Ethernet Switching Guide

02 /Contents

• 01VLANs: Broadcast Domains, 802.1Q Tagging and Trunk PortsGuide

  A VLAN splits one physical switch into several broadcast domains. 802.1Q tags carry those domains across shared links, and a router or Layer 3 switch joins them back together on purpose.

• 02Link Aggregation and LACP: Bundling Ethernet LinksGuide

  Link aggregation combines several physical Ethernet links into one logical link for more capacity and for survival when a member fails. LACP negotiates the bundle; hashing decides which member each flow uses.

• 03Spanning Tree Protocol: STP, RSTP and MSTP ExplainedGuide

  Spanning tree protocol keeps a switched Ethernet network loop-free by electing a root bridge and blocking redundant paths until a failure makes them necessary.

• 04802.1X Port Authentication: Supplicant, Authenticator, RADIUSGuide

  802.1X stops a switch port from forwarding until the attached device proves who it is. The switch relays EAP messages to a RADIUS server and applies the VLAN or policy the server returns.

• 05Layer 2 vs Layer 3 Switch: Where Each BelongsGuide

  A Layer 2 switch forwards frames by MAC address inside one VLAN. A Layer 3 switch also routes packets between VLANs in hardware. The choice is about where the device sits and what has to cross it.

• 06Power over Ethernet: 802.3af, 802.3at and 802.3bt BudgetsGuide

  Power over Ethernet delivers DC power and data over the same twisted-pair cable so phones, access points and cameras need no local mains. The switch power budget, not the port count, decides how many you can run.

02.1 /Orientation

An Ethernet switch forwards frames by MAC address, learns where addresses live by watching source fields, and floods what it does not know. Everything else in switching is a control mechanism layered on that behaviour: VLANs split one switch into several broadcast domains, trunks carry many VLANs over one link, link aggregation makes several links behave as one, spanning tree stops redundant links from becoming loops, and 802.1X decides whether a port should forward anything at all. A Layer 3 switch adds routing between VLANs in the same hardware.

The guides follow that stack. VLANs covers 802.1Q tagging, access and trunk ports, native VLAN pitfalls and inter-VLAN routing. Link aggregation explains static bundles and LACP, why a single flow never exceeds one member link, and the mismatches that keep a bundle down. Spanning tree walks through root election, RSTP convergence and the guards that protect an access layer. 802.1X covers supplicant, authenticator and RADIUS server roles, MAC authentication bypass and dynamic VLANs. Layer 2 versus Layer 3 is the buying and design decision, and Power over Ethernet is the budget arithmetic behind phones and access points.

Foundry's product map used exactly this split: Layer 2/3 wiring-closet switches (FastIron, EdgeIron) and Layer 3 backbone switches (BigIron). The IronWare command line built VLANs from port membership and called link aggregation trunking, and its configuration guide chapters on VLANs, trunking and port monitoring were among the most externally linked pages on the original site. Those chapters are the recovered documents in the margin. The profiles for FastIron, BigIron and EdgeIron live in the archive.

The recurring lesson across the section is that switching failures are configuration mismatches between two ends of a link: a native VLAN that differs, a member port at the wrong speed, a spanning tree root that was never set deliberately, a RADIUS attribute the switch does not understand. Every guide therefore ends with the show commands that expose the mismatch, because knowing where to look is most of the fix.

Nothing here requires Foundry hardware. The 802.1Q, 802.1AX, 802.1D/w/s, 802.1X and 802.3af/at/bt standards are the same on every vendor's switch; the IronWare examples are one accent, not the subject.