Inter-VLAN Routing
VLANs define separate broadcast domains and must be separate IP subnets. The only way to get traffic from one VLAN to another is to route between them Inter-Vlan Routing . Inter-VLAN communication occurs between broadcast domain via a Layer 3 device such as router.
All VLANs can be transported across a trunk link to be distributed by the neighbor device. With inter-VLAN routing functions, the router must know how to reach all VLANs being interconnected.
Each VLAN must have a separate connection on the router, and we must enable 802.1Q trunking on those connections. We had need at least a fastethernet port on the router.
To support 802.1Q trunking, we must subdivide the physical fastethernet interface of the router. A sub-interface is a virtual interface that is spawned from the physical interface.
VLANs define separate broadcast domains and must be separate IP subnets. The only way to get traffic from one VLAN to another is to route between them Inter-Vlan Routing . Inter-VLAN communication occurs between broadcast domain via a Layer 3 device such as router.
All VLANs can be transported across a trunk link to be distributed by the neighbor device. With inter-VLAN routing functions, the router must know how to reach all VLANs being interconnected.
Each VLAN must have a separate connection on the router, and we must enable 802.1Q trunking on those connections. We had need at least a fastethernet port on the router.
To support 802.1Q trunking, we must subdivide the physical fastethernet interface of the router. A sub-interface is a virtual interface that is spawned from the physical interface.
We can configure it to run 802.1Q, build a subinterface for each VLAN. We can give those sub-interfaces IP addresses in the appropriate subnets for each VLAN, and let the router route between the VLANs whose traffic is coming up that trunk link. A frame destined for VLAN 20 could come up the trunk link from VLAN 10 to the Router's VLAN 10 sub-interface, get routed to VLAN 20, and leave that same port from the VLAN 20 sub-interface. The hosts in each VLAN will use the sub-interface configured for their VLAN as their default gateway.
The configuration between a router and a core switch is sometimes referred to as a router on a stick. Following Figure illustrates a router attached to a core switch.
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