Network Problems

PlexioUK used Ask the Experts™


We have a customer who is experiencing intermittent network issues.  They run 2 physically separate networks which access the internet via 2 separate broadband routers on separate broadband circuits.  One network runs their IT systems and the other runs a VOIP system using SIP trunks over ADSL.

Both networks experience the same problems, namely random slowdowns and general unresponsiveness on the IT network and broken/poor call quality and calls dropping on the VOIP network.

There are 3 PCs, 1  2003 SBS server on the IT network and 4 handsets and 1 Win 7 Pro PC (which runs 3CX VOIP software) on the VOIP network.  The 3CX PC and server are connected via an APC UPS.

Every piece of equipment on the VOIP network with the exception of the Snom 320 handsets has been changed along with the UPS over the past 8 months.

We have experienced hardware failures over the last 6 months as follows:

3 x routers
1 x Firewall
1 x PC
1 x UPS

We are pretty certain we know the cause of the problems, but would appreciate a second opinion.  I’m not going to put down our thinking here just for now so I don’t bias any replies!

Thanks in advance.
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Do you have the interface statistics for any of your interfaces on the network gear or maybe logs that have been generated that would point to a cause?

Do these issues happen at the same time all the time on both networks?

Are there any shared hardware components between the two networks?
Les MooreSr. Systems Engineer
Top Expert 2008

Sounds like a physical loop where someone accidentaly connected the two networks together...



 - We have some Wireshark analysis which shows a degree of latency in both networks when these problems occur, and yes it happens at the same time on both networks.  There is no physical link between the 2 networks with the expiation of the UPS, which has been replaced to try eliminate that from the equation, other than that they are totally independent and autonomous
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Prepare for the CompTIA Network+ exam by learning how to troubleshoot, configure, and manage both wired and wireless networks.

just a wild guess, but could it be that someone plugs in their laptop on the "pc" port of the snom, while working wireless , so mixing things up?

i've seen this happen once.

Also, do you mean both the server and 3cx box have 2 NICS to connect each one to the UPS?


Yes we wondered about that, but we already checked that no one was connecting anything into the Snoms.  The 3CX & server are only connected to the UPS via their power cables.  The NICs connect directly to the switch for each network from the box concerned
i see..
I see that you have a firewall replaced, where exactly does that fit in the network?
is it possible to draw a schema, so i can get a better idea?


From the top down the 2 networks are as follows:

VOIP Network

Netgear ADSL Router
Watchguard Firewall
Netgear Switch
3CX Box - Snom Handsets

IT Network

Netgear ADSL Router
Watchguard Firewall
Netgear Switch
SBS2003 – PCs/Laptops

The VOIP network works on static IPs and the SBS handles DHCP on the IT network
ok i have 2 questions,

why not 1 watchguard with multi-wan and 2 seperate lan on the same WG?

when you say slow network, do you mean LAN, or internet traffic?

also , the broken calls are internal or external calls?

sorry for all the questions but not so easy to determine something like this from distance.
also can you post a wireshark cap in txt format?
Thanks for all your help.  as it turns out, this issue  was power related&  affecting the whole site.  The utility company have now resolved this and the system now functions as expected.


The comment is self explanatory

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