Network Problems

Posted on 2011-09-05
Last Modified: 2012-08-13


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.
Question by:PlexioUK

Expert Comment

ID: 36484505
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?
LVL 79

Expert Comment

ID: 36485662
Sounds like a physical loop where someone accidentaly connected the two networks together...

Author Comment

ID: 36487555

 - 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
LVL 14

Expert Comment

ID: 36489621
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?

Author Comment

ID: 36489691
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
Maximize Your Threat Intelligence Reporting

Reporting is one of the most important and least talked about aspects of a world-class threat intelligence program. Here’s how to do it right.

LVL 14

Expert Comment

ID: 36489981
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?

Author Comment

ID: 36490167
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
LVL 14

Expert Comment

ID: 36490534
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?

Accepted Solution

PlexioUK earned 0 total points
ID: 37573242
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.

Author Closing Comment

ID: 37589603
The comment is self explanatory

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

I'm Dumb-phoned(ed) Last week, I noticed this message when adding events to my Google Calendar: On June 27th (2015), Google is removing SMS as a notification option for Google Calendar events.  Their assumption is that enough people have smart p…
Creating an OSPF network that automatically (dynamically) reroutes network traffic over other connections to prevent network downtime.
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Here's a very brief overview of the methods PRTG Network Monitor ( offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

760 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

19 Experts available now in Live!

Get 1:1 Help Now