Are VLANs on the comeback trail?

By Jeff Caruso
Network World, 10/25/99

After stumbling out of the limelight a few years ago, virtual LANs may be poised for a comeback, thanks to the efforts of two standards bodies.

The IEEE has two projects under way: One that would standardize the practice of segmenting VLANs by protocol, and another that would make VLANs more resistant to failures. In addition, the Internet Engineering Task Force (IETF) is crafting a way for third-party software to manage multivendor VLANs.

The advancements - which build on the standardization of VLAN tagging in IEEE 802.1Q last year - are renewing interest in the technology, even if some analysts say Layer 3 switches do away with the need for VLANs. A recent Infonetics Research survey found that 46% of IT organizations plan to implement VLANs by November 2000. The number jumps to 60% for companies with more than 1,000 employees.

"[IEEE] 802.1Q definitely helped spur this growth," says Mike McCon-nell, director of LANs and network management at San Jose-based Infonetics. "We used to see a 'two-years-out' mentality, but end users are deploying now that the technology is maturing."

IEEE 802.1Q is even taking some of the steam out of ATM in the campus, according to Mike Myrick, manager of technology services at the University of Mississippi. One of ATM's strengths is support for VLANs, but now Ethernet easily fulfills that function.

IEEE 802.1Q specifies how VLANs can be created by grouping switch ports into virtual LANs, but vendors have also enabled customers to create VLANs based on the protocol - such as IP or IPX - being carried.

The problem is, protocol-based VLAN support is particular to each vendor. The IEEE is now trying to standardize the approach in an effort dubbed 802.1v. The 802.1v work has just begun, but the group hopes to make substantial progress by the middle of next year, says Andrew Smith, software architect at Extreme Networks and project editor of 802.1v.

Lockheed Martin uses proprietary protocol-based VLANs, mainly to send DECnet and IP traffic through the same switch port, while keeping the DECnet traffic logically separate, says Joe Anderson, lead member of the engineering staff. "DECnet is very broadcast-intensive," Anderson says. "Everybody on the IP subnet doesn't want to hear the DECnet traffic."

Because 802.1v is still in its infancy, protocol-based VLANs are still proprietary, but 802.1Q provides a way for the VLANs to connect. Lockheed Martin is using 802.1Q to create a trunk between proprietary VLANs supported by its Xylan and Hewlett-Packard switches.

Another extension under consideration is making spanning tree sensitive to VLANs, Extreme's Smith says. A project called 802.1s provides for a scenario in which a user could have two redundant paths, or spanning trees, through a network, each supporting several VLANs and using as much bandwidth as needed.

If one path failed, 802.1s would make it possible to easily shift all those VLANs to the surviving path. Smith says the technical details are complete, and 802.1s is undergoing a working-group ballot right now.

On the management side, the IETF in August published a proposed standard that spells out how management software can set up and manage VLANs on different vendors' equipment. Cabletron's Spectrum business unit, which focuses on network management, is championing RFC 2674.

But at this point, Cabletron is the only major vendor supporting the proposed standard in its switches. 3Com says it will support RFC 2674 in its CoreBuilder switches next year.

Extreme, even though it co-authored the document, wouldn't say when it will offer support. Nortel Networks says it is waiting for user demand for the support. And Cisco says it will wait until after the RFC reaches draft standard status, which is expected to happen next year.