[ovs-discuss] Trunk & Vlan tag with ovsbr0,eth0 and vnet0
ashish yadav
ashishyadav78 at gmail.com
Fri Oct 4 05:10:58 UTC 2013
Hi Ben,
I have gone through OVS FAQ , but not able to understand Scenario 3 from
FAQ.
So could you please help me in same ?
Thanks & Regards
Ashish
On Fri, Oct 4, 2013 at 10:16 AM, Ben Pfaff <blp at nicira.com> wrote:
> The results you explain in all of your scenarios are what I would expect
> to happen. Did you read the introduction to VLANs in the OVS FAQ?
>
> 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 Fri, Oct 04, 2013 at 10:12:08AM +0530, ashish yadav wrote:
> > Hi,
> >
> > Could anyone please look into these fundamental queries of OVS & Vlan
> and
> > reply ?
> >
> >
> > Thanks & Regards
> > Ashish
> >
> >
> > On Thu, Oct 3, 2013 at 9:42 PM, ashish yadav <ashishyadav78 at gmail.com
> >wrote:
> >
> > > Hi,
> > >
> > > I was doing some exercise, came across few scenario.
> > > I need help to understand these cases.
> > >
> > > *Environment: *
> > > a. One Host and one VM in it
> > > b. OVS running:
> > > [root at sholay ashish]# ovs-vsctl show
> > > 2b113c03-81e5-4c90-ba6c-b2eb2381432a
> > > Bridge "ovsbr0"
> > > Port "ovsbr0"
> > > Interface "ovsbr0"
> > > type: internal
> > > Port "vnet0"
> > > Interface "vnet0"
> > > Port "eth0"
> > > Interface "eth0"
> > > ovs_version: "1.4.6"
> > >
> > > VM is up and I am able to ping:
> > > a. External World from VM & Host.
> > > b. Ping between HOST & VM fine.
> > >
> > > *Scenario 1:*
> > > vnet0 is vlan tag:
> > > [root at sholay ashish]# ovs-vsctl show
> > > 2b113c03-81e5-4c90-ba6c-b2eb2381432a
> > > Bridge "ovsbr0"
> > > Port "ovsbr0"
> > > tag: 0
> > > Interface "ovsbr0"
> > > type: internal
> > > Port "vnet0"
> > > tag: 5
> > > Interface "vnet0"
> > > Port "eth0"
> > > tag: 0
> > > Interface "eth0"
> > > ovs_version: "1.4.6"
> > >
> > > a. From VM, not able to ping Host machine & External world.
> > > b. From Host, able to ping External world.
> > >
> > > This is desired behaviour. No problem here.
> > >
> > >
> > > *Scenario 2:*
> > > ovsbr0 & vent0 are Vlan Tag:
> > > [root at sholay ashish]# ovs-vsctl show
> > > 2b113c03-81e5-4c90-ba6c-b2eb2381432a
> > > Bridge "ovsbr0"
> > > Port "ovsbr0"
> > > tag: 5
> > > Interface "ovsbr0"
> > > type: internal
> > > Port "vnet0"
> > > tag: 5
> > > Interface "vnet0"
> > > Port "eth0"
> > > tag: 0
> > > Interface "eth0"
> > > ovs_version: "1.4.6"
> > >
> > > a. VM is able to Ping host, but Fail to ping External world.
> > > * Why it is so ?*
> > > b. Host Machine Fail to ping External world.
> > > *Why its is so ?*
> > >
> > >
> > > *Scenario 3:*
> > > eth0 & vent0 are Vlan Tag:
> > > [root at sholay ashish]# ovs-vsctl show
> > > 2b113c03-81e5-4c90-ba6c-b2eb2381432a
> > > Bridge "ovsbr0"
> > > Port "ovsbr0"
> > > tag: 0
> > > Interface "ovsbr0"
> > > type: internal
> > > Port "vnet0"
> > > tag: 5
> > > Interface "vnet0"
> > > Port "eth0"
> > > tag: 5
> > > Interface "eth0"
> > > ovs_version: "1.4.6"
> > >
> > > a. VM able to ping external world, but fail to ping host ip.
> > > * Why it is so ?*
> > > b. Host Machine not able to ping external world.
> > > *Why VM can excess external world, but host not ?*
> > >
> > >
> > > Thanks & Regards
> > > Ashish
> > >
> > >
>
> > _______________________________________________
> > discuss mailing list
> > discuss at openvswitch.org
> > http://openvswitch.org/mailman/listinfo/discuss
>
>
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