Sometimes when you have a subnet accessible from an interface that is not along the default gateway (such as a group of private routed subnets in 10.x.y.z), you need to add a manual route. Say for example vlan 2 is on 10.1.0.0/16 and has a router on 10.1.1.1 that also serves 10.2.0.0/16. You cant put a GATEWAY=10.1.1.1 in the ifcfg-eth0.2 file, since that will (potentially) override the GATEWAY setting in ifcfg-eth0 that reaches the Internet...
VLAN
What? As if you weren’t confused enough already, now let’s combine the two concepts and create a bridge across a VLAN. That would be a bridge between two ethernet interfaces, where one is a real ethernet card in the PC (or a wifi, or some other regular type of ethernet interface), and the other will be a VLAN interface. Why? Let’s say you have a piece of equipment which by itself doesn’t know how to talk VLAN -but you...
What is a VLAN? VLAN is short for Virtual LAN (where LAN is short for Local Area Network). The virtual lan is pretty much what is sounds like – a virtual seperate network, but across the same physical network. Confused? Okay, think of it like separate conference rooms. Some computers are plugged into conference room A and can chat, some into conference B and can chat, but A and B can’t hear each other. Now do this in the same room,...
What is a bridge? A bridge acts just like a having an ethernet switch connected across two ethernet cards (NIC). Packets can flow in any direction as needed, intelligently, based on what MAC addresses are present on each network. What that means is that packets will only be echoed (or bridged across) to the other interface when that destination MAC address is on network (this is the same functionality provided by an ethernet switch, rather than...
The configuration of VLANs under FC/RHEL/CentOS is something that I always end up looking in the “ifup” script and experimenting around with. This is made worse by there being two different conventions that can be used for the interface naming. Here’s how I set up VLANs. First of all, the base interface needs to be configured. Usually, it’s already got at least a stub file, which needs to be modified to have the following...