Network Computingwww.networkcomputing.com

The DES-5024 offers VLAN (virtual LAN) configuration, port-trunking (bandwidth aggregation) and support for the Spanning Tree Protocol, SNMP and RMON. D-Link implements VLANs in this switch in a unique fashion: It permits cross-VLAN communication, giving you greater flexibility in your network designs. The switch also offers port-trunking--using a proprietary technology--which lets you bind up to eight connections to aggregate bandwidth to another switch. However, with only one unit in the lab, I wasn't able to test this feature.

The DES-5024 is easy to manage, making use of SNMP MIBs and four RMON groups (Statistics, History, Alarm and Host) for analysis, and telnet and serial connections for configuration. D-Link says it plans to include support for additional RMON groups in a future version. I encountered no problems with the console configuration, thanks to the straightforward documentation.

Renegade VLAN Tactics While D-Link's approach to implementing VLANs in this switch is out of the ordinary, once VLANs are configured on the switch, they operate just as you'd expect they would--by segmenting the broadcast traffic and preventing the VLANs from seeing traffic that does not belong to them. However, if there is a specific station in another VLAN that you are trying to communicate with, the switch will let this traffic cross the VLANs.

To test this fascinating implementation of VLANs, I configured two separate VLANs, placing two client computers on each VLAN and initiating a file transfer between them. With a network analyzer on one VLAN, I was unable to see the stations on the other VLAN. The switch deliberately prevents broadcast and other traffic from crossing VLANs. However, when the client on VLAN 1 communicated directly with the client on VLAN 2, the switch fostered this type of communication, alleviating the need for an extra router connection.

Consequently, the file transmission occurred between VLANs, and I was able to see the communication that was occurring between the different VLANs on the analyzer station.

In order to gauge its switching mettle, I tested the switch's performance with several Netcom Smartbits-based tests, including throughput, latency, packet loss and rapid back-to-back packet transmission. The DES-5024 easily handled 24 streams of Fast Ethernet traffic when the packet sizes were large, switching the traffic at wire speed. When the packet sizes were smaller, however, the switch experienced some problems and began dropping packets. I saw this undesirable behavior with 512-byte and smaller packets.

The DES-5024 is the sister switch of D-Link's DES-5016, but offers 24 (instead of 16) UTP ports. This 10/100 autonegotiating switch also has two expansion slots. (These two slots accommodate a 100BASE-FX uplink, an ATM uplink and a Gigabit Ethernet module for connection to your high-speed backbone.) Unfortunately, to reduce the cost of the switch, the DES-5024 makes use of the same switching fabric as the DES-5016. This saturates the switching engine with four more ports per card--but without any new electronics.

The DES-5024 is a modular, slotted chassis design, letting you interchange the expansion cards. To my disappointment, it does not offer other alternatives to the 12-port 10/100 cards and the modules are not hot-swappable. The DES-5016 offers 8-port 100BASE-FX cards in lieu of the 10/100 UTP cards, but the DES-5024 does not offer such options.

Mark Degner is a systems consultant for Entex Information Services. Send your comments on this article to him at mark.degner@entex.com.