On 25 January 2015 at 15:12, Boris Epstein <borepstein@xxxxxxxxx> wrote:
> OK... but why does it need to be a trunk port?
>
Because a trunk port will "trunk" the vlan.
A VLAN is basically a 4 byte "tag" that gets injected into the packet
header when the packet enters the VLAN network. When we trunk a VLAN we say
to the switch "pass packets on VLAN x but do not strip the tag out".
You can either terminate the VLAN at the switch port (untagged) which will
strip out the VLAN tag or you can pass the packet containing the VLAN tag
to the computer or other device(tagged/trunk). This device can then pull
out the tag. On linux this mechanism is done by an 8021q VLAN interface.
Hope this is useful.
ta
Andrew
>
> Boris.
>
> On Sat, Jan 24, 2015 at 6:53 PM, SilverTip257 <silvertip257@xxxxxxxxx>
> wrote:
>
> > Andrew and Dennis are spot on.
> > Their conclusions about your server being connected to an access port and
> > not a trunk port would be my conclusion as well.
> >
> > On Sat, Jan 24, 2015 at 9:11 AM, Dennis Jacobfeuerborn <
> > dennisml@xxxxxxxxxxxx> wrote:
> >
> > > Hi Boris,
> > > what I'd like to know is the actual VLAN configuration of the switch
> > > port (link-type and tagged and untagged VLANs). When I look at the
> > > switchport coniguration here I get (among other things):
> > >
> > > ...
> > > Port link-type: trunk
> > > Tagged VLAN ID : 8, 1624
> > > Untagged VLAN ID : 10
> > > ...
> > >
> > > Here is my suspicion:
> > > Your ports have an access link-type with an untagged VLAN ID of 48.
> That
> > > would explain why the moment you configure an IP from that VLAN on eth0
> > > you get connectivity because then the packets the Linux box sends are
> > > untagged as the switch would expect them to be. If you only put an
> > > address on eth0.48 then the packets get tagged by Linux but if the
> > > switch port is not configured to receive the packets for VLAN 48 as
> > > tagged then it will simply drop these packets and you will not get
> > > connectivity.
> > >
> >
> > Additionally, the switch should gripe about 802.1q BPDUs.
> > Check the in-memory system log (or syslog server if you have configured
> > that).
> >
> > show logging | i 1Q
> >
> > Example:
> > 1w1d: %SPANTREE-2-RECV_1Q_NON_TRUNK:
> > Received 802.1Q BPDU on non trunk FastEthernet0/2 on vlan 100.
> >
> >
> > >
> > > So getting the actual VLAN config of the switch port would help to
> > > determine if the switch actually expects to receive the packets the way
> > > you send them from the Linux box.
> > >
> > >
> > +1
> > Let's see the config for the switch port your server is connected to.
> >
> > --
> > ---~~.~~---
> > Mike
> > // SilverTip257 //
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