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Internet Bandwidth and Broadcasting on LAN

Amit Dixit_2
Regular Advisor

Internet Bandwidth and Broadcasting on LAN

Hi,
I am having a 512kbps bandwidth of internet
connection using DSL technology, in 1:3
ration shared medium.

But the problem is I dont get proper
bandwidth the service provider says that my
LAN is having to much of broadcasting.

Is there any tool thorugh which I can check ?
the braodcasting.

My LAN Includes Winx 9X clients, Windows NT
server and a Linux mail server

Few of the clients are having static IP and
few of them are obtaining Ip through DHCP.

How should I check broadcasting.
Apart from this after few hours the DSL
router doesnt pings the next hop as well
and my internet goes down entirely.

Thanks,
Amit.
17 REPLIES
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Why not try to analyse frames using a tcpdump or ethereal, filtering only broadcast packets ? You'll see how numerous they are...

hth

J
You can lean only on what resists you...
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

how to configure ethereal or tcpdump for the same and how come I will know abt it through the output of the above softwares.

thanks,
amit
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Could you describe slightly more your network configuration so I could suggest where to get this capture done (how many machines, connected thru switch or hub, router's position).

Tks.

J
You can lean only on what resists you...
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,
Thanks allot.

I am having 1 Cisco, 1 Dlink and 4 3Com
Switches. All are cascaded to cisco.

All users are connected to the Dlink or
3Com Switches.

The Cable DSL modem is terminated on Dlink.
Since it does'nt negotiate with CISCO.

The WINNT Server's and Linux Server Plus
HP Network Printer is also connected to
Cisco Switch + 2 Users.

All clients are running Windows 95/98 and
only TCP/IP is the protocol we are using.

Thanks,
Amit
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,

So I woudl start by installing ethereal on any D link connected windows client.
You'll get it here :
http://www.ethereal.com/download.html
You'll need to install before winpcap, which you'll find under windows installer section.
Launch a capture and filter by destination address... you'll see all broadcasts, and which machines they come from...

Tell if you have trouble with ethereal...

hth

J
You can lean only on what resists you...
Olaf Borowski
Respected Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Amit,

If you have a decent switch, the internal counters of that switch will give you information about broadcast packets on each port (the Cisco box will do definetely do that). Use the CLI or a MIB browser to get access to those values. Looking at those values, try to figure out how many broadcast packets you see per second or over a certain period of time. This will give you a good indication of what is going on.

Olaf

Stuart Teo
Trusted Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Hi Amit,

Just a quick question. Why should local broadcasts matter? They don't get routed across the DSL router anyway and should have nothing to do with the sluggishness you're facing.

"This side" of the DSL router and "That side" are 2 seperate broadcast domains. Aren't they?
If a problem can be fixed, there's nothing to worry. If a problem can't be fixed, worrying ain't gonna help. Bottom line: don't worry.
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

100% agree with Hwee Liang Teo... that's why I'm suggesting this ethereal : I am wondering what kind of broadcast can be routed and slow Internet connection, and even preventing you from getting next hop...
I had this kind of trouble twice, the first time, it was in fact some NetBios calls under b nodes that were filling router stack up, but the other time, it was my ISP not respecting its promisses...
Checking at frame level should get us know...
You can lean only on what resists you...
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,
I am sending an screeshot of ethereal.
Please have look at it andd tell me is my
network suffering from too much
broadcasting.

The machine 192.168.1.5 in the screen shot
is my linux server running sendmail using
LDAP.

And all the clients are running netscape.

Please see the attachment and give me your
valueable suggesgtions for the same.

Thanks,
Amit.
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,
Sorry forgot to mention that the strange
thing i observed is that braodcasting
from clients is for 192.168.1.5 which
itself is running DNS services for LAN.

