Wide Area 'LANs'

We can all agree that a LAN is a locally connected network. Today, we probably access a network using a home wireless router. In the mid to late 90's, however, LANs were typically long runs of coaxial copper, segmented by Network Attachment Points (50 Ohm t-pieces, etc.).

Luckily, modern protocols and the modern equivalent of "just throw more resources at it" for encapsulation let us recreate that LAN over the widest area network we call the Internet.

LAN extension is not a new thing, and it's not a typical default design choice — it is a functional trade-off. When used appropriately, it enables capabilities that are difficult or impossible to achieve with pure Layer 3 routing and plays really well for our retro community for protocols that run on Ethernet.

• Preserving legacy protocols that rely on broadcast or non-routable addressing
• Stretching VLANs between sites for clustering, HA pairs, or migration
• Supporting non-IP traffic or tightly coupled systems
• Simplifying endpoint configuration where re-addressing is impractical

At the same time, we will introduce operational risks, including broadcast amplification, failure-domain expansion, and more complex troubleshooting. For this reason, modern designs aim to limit scope, control flooding, and encapsulate only what is necessary.

If we do this, and we should do this, then we all need to be good citizens.