Thank you everyone.
OK, the mystery deepens, I guess. The machine does need to support several
VLAN's, it is currently on a trunkport (8021q encapsulated), it made it
into the ARP table - which I specifically tested for by physically
unplugging the table, clearing the ARP table and plugging it back in.
The ARP table currently looks like this:
hq#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 192.168.48.100 0 0025.6440.0301 ARPA Vlan48
Internet 192.168.48.101 - 001b.906a.bcc4 ARPA Vlan48
Internet 192.168.48.1 0 0025.6440.063f ARPA Vlan48
Internet 192.168.2.52 0 0025.6440.0547 ARPA Vlan2
Internet 192.168.3.1 - 001b.906a.bcc2 ARPA Vlan3
Internet 192.168.2.1 - 001b.906a.bcc1 ARPA Vlan2
Internet 192.168.7.1 - 001b.906a.bcc3 ARPA Vlan7
hq#
The network config on the machine currently looks like this: it has nothing
assigned to eth0, eth0.48 = 192.168.48.100/24, eth0.49 = 192.168.49.100/24,
eth0.50 = 192.168.50.100/24.
And - even though the ARP table seems to be OK - there is no connectivity!
Boris.
On Sun, Jan 25, 2015 at 11:42 AM, Les Mikesell <lesmikesell@xxxxxxxxx>
wrote:
> On Sun, Jan 25, 2015 at 8:38 AM, Andrew Holway <andrew.holway@xxxxxxxxx>
> wrote:
> > 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.
> >
>
> Just to add to that - normally if a host only needs to be on one
> subnet you would use an access port on the switch to select a single
> vlan and deliver those packets untagged so the host does not need to
> care about tags or vlan numbers. And to that end, switches default
> to treating everything as access ports on native/untagged vlan 0
> unless configured otherwise. However, if the host needs interfaces
> on multiple subnets, you can do it on a single network connection by
> giving it a trunk connection from the switch and letting it split out
> the vlan interfaces internally.
>
> --
> Les Mikesell
> lesmikesell@xxxxxxxxx
> _______________________________________________
> CentOS mailing list
> CentOS@xxxxxxxxxx
> http://lists.centos.org/mailman/listinfo/centos
>
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