eth0 promiscuous mode

eth0 promiscuous mode

[Natarajan K]

HI,
	I am part of a LAN and get my IP through DHCP. Will eth0 interface be put in 
promiscuous mode initially or is there any option I should use to put it in 
promiscuous mode? I use Mandrake 8.2. 
-- 
Natarajan
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Re: eth0 promiscuous mode

[Ray Olszewski]

At 09:31 AM 8/30/02 +0530, Natarajan K wrote:
>HI,
>         I am part of a LAN and get my IP through DHCP. Will eth0 
> interface be put in
>promiscuous mode initially or is there any option I should use to put it in
>promiscuous mode? I use Mandrake 8.2.


Huh? You don't need your interface in promiscuous mode. Your system sends 
out a broadcast packet to request a DHCP lease, and the DHCP server 
responds with a lease offer using the MAC address of your host. You do need 
to run a DHCP client on your system ... dhcpcd, or dhclient, or pump (not 
sure that Mandrake uses) ... to request the lease.


--
-------------------------------------------"Never tell me the odds!"--------
Ray Olszewski					-- Han Solo
Palo Alto, California, USA			  ray@comarre.com
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Re: eth0 promiscuous mode

[Axel Siebenwirth]

On Thu, 29 Aug 2002, Ray Olszewski wrote:

> >interface be put in
> >promiscuous mode initially or is there any option I should use to put it in
> >promiscuous mode? I use Mandrake 8.2.

Very stupid question: What is the promiscuous mode? I think I see my NIC
going into that mode when I start tcpdump...

Thank you,
Axel
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RE: eth0 promiscuous mode

[Joseph Jackson]

wow how rude.  Why would you call his or anyone elses question stupid? if
you can't help you shouldn't reply to posts.

-----------------------Original Message-----------------------
>From:  Axel Siebenwirth [mailto:axel@hh59.org]
>To:  Linux Newbie [mailto:linux-newbie@vger.kernel.org]
>Date:  8/30/2002 12:09:00 AM
>Subject:  Re: eth0 promiscuous mode
>
>On Thu, 29 Aug 2002, Ray Olszewski wrote:
>
>> >interface be put in
>> >promiscuous mode initially or is there any option I should use to put
it in
>> >promiscuous mode? I use Mandrake 8.2.
>
>Very stupid question: What is the promiscuous mode? I think I see my NIC
>going into that mode when I start tcpdump...
>
>Thank you,
>Axel
>-
>To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>Please read the FAQ at http://www.linux-learn.org/faqs 

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Re: eth0 promiscuous mode

[Axel H. Siebenwirth]

Joseph Jackson wrote:
> wow how rude.  Why would you call his or anyone elses question stupid? if
> you can't help you shouldn't reply to posts.

I'm really sorry for my syntactical error. What I meant to be stupid was 
my question I asked ;) since I do not know what the promiscuous mode is.

When I read my mail after sending, I knew somebody would understand it 
this way. SORRY!

Best regards,
Axel




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RE: eth0 promiscuous mode

[Mojo Jojo]

He wasn't calling the otehr question stupid, he was saying i have a stupid
qustion as in he didnt know what promiscuosmsosus mode was....

easy tiger.......



> wow how rude.  Why would you call his or anyone elses question stupid? if
> you can't help you shouldn't reply to posts.
>
> -----------------------Original Message-----------------------
> >From:  Axel Siebenwirth [mailto:axel@hh59.org]
> >To:  Linux Newbie [mailto:linux-newbie@vger.kernel.org]
> >Date:  8/30/2002 12:09:00 AM
> >Subject:  Re: eth0 promiscuous mode
> >
> >On Thu, 29 Aug 2002, Ray Olszewski wrote:
> >
> >> >interface be put in
> >> >promiscuous mode initially or is there any option I should use to put
> it in
> >> >promiscuous mode? I use Mandrake 8.2.
> >
> >Very stupid question: What is the promiscuous mode? I think I see my NIC
> >going into that mode when I start tcpdump...
> >
> >Thank you,
> >Axel
> >-

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Re: eth0 promiscuous mode

[Ray Olszewski]

At 10:06 AM 8/30/02 +0200, Axel Siebenwirth wrote:
>On Thu, 29 Aug 2002, Ray Olszewski wrote:
>
> > >interface be put in
> > >promiscuous mode initially or is there any option I should use to put 
> it in
> > >promiscuous mode? I use Mandrake 8.2.
>
>Very stupid question: What is the promiscuous mode? I think I see my NIC
>going into that mode when I start tcpdump...


