Nortel’s BayStack 5520 stackable switch offers better performance, increased link aggregation capacity, new Layer 3 forwarding and a 25% price drop compared with its predecessor. However, this line of switches still has no routing protocol support and some management quirks that could detract from its overall usefulness.
Nortel’s BayStack 5520 stackable switch offers better performance, increased link aggregation capacity, new Layer 3 forwarding and a 25% price drop compared with its predecessor (see here). However, this line of switches still has no routing protocol support and some management quirks that could detract from its overall usefulness.
How we did it
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A single 5520 has 48 copper 10/100/1000M bit/sec ports and four small form-factor pluggable ports. The backplane supports up to eight switches in a stack with 40G bit/sec throughput into and out of each switch. The performance of both a single switch and a three-switch stack was acceptable, but not exceptional. (See How we did it .)
There was line rate performance at Layer 2 with a single switch with all packet sizes. But performance degraded somewhat as the packet size increased with Layer 3 switching. Here we saw line rate throughput for 64- to 512-byte packets, but throughput decreased to 82% of line rate as the packet size increased to 1,518 bytes.
Latency values for a single switch ranged from about 10 microsec in the best case (with 64-byte packets) to 200 microsec (with 1,518-byte packets) when the switch was near full capacity. This is most likely because of the increased overhead of the internal chipset that chops packets into smaller units and then switches them across the backplane.
With three switches, we pumped as much as 130G bit/sec (64-byte packets) and as little as 72G bit/sec (1,518-byte packets) through the stack in a full mesh configuration. Layer 3 forwarding performance decreased as the packet size increased, as well. This amount of stack bandwidth should be adequate for most enterprise network applications with the exception of a highly utilized core network. Latency measurements for the stack were similar to the single switch test results.
The benefit of Layer 3 switching – in spite of the slight performance hit – is that it allows an administrator to configure an IP subnet for each port and/or virtual LAN (VLAN ) in the switch. This is a great way to segregate network devices and minimize Ethernet broadcast traffic, but the only way to let the stack or other network devices know that other subnets exist is by configuring static routes. This can quickly become an administrative nightmare. Therefore, Layer 3 switching is best used when most routes are contiguous and can be summarized by a few addresses. Routing protocol support (which Nortel says is coming, but won’t say when) would relieve this limitation.
The reboot times for the 5520 in stand-alone and stack configuration is acceptable at less than 90 seconds.
The 5520 has a rich set of QoS features such as 802.1p VLAN tagging priority and Differentiated Services . Each port can have as many as eight egress queues. The number of queues per port is configured globally, which requires a reboot. We tested 802.1p priority queuing on both a single switch and a three-switch stack. It prioritized both packet loss and latency of the various tagged flows through the switches.
Link aggregation capabilities have been expanded so that all ports can be added to a link aggregation group. However, only four ports can be active at any one time. If more than four ports are added, the first four ports are active and the remaining ports are on standby. If an active port goes down, one of the standby ports becomes active. The switch is capable of supporting 4G bit/sec throughput through one group. Multiple groups can be configured on the switch. Nortel also has implemented the link aggregation control protocol standard to automatically configure link aggregation groups.
The 5520 offers a wide array of management capabilities. The Web interface allows for remote configuration of the stack. It’s similar to previous Nortel Web GUIs, with the addition of a few configuration options for the new 5520 features. Unfortunately, Nortel did not include a way to configure IP for individual VLANs through the Web interface. This is a basic configuration option for Layer 3 switches.
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The serial interface starts with a menu that allows an administrator to set up and view several categories of configurations. One of the menu choices gives access to a command-line interface (CLI), a Cisco-like command line that gives access to all the configuration options we could want. When the units are in a stack configuration, the CLIs of each unit in the stack are compiled into one CLI, accessible through the console port of any unit in the stack.
New to this release is a way to transfer the configuration files outside the switch via TFTP in ASCII format. This gives administrators the ability to view and change the ASCII configuration file on a desktop using a scripting language and then transfer the new configuration to the stack.
Device Manager (Version 5.8.7.0) was included with the switch we received for testing. It is an SNMP-based, Java application that we installed on a PC running Windows XP. This is a well thought out application that allows an administrator to change the configuration of a stack. There is no provision for managing multiple stacks except by running additional instances of the application, though.
Nortel has done a good job improving its stackable switch product line with Layer 3 switching capabilities. With its high bandwidth stack architecture, low per-port price point (about $110 per port), high port density, and the promise of routing protocol support, the BayStack 5520 is an attractive offering for most enterprise applications.
Bass is a senior technical staff member at North Carolina State University’s Centennial Networking Labs (CNL) in Raleigh. CNL tests network equipment and network-attached devices for interoperability and performance. Bass is co-author of Building Cisco Multilayer Switched Networks, and designs and leads the execution of the test suites. He can be reached at john_bass@ncsu.edu. Chintan Desai and Nader Shinouda of CNL assisted with the testing.
Bass is also a member of the Network World Lab Alliance, a cooperative of the premier reviewers in the network industry, each bringing to bear years of practical experience on every review. For more Lab Alliance information, including what it takes to become a member, go to www.networkworld.com/alliance.
