Can't See Packets from Clients

Alcatel / Speedtouch adsl modem
December 11, 2009 at 03:02:10
Specs: Linux, Intel C2D
Hi all,

I have a Intranet in which some clients are using UTP cabling & some clients are connected thru ADSL modem by centralised DSLAM in Telephone Exchange. The modems are working on Bridge mode.
Now I want to monitor my network traffic by Ethereal/TCPDUMP etc. But they show packets from UTP connected PCs only not ADSL connected PCs. Same thing happens if i use Network Monitoring Software on ADSL connected client. Then it shows only packets to & from That particular PC to Gateway Server only.
I dont want to use my Gateway to do this job.
I think the ADSL modem is blocking the Broadcasted packets thats why I cant see it from other clients.

Any Idea..!
Ravinder Singh

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December 11, 2009 at 04:12:07
I don't think, that it's a lack of broadcast pakets.
Broadcast is normally that, what you always get.
If the PC, where you run Ethereal, is connected to a switch, you can only see broadcast and nothing else, because the network pakets are always directed to the port, where the request came from.
So therefore, you need to use a HUB between the switch and the ADSL device. So you can connect the monitoring PC also to that HUB and can sniff all the traffic from you network to the ADSL and vice versa.
You also have to install PCAP, to sniff pakets with Ethereal, to switch the network card into the promiscious mode.

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December 11, 2009 at 05:41:28
Broadcasts can't pass bounderies and be seen beyond their broadcast domains.

Google "broadcast domain" and do a bit of reading and I'm sure you'll understand better.

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