure you should not be seeing traffic from that IP on same wire as your 192.168 network ;)

You should only ever see traffic from IPs in the same range on the same wire - if your seeing other networks on the same wire your setup wrong! ;) You should not run more than one address scheme on the same wire.

#33 OP Unrealism2k

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Posted 02 April 2013 - 15:51

lol, ya I am 176. =)

I actually am not seeing much broadcast I suppose other then from me. I guess really maybe just fixing the subnet so I can have more IP's is really the only thing left I need to adjust.

When you subnet, let's say I do have broadcast issues... I assume since 192.168.1.*, and 192.168.2.*, etc. are on the same subnet so therefore that would not fix that issue if it was broadcast, am I understanding that part? However if I had one on a subnet of 255.255.255.0, and the others on 255.255.252.0 they would ease broadcast traffic if that was the issue? And of course a router in between so they could talk to each other correct?. Just so I understand is all, maybe its not the broadcast. I might look back into the switch about VLan and separate the phones somehow at least.

#34 +BudMan

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Posted 02 April 2013 - 16:01

255.255.255 or /24 and 255.255.252 or /22 are not really subnets those are you masks.

so for example 192.168.3.0/24 is a subnet of 192.168.0.0/22

If you wanted to use the /22 space, then you could subnet that down to 4 /24's

192.168.0.0/24
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24

If all your looking to do is get more address space - then you could change your current 192.168.1.0/24 to /23 and then you could use addresses of 192.168.0.1 to 192.168.1.254 were 0.0 would be wire and 1.255 would be broadcast.

I would look into that 1.2.3.9 thing though.. And sure looks like from your screen shot your switch has voice vlan support so you could put your phones on their own vlan different than your PCs and other devices.

This would limit your broadcasts to devices on the same vlan. But not really seeing that much broadcast there -- if your saying your having issues with the network maybe get a sniff while the issue(s) happen - maybe you are seeing a broadcast storm during that period?

But even a /23 should not cause you much issue with broadcast unless you have some really really chatty broadcast applications running.. I didn't see any real noise there like you saw in mine where browsers were broadcasting for espn.com, etc. ;) The dropbox stuff could be removed real easy - unless your using it for local sync between machines? Then your going to want to keep that on, if not turn it off - its a pretty chatty broadcaster.

And just for general tidiness I would disable PCs from being able to be master browsers - it can cause trouble with the browselist if you have machines that can be the browser and enter and leave the network often, they end up thinking they are the browse master and causing an election - it can mess with your browselist being up to date, etc. You really should turn that off on all but machines that are on your network 24/7 -- normally I would suggest you turn it off on all PCs!! And even on servers other than your DC(s) could turn it off as well. You only need 1 box on your network to maintain the browse list - and the DC should win the election anyway - so there is no real reason for other boxes to even participate in the process.

As to other broadcasters - I saw a few other ips running dropbox other than yours. And curious what that 1.2.3.9 thing is ;) Let me look up the mac if listed in your screenshot.

#35 Teebor

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Posted 02 April 2013 - 16:08

HDMI cables for stacking has been around for a little while, but its not that uncommon now. We have several Dell switches here which use HDMI for stacking.
The biggest problem is making sure you have a good enough quality cable otherwise you can experience all kinds of funkiness like really poor data rates :(

If you have Cisco Switches the good news is that a lot of polycom phones support CDP so that would make putting things in to the correct VLANS a bit easier.
Also this document might provide some information - http://supportdocs.p..._guide_v2_2.pdf
There is a section on using DHCP to set VLAN membership

If you are using Netgear and that image above is one of your switches you can clearly see a section for setting a voice VLAN and another for VLAN so it would be a case of setting the Voice VLAN and the data VLAN and then setting the correct VLANS on the phones.

At the end of the day I think you are going to need to set up a test network with your equipment to play around with and test as you appear to be a bit unsure and I would not recommend proceeding blindly

#36 sc302

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Posted 02 April 2013 - 16:09

Might want to enable port mirroring to capture the packets across your network instead of just your computer and the broadcast....

http://www.downloads..._UM_15Jun09.pdf
Page 7-22 to 7-24

#37 +BudMan

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Posted 02 April 2013 - 16:15

well you don't have that 1.2.3.9 thing highlighted so can not see what mac it has to look up the maker of the nic, but its running dropbox ;) curious!

I agree with teebor, if possible setup a lab to play with! Do you have an extra switch you can use?

edit: Also can be very useful to have a span port setup as sc302 mentioned, most likely is at gateway of your network (port connect to your router) is good spot. This can give you an idea of what is leaving your network, users doing stuff maybe they shouldn't be doing - eating up your internet bandwidth, etc. Good place to spot unwanted applications on your network, you could setup a box running ntop or something to give you a breakdown of protocols in use, top talkers, etc.