Wireshark · Wireshark-users: Re: [Wireshark-users] Multicast problem

[Lars Lars <laasunde@xxxxxxxxxxx>]

Thank you for the quick response.

The code that configures the nic and handling receiving multicast is the same for server and clients. So it does not make sense for the server to fail and the clients to work. Also, the current code has worked fine for several years. The case being mentioned is the exception.

Will look into promiscuous mode tomorrow morning.

Cheers

> Date: Thu, 30 Oct 2008 21:24:21 +0100
> From: jaap.keuter@xxxxxxxxx
> To: wireshark-users@xxxxxxxxxxxxx
> Subject: Re: [Wireshark-users] Multicast problem
>
> Hi,
>
> That's called promiscuous mode. In that mode the MAC filter is disabled letting
> all packets come through to the driver layer, where the capture stub can get
> them. You can unselect this mode when you start a capture and see what your
> server does then.
>
> If I recall correctly it's a socket option in your application to get your own
> multicasts back. Otherwise make sure the application joins the multicast group
> it sends on, so to get the MAC filter in the NIC setup to receive multicast.
>
> Thanx,
> Jaap
>
> Lars Lars wrote:
> > Thank you for the response.
> >
> > It sounds reasonable that the server nic shortcuts the multicast. Is
> > there a way to verifying this shortcut since it does not appear to be
> > valid in at least one instance.
> >
> > After more debugging it appears that when wireshark (or windump) listens
> > to the server nic this affect the nic and triggers the server
> > application to receive the multicasts. By stoping wireshark to listen to
> > the nic, then the server application also stops receiving the
> > multicasts. What possible changes to the nic does wireshark perform when
> > listening to the traffic and could any of them explain the problems we
> > are having.
> >
> > Appreciate any input.
> >
> >
> >
> > ------------------------------------------------------------------------
> > From: robert@xxxxxxx
> > To: wireshark-users@xxxxxxxxxxxxx
> > Date: Thu, 30 Oct 2008 12:54:14 -0400
> > Subject: Re: [Wireshark-users] Multicast problem
> >
> > Your switch may allow you to span the traffic either in, out, or both.
> > Both is default on a Cisco switch if you do not specify. This assumes
> > you have access to the network, and Wireshark is running on an
> > independent platform. The interface driver on the server NIC may
> > shortcut the multicast before it has to get on the wire and come back.
> >
> >
> >
> > Robert D. Scott Robert@xxxxxxx <mailto:Robert@xxxxxxx>
> >
> > Senior Network Engineer 352-273-0113 Phone
> >
> > CNS - Network Services 352-392-2061 CNS Receptionist
> >
> > University of Florida 352-392-9440 FAX
> >
> > Florida Lambda Rail 352-294-3571 FLR NOC
> >
> > Gainesville, FL 32611 321-663-0421 Cell
> >
> >
> >
> > *From:* wireshark-users-bounces@xxxxxxxxxxxxx
> > [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] *On Behalf Of *Lars Lars
> > *Sent:* Thursday, October 30, 2008 12:22 PM
> > *To:* wireshark-users@xxxxxxxxxxxxx
> > *Subject:* [Wireshark-users] Multicast problem
> >
> >
> >
> >
> > Hello
> >
> > I'm new to this mailinglist and I'm hoping to get some help on a
> > specific problem I'm trying to debug.
> >
> > An server application is setup to send udp multicast message every
> > second. There are a number clients, including the server itself, that
> > listen for this messages. This has worked fine for several years. Then
> > this week I found an installation where all clients received udp
> > multicast message except the server. So the multicast is not echo'ed
> > back to the itself. (There is no firewall on any of the computers)
> >
> > By starting Wireshark 1.0.4 I'm able to monitor the multicast
> > messages\packages
> > Source: 172.21.1.1
> > Destionation : 230.21.1.200
> > Protocol: UDP
> > Source port:14800
> > Destionation port: 14800
> >
> > What I'm not able to understand is how can I debug this problem using
> > wireshark? How can I figure out if a particular udp multicast packet
> > is actually both sent and received by the same computer? Does this
> > application enable me to do so? Can someone please explain how
> > I could go about doing so, or recommend any other utility that might aid me.
> >
> > Thanks for your time. Appreciate any input.
> >
>
>
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