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2003 Survivor's Guide to Infrastructure: Page 9 of 22

If you feel you need 10 Gigabit, consider restricting your purchase to products that support Xenpak interfaces. Xenpak cartridges are equivalent to the GBICs (gigabit interface converters) used for gigabit connections and will let you easily change out the four different types of optics defined for 10 Gigabit as needed. But beware of vendors that will support only their Xenpaks, as such practices defeat the purpose. Third-party Xenpack suppliers will drive down the price per port of 10 Gigabit and some vendors are understandably not excited about that.

Although no vendors have announced plans to upgrade their backbone chassis, it's probably just a matter of time. If you're going to do a major backbone upgrade, you need to know how old a vendor's current technology is and when its next-generation product is shipping.

Network equipment is not only getting cheaper, it's getting smarter. Most routers and switches now let you look deep into the contents of a packet and decide what to do with it depending on what is found.

Many switches that normally operate at Layer 2 now let you add security filtering at Layer 3. This means you can get tighter control over who has access to what within your organization. And packets can be prioritized by IP address, port combinations and DiffServ (Differentiated Services) code points. Many products accomplish this using ASICs that maintain true wire-speed performance.

As for Layer 2 QoS, look for products that support the 802.1p standard. And if you have a routed backbone, make sure it can carry Layer 2 QoS from end to end. When you consider that a router puts a new frame on every packet, any Layer 2 QoS is lost unless a translation takes place as it goes in and out of the router. This is especially critical for latency-sensitive applications like VoIP (voice over IP). If a VoIP packet is marked with Layer 2 and Layer 3 QoS, as many IP phones do by the time the packet gets into a Layer 2 network on the other side of the router, it will be on its own unless the core router rewrites the outgoing frame with Layer 2 QoS. You also want to be able to enforce your QoS policies at the core--the core router should be able to rewrite the QoS attributes in a packet based on your policies so that you are not at the mercy of the end stations.

The biggest problem you will encounter is configuring and managing it all. The implementation of many of these features usually requires the use of cryptic commands at the command line. If you have a larger network, you could end up with a poorly documented mishmash of ACLs. A good GUI-based configuration-management application can go a long way toward addressing this problem. Look for vendors whose products come with GUI interfaces that let you quickly and easily program end-to-end QoS.