This is a list for beginners, so while your question may be naive, it is 
hardly stupid. I mention this because I was struck by the large number of 
people apparently interested in discussing your syntax, but themselves 
either unable or unwilling to include an *answer* to the question in the 
messages they posted. Shame on all of you.

Normally, the firmware in a NIC filters incoming traffic and passes to the 
OS only those Ethernet frames that are addressed to the NIC's hardware 
(MAC) address. When in promiscuous mode, the NIC firmware passes ALL 
Ethernet frames up the ladder, not just ones sent to its MAC address. 
tcpdump is probably the most common app that uses promisc mode, but there 
are others.



--
-------------------------------------------"Never tell me the odds!"--------
Ray Olszewski					-- Han Solo
Palo Alto, California, USA			  ray@comarre.com
-------------------------------------------------------------------------------

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Re: eth0 promiscuous mode

[David Yeu]

Ray Olszewski wrote:
>
> Normally, the firmware in a NIC filters incoming traffic and passes to 
> the OS only those Ethernet frames that are addressed to the NIC's 
> hardware (MAC) address. When in promiscuous mode, the NIC firmware 
> passes ALL Ethernet frames up the ladder, not just ones sent to its MAC 
> address. tcpdump is probably the most common app that uses promisc mode, 
> but there are others.

Don't mean to hijack the thread, but I have a related question:

Will promiscuous mode work properly if my computer is plugged into a 
switch? I've tried unsuccessfully to use tcpdump or tethereal to view
all the network traffic, but I'm always confined to traffic that either
originates or is destined to my machine (broadcasts too).  Or is it
perhaps the NIC?  Do all NICs have the ability to go into promiscuous
mode?

Thanks in advance.

Dave.

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Re: eth0 promiscuous mode

[Ray Olszewski]

See below.

At 11:18 AM 8/30/02 -0500, David Yeu wrote:


>Ray Olszewski wrote:
>>
>>Normally, the firmware in a NIC filters incoming traffic and passes to 
>>the OS only those Ethernet frames that are addressed to the NIC's 
>>hardware (MAC) address. When in promiscuous mode, the NIC firmware passes 
>>ALL Ethernet frames up the ladder, not just ones sent to its MAC address. 
>>tcpdump is probably the most common app that uses promisc mode, but there 
>>are others.
>
>Don't mean to hijack the thread, but I have a related question:
>
>Will promiscuous mode work properly if my computer is plugged into a 
>switch? I've tried unsuccessfully to use tcpdump or tethereal to view

Yes. Promiscuous mode *itself * still works properly, in that the NIC 
*itself* still passes on evey frame it sees.. But an app like tcpdump will 
not see all packets because the *switch* only sends out on the port to the 
NIC frames that are intended for the NIC's MAC address (or Ethernet 
broadcast frames).

Some switches (but not the cheap ones, like the one I have, and very likely 
the one you have, if you are a home user) have special ports that do 
receive all frames, just to permit traffic monitoring by sysadmins.

>all the network traffic, but I'm always confined to traffic that either
>originates or is destined to my machine (broadcasts too).  Or is it
>perhaps the NIC?  Do all NICs have the ability to go into promiscuous
>mode?

I don't know that *all* NICs can ... but I have never encountered one that 
cannot.


--
-------------------------------------------"Never tell me the odds!"--------
Ray Olszewski					-- Han Solo
Palo Alto, California, USA			  ray@comarre.com
-------------------------------------------------------------------------------

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Re: eth0 promiscuous mode

[Nathan]

Hi David,

> Will promiscuous mode work properly if my computer is plugged into a
> switch? I've tried unsuccessfully to use tcpdump or tethereal to view
> all the network traffic, but I'm always confined to traffic that either
> originates or is destined to my machine (broadcasts too).  Or is it
> perhaps the NIC?  Do all NICs have the ability to go into promiscuous
> mode?

that is really the point of a switched network. Switches are supposed to
be smart in that they learn about who is at what port and only repeat
broadcast traffic to everyone.

Cheers,
Nathan


> Thanks in advance.
>
> Dave.
>
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