It looks like you're trying to add an 802.1Q header with VLAN 9 and
sending the packet to an access port. That's not how access ports
work. The FAQ explains the basics of VLANs.
Q: What's a VLAN?
A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
partition a single switch into multiple switches. Suppose, for
example, that you have two groups of machines, group A and group B.
You want the machines in group A to be able to talk to each other,
and you want the machine in group B to be able to talk to each
other, but you don't want the machines in group A to be able to
talk to the machines in group B. You can do this with two
switches, by plugging the machines in group A into one switch and
the machines in group B into the other switch.
If you only have one switch, then you can use VLANs to do the same
thing, by configuring the ports for machines in group A as VLAN
"access ports" for one VLAN and the ports for group B as "access
ports" for a different VLAN. The switch will only forward packets
between ports that are assigned to the same VLAN, so this
effectively subdivides your single switch into two independent
switches, one for each group of machines.
So far we haven't said anything about VLAN headers. With access
ports, like we've described so far, no VLAN header is present in
the Ethernet frame. This means that the machines (or switches)
connected to access ports need not be aware that VLANs are
involved, just like in the case where we use two different physical
switches.
Now suppose that you have a whole bunch of switches in your
network, instead of just one, and that some machines in group A are
connected directly to both switches 1 and 2. To allow these
machines to talk to each other, you could add an access port for
group A's VLAN to switch 1 and another to switch 2, and then
connect an Ethernet cable between those ports. That works fine,
but it doesn't scale well as the number of switches and the number
of VLANs increases, because you use up a lot of valuable switch
ports just connecting together your VLANs.
This is where VLAN headers come in. Instead of using one cable and
two ports per VLAN to connect a pair of switches, we configure a
port on each switch as a VLAN "trunk port". Packets sent and
received on a trunk port carry a VLAN header that says what VLAN
the packet belongs to, so that only two ports total are required to
connect the switches, regardless of the number of VLANs in use.
Normally, only switches (either physical or virtual) are connected
to a trunk port, not individual hosts, because individual hosts
don't expect to see a VLAN header in the traffic that they receive.
None of the above discussion says anything about particular VLAN
numbers. This is because VLAN numbers are completely arbitrary.
One must only ensure that a given VLAN is numbered consistently
throughout a network and that different VLANs are given different
numbers. (That said, VLAN 0 is usually synonymous with a packet
that has no VLAN header, and VLAN 4095 is reserved.)
On Sat, Mar 16, 2013 at 12:46:10PM +0800, Fang wrote:
> May be my understanding is wrong.I tried ovs-ofctl add-flow br0
> cookie=1,nw_src=192.168.0.11,nw_dst=192.168.0.33,ip,actions=mod_vlan_vid=9,output:6
> ("6" is tap3),and failed.
> Could you give me an example please.Thank you.
>
>
>
>
>
>
>
>
> At 2013-03-15 23:09:07,"Ben Pfaff" <[email protected]> wrote:
> >On Fri, Mar 15, 2013 at 06:52:33PM +0800, Fang wrote:
> >> Hello.I have three VMs on my host.
> >>
> >> Bridge "br0"
> >> Port "br0"
> >> Interface "br0"
> >> type: internal
> >> Port "tap1"
> >> tag: 7
> >> Interface "tap1"
> >> Port "tap2"
> >> tag: 7
> >> Interface "tap2"
> >> Port "tap3"
> >> tag: 9
> >> Interface "tap3"
> >> Port "eth0"
> >> Interface "eth0"
> >> ovs_version: "1.7.1"
> >>
> >> I want to make vm1 communicate with vm3 by modifying the vlan tag.
> >>
> >> VM1(tap1):192.168.0.11
> >> VM2(tap2):192.168.0.22
> >> VM3(tap3):192.168.0.33
> >>
> >> I set
> >> ovs-ofctl add-flow br0
> >> cookie=1,nw_src=192.168.0.11,nw_dst=192.168.0.33,ip,actions=mod_vlan_vid:9,NORMAL
> >> but it did not work.
> >
> >This does not work for packets coming from vm1 because vm1 has an access
> >port, not a trunk port, so "normal" drops packets that have 802.1Q
> >headers.
> >
> >> I tried
> >> ovs-ofctl add-flow br0
> >> cookie=1,priority=10,in_port=4,dl_vlan=7,actions=mod_vlan_vid:9,NORMAL
> >> ("4" is port tap1)
> >> and I also tried dl_src,dl_dst.All did not work.
> >
> >This does not work because packets received from vm1 do not have an
> >802.1Q header, thus "dl_vlan=7" will not match them.
> >
> >You will need to write a rule that matches the packets you want and then
> >sends them directly to their destination, rather than trying to go
> >through "normal".
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