[CentOS] Centos box and Cisco 3750 VLAN's

[Blake Hudson]

Boris, I'd suggest reviewing the guide from Redhat on configuring your 
server 
(https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/s2-networkscripts-interfaces_802.1q-vlan-tagging.html)

In essence, eth0 is a shell. eth0.x is where all the traffic happens. 
VLANs will need to be explicitly defined on both the server and the 
switch in order for traffic to pass. Again, follow the RedHat guide for 
the server configuration. Be sure to set the interface filename and the 
device name inside the file to match the VLAN ID you're using. For 
example, VLAN 1 will be /etc/sysconfig/network-scripts/ifcfg-eth0.1 and 
the first line of the file should be DEVICE=eth0.1. VLAN 2 should use 
ifcfg-eth0.2 and DEVICE=eth0.2. It's easy to forget to update the DEVICE 
field inside the file and conflict with another device on the system so 
double check all work.

On the Cisco switch, define the VLANs:
> Switch# configure terminal
> Switch(config)# vlan 2
> Switch(config-vlan)# name vlan2
> Switch(config-vlan)# end
... repeat for each VLAN


And configure the ports:
> Switch# configure terminal
> Enter configuration commands, one per line.  End with CNTL/Z.
> Switch(config)# interface gigabitethernet0/1
> Switch(config-if)# switchport mode trunk
> Switch(config-if)# switchport trunk allowed vlan 1-4
> Switch(config-if)# end 
... repeat for other trunk ports. I'd also recommend turning off VTP and 
setting all non-trunk ports to access mode 
(http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swvlan.html#wp1150876).

--Blake






Boris Epstein wrote the following on 5/30/2014 2:59 PM:
> Hello all,
>
> I have a CentOS box that has a NIC (eth0) on which I defined 4 VLAN's
> (counting the NIC itself): eth0, eth0.1, eth0.2 and eht0.3. Initially the
> Cisco switch was not partitioned into VLAN's which means that the only VLAN
> running on it was the default one (VLAN 1).
>
> I have then played with VLAN's a bit on the switch and at this point have
> two: VLAN 1 (which is default and can not be deleted) and VLAN 3. The
> CentOS box is plugged into a trunk port on VLAN 3 which by virtue of being
> a trunk should belong to all VLANs. However, this does not seem to work as
> expected.
>
> What I get is the following:
>
> 1) eht0 does not come up at all.
>
> ifup eth0
> Device eth0 does not seem to be present, delaying initialization
>
> 2) eth0.3 comes up fine.
>
> 3) Other VLAN's do not come up. No error messages, just never show up.
>
> Any insight into this would be most welcome. Primarily, I fail to
> understand why all those VLAN's came up on VLAN 1 and why now even VLAN 1
> does not come up - even though the trunk port the device is plugged into is
> supposed to be a member of all VLAN's.
>
> Thanks in advance.
>
> Boris.
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