What I say is that You actually see the same packet, but the tag You see on eth3 is not there on the "logical" interface eth3.2 (The tag-info is used to put it on the correct VLAN-interface, and stripped)... The same thing happends on the other interface - the eth4 physical interface "holds" all VLAN traffic, where traffic on one of the VLANS appears untagged on the logical interface eth4.2...
:-)
Johan
----- Original Message -----
From: Cyprian Clement
To: VLANFORGE
Sent: Monday, April 04, 2005 11:32 AM
Subject: Re: [VLAN] VLAN Packet sent twice
Johan,
Thanks for your reply. just one quick question to the point you made. Are you actually saying if eth3.2 is sending out a packet(say to eth4.2) the packet would first reach eth3 as normal UnTagged packet but then eth3 will add a Tag(802.1q) before that packet goes out to the destination(eth4.2) ?. Then at the destination eth4 will be the first to receive the 802.1q packet and then stripp off the 802.1q before forwarding the packet to eth4.2. As a result eth4.2 will receive it as a normal UnTagged packet ?.
Sorry if I misinterpreted your point.
Regards,
Cyprian.
-------------
Johan Henes <johan@xxxxxxxx> wrote:
Hi Cyprian !
On the physical interface (eth3) ALL packets on the trunk arrives (logically enough). Here they are tagged with 802.1q info... Then the packets are "placed" in the correct VIRTUAL interface with the 802.1q info stripped away....
This is why You expeirience what You do...
Best regards,
Johan
----- Original Message -----
From: Cyprian Clement
To: VLANFORGE
Sent: Monday, April 04, 2005 10:02 AM
Subject: Re: [VLAN] VLAN Packet sent twice
Hello All Again,
As a follow up to what I mentioned earlier regarding the same packet on eth3 and eth3.2, I should also have mentioned the following:
-When I monitor(using ethereal) just the eth3 I see a Tagged(VLAN) Packet being sent from it and it shows the source address as 51.1.2.2. However, when I monitor eth3.2 I see an UnTagged(no VLAN) Packet sent from it and it also shows the same source IP of 51.1.2.2.
Should this not be the other way arround. I would expect the monitoring of eth3.2 to show VLAN and eth3 to UnTagged(no VLAN) packet. Does the internal Linux handling of the VLAN justify what I am seeing?
Thanks,
Cyprian.
-------------
Cyprian Clement <cyprian_clement@xxxxxxxxxxx> wrote:
Hi Ben,
To answer your question, all I observe on the ethereal is as follows:
Source Destination
51.1.2.2 51.1.20.2
51.1.2.2 51.1.20.2
Now when I click on one of them I see a packet with VLAN Tag but when I click on the second one I see exactly the same packet(same seq number, SSRC, and Timestamp) but without a Tag(i.e. without .1q). From this I deduce it's the same packet but sent differently. Not sure whether it's actually sent twice or once simply once but one of them is stripped off .1q
Any Comments?
Regards,
Cyprian.
------------
Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote:
Cyprian Clement wrote:
> Hello community,
>
>
>
> I have a query regarding packet transmission in the VLAN arena. First,
> let me give a picture of the configuration I have:
>
>
>
> Eth3 eth4
>
> Eth3.2 eth4.2
>
>
>
> I have assigned eth3.2 an IP of 51.1.2.2 and eth4.2 an IP of 51.1.20.2
>
>
>
> A call is made from 51.1.2.2(i.e. eth3.2) to 51.1.20.2(i.e. eth4.2). The
> issue I have noted is that when monitoring a call via ethereal I see
> that the same RTP packet is being sent twice. However, one of the packet
> is has a VLAN Tag while the other one has no Tag but both of them go to
> the same address.
>
>
>
> -The question is why is this the case? i.e. why do we have same packet
> t! ! ! wice; one Tagged while the other Untagged?
>
> -Is it fair to assume that the Tagged packet goes to eth4.2 while the
> Untagged one goes to eth4 ?
>
> -If this is the case does it mean eth3.2 originates the same packet
> twice? Or it's simply that the same packet is being sent twice but one
> by eth3(Untagged) and the other by eth3.2(Tagged) ? I wonder why this
> would be the case though.
Are you sure it's being sent twice, or are you watching the same packet traverse
the .1q interface and then the physical interface on the way to the wire?
Ben
>
>
>
> As always, Thank you in advance.
>
>
>
> Regards,
>
>
>
> Cyprian.
>
> ------------
>
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>
>
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>
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--
Ben Greear
Candela Technologies Inc http://www.candelatech.com
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