Thanks,
Amit.
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,

All the broadcasts I see on your screenshot are ARP broadcasts. The more services a server run, the more it'll be searched through ARP broadcast, so searches on 192.168.1.5 are normal.
Still I do not see any ARP reply on your screenshot, you should have them somewhere, don't you ? Maybe could you optimize your LAN on letting compaqc0... and Acctontec4... machines to have larger ARP stack (if you need to know how, tell us what OS theses machines run), but this has no impact on your Internet connection, as ARP broadcasts are not forwarded by routers... So I wonder what broadcasts your ISP is talking about...
It would be worth asking him, and see if you router copnfiguration could be the cause of the problem... Can you see if it's routing is static or dynamic, and if it's RIP ?

J
You can lean only on what resists you...
Peeyush
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi Amit,

R u on fiber or satellite internet connection.......
- start ping google.com -t and ping google.com -t -w 999 ::u will see difference...and high letency.
- install MRTG for ur router and switch :: will show u exact figure for ur bandwith usage and comsuption..

i was having same problem but was in control after conf SQUID proxy for internet on linux and restricting all user to go out of network directly.. and problem stops after we switched to fiber network for internet

- when none of users r online try FTP and downloading :: see what speed u r getting and at what u starts getting RTOs(request timed out)

Regards,
Peeyush
http://geocities.com/peeyush_maurya/
any suggestion for my site.. http://geocities.com/peeyush_maurya/
Patricio_6
Occasional Visitor

Re: Internet Bandwidth and Broadcasting on LAN

Having same problem,
i have 8 windows 2000 server and there are a least 4 of this sending ARP packets, that are taking about 20 % of traffic, therefore my lan is a little slow.

My 2 DC are making a lot of this (ARP).
I have 80 win2k pro clients, but my clients are not making ARP request.

Thanks for your help.
Stuart Teo
Trusted Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Amit,

Your screen shot shows a lot of who-has broadcasts. who-has broadcasts are normal in a Ethernet environment. That's part of the ARP (address resolution protocol).

HP switches has a feature called ABC (automatic broadcast control) that will do a ARP reply on behalf of the Ethernet host.

This would confine all who-has ARP requests to within the switch itself. I'm not convinced that the who-has has anything to do with your slowness but this is worth a shot.
If a problem can be fixed, there's nothing to worry. If a problem can't be fixed, worrying ain't gonna help. Bottom line: don't worry.
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,
Thanks to all of you but I still dont know
what is wrong with my systems.

I am facing few very strange problems.

The machines on the LAN are running Windows
9X clients, when they access internet they
work fine for 2 hours but after that it
goes of but i am still able to access
LAN and still able to ping the DSL modem.

If I reboot the machine I am again able to
access the internet, and this goes on with
almost every machine on the network.

Apart from this please tell me are there
any tools to monitor congestion on switches
I am having Cisco-2900, DLink-DES-1024R,
3Com Super Stack II 3300 Switches.

Please tell me how to configure MRTG.

thanks,
Amit.
Jerome Henry
Honored Contributor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,

According to what you describe, your trouble seems to be more a config problem.
What DNS server do you use ?
Are your clients under dhcp ?
What gateway is set ?
Do you use wins ?
Do you use Netbios ?

As for mrtg, please use this link for install tutorial :
http://netmeas.asti.dost.gov.ph/docus/mrtg/Page2.php

hth

J
You can lean only on what resists you...
Amit Dixit_2
Regular Advisor

Re: Internet Bandwidth and Broadcasting on LAN

Hi,
Ok let me explain you the entire scenario.

I am having and ADSL connection to internet
1 Windows 2000 Server Running as PDC
2 Windows NT server
1 Windows 2000 Server Running Mcafee AV
Server

I am using Class C Internal Subnet
192.168.1.*

Few of my clients are having static IP's
those who access internet through ADSL
router whose IP is 192.168.1.1, and this is
the gateway IP for all those machines who
are having static IP.

Apart from this all users are having DHCP.

I am not using WINS though I have
configured.

Any other information you need please ask.
I am having 110 clients running win 95/98

Thanks,
Amit.