Inter-VLAN Routing — SVI & Router-on-a-Stick

Two ways to route between VLANs. SVI on a Layer 3 switch ip routing interface vlan 10 ip address 10.10.10.1 255.255.255.0 One SVI per routed VLAN; routing happens in hardware. Note: a L2 switch SVI is management-only (SSH, SNMP) plus ip default-gateway for the switch itself — it never routes user traffic. Router-on-a-stick interface g0/0.10 […]

802.1Q Trunking

802.1Q trunks carry multiple VLANs on one link by tagging each frame (12-bit VID); frames for the native VLAN stay untagged. A trunk with no allowed list passes every VLAN. interface Gi0/1 switchport mode trunk switchport trunk native vlan 99 switchport trunk allowed vlan 10,20,30 switchport nonegotiate ! silence DTP (security best practice) Mismatch failures […]

VLANs & the VLAN 1 Problem

A VLAN is a separate Layer 2 broadcast domain on shared switches. Hosts in the same VLAN talk directly; between VLANs you need routing (SVI or router-on-a-stick). VLAN IDs 1–4094; access port = one VLAN, trunk = many. VLAN 1 — the one Cisco tells you to avoid VLAN 1 is the default access and […]