Extreme Networks Alpine 3808: Broadband Access for MANs
Jun. 13, 2000 (Network Computing - CMP via COMTEX) -- The Alpine 3808 is the
latest and greatest switching platform from Extreme Networks. More than just a
new architecture, the Alpine switching family also ushers in a broadened market
focus for the vendor of purple wares.
The Alpine 3804 and 3808 are based on the same switching architecture as that of
the Extreme Summit 7i (see "With Its Summit 7i, Extreme Networks Climbs to New
Heights," at www.networkcomputing. com/1102/1102sp1.html). Just like the Summit
7i, the Alpine 3808 features a 32-Gbps nonblocking switch fabric. But unlike the
Summit 7i, which is a fixed-configuration switch, the Alpine 3808 has a modular,
chassis-based architecture.
The Alpine is Extreme's first foray into the modular wiring-closet switching
market. With a height of 14U (21 inches), the unit stands about as tall as a
Cisco Systems Catalyst 6500. Alpine's modular architecture has room for two
power supplies, one switch processor and up to eight expansion cards. The Alpine
switch has the same switching capacity and port density as Extreme's
BlackDiamond 6808 backbone switch but is only two-thirds the height.
I tested an early beta of the Alpine 3808. Using test equipment from IXIA
Communications, I benchmarked the Alpine 3808's throughput for packet sizes of
64 bytes, 1,024 bytes and 1,518 bytes on 32 1000BASE-SX Gigabit Ethernet ports.
Using a fully meshed traffic pattern, the switch forwarded all packets at Layer
2 and Layer 3 wire speed-a total throughput of 32 Gbps, or 48 million packets
per second.
I also stressed the Alpine 3808's IP QoS (Quality of Service) mechanism. The
Alpine 3808 has eight hardware-based queues per port and supports QoS via 802.1p
or IP DiffServ tags. Using the IXIA 1600 traffic generator, I set up eight
wire-speed gigabit flows all targeted at a single output port. Each flow was
given a different IP DiffServ code-point value that mapped into one of the
Alpine's eight hardware queues. Even with all eight ports running at wire speed,
the Alpine experienced no degradation of high-priority traffic.
Several new features have been added to the ExtremeWare 6.1 software, which runs
the Alpine 3808 as well as Extreme's other switches. These changes are part of
Extreme's new strategy to enter the switched gigabit MAN (metropolitan area
network) market. They include support for bidirectional port-based rate limiting
and counters that will eventually support usage-based billing.
A New MAN in Town
Another new feature is virtual MANs, or vMANs, as Extreme is calling them.
Similar to a VLAN (virtual LAN) but designed for the service provider, a vMAN
does a double encapsulation of Ethernet traffic, letting users run Layer 2
protocols inside an IP-based VLAN. This lets a customer link several buildings
serviced by the same service provider into a Layer 2 MAN. Protocols such as SNA
and DECnet can then be run inside a switched IP network. Likewise, the customer
can pass multiple VLANs using 802.1q tags because the traffic is encapsulated
again at the service-provider border gateway.
I tested Extreme's rate-limiting feature using a 10/100 module in the Alpine
3808 switch. I began by setting up bidirectional wire-speed flows between two
ports. Then, monitoring the throughput between the two ports, I applied changes
to the switch to enable rate limiting. Rate limiting can be controlled
independently in each direction. I found that while the rate limiting worked as
advertised, it wasn't very granular or consistent. I noticed significant
deviation from the programmed rate for smaller packet sizes; usually, the switch
overshot our expectations by 5 percent to 7 percent. Extreme engineers explained
that the current implementation was granular only to 16 fixed rates. These rates
are adjustable in the switch operating code, but the rates are not now
accessible by the end user. Larger packets exhibited far less deviation,
typically 1 percent or less.
The Balancing Act
Also new to the Alpine (and other Extreme i-series switches) is a wire-speed
server load-balancing mode. This is Extreme's first foray into the server
load-balancing market. The software I tested, called "go-go mode," is designed
to server load-balance only static Web content. It has no support for cookies or
persistent connections. Using a new set of benchmarks from IXIA software, I was
able to show that the Extreme "go-go" server load-balancing was able to sustain
16 million open sessions and handle wire-speed HTTP requests and ACKs.
To accomplish this server load-balancing, you need to set the MAC (Media Access
Control) address of all your servers to the same physical address. Thus, if you
want to do interserver communication, you need to install a second NIC in each
server and build an out-of-band network to handle that communication.
Furthermore, the current code doesn't really have any health checking built in,
so if a server goes down, you'll end up black-holing a significant fraction of
your user traffic. At the time of my tests, Extreme said it was developing a
server health-check mechanism for the release version of the code (available
now).
The feature list of the Alpine 3808 goes on and on. Extreme is also delivering a
feature called IP-TDM (IP time-division multiplexing). Not a revo- lution but a
new packet-scheduling algorithm, IP-TDM lets the Extreme Alpine guarantee
latency for small packet sizes.
The Alpine 3808 (including chassis, fan tray and power supply) lists for $29,980
with a switch processor module installed. The price-density curve dips as low as
$1,936 per 1000BASE-SX gigabit port in a fully loaded 32-port configuration.
Extreme is also shipping 100BASE-FX, 1000BASE-T and, next year, a 10-Gbps DWDM
(dense wave-division multiplexing) unit.
Send your comments on this article to Joel Conover at jconover@nwc.com.
Vendor Information
Alpine 3808, $29,980 with a switch processor module. Available: Now. Extreme
Networks, (888) 257-3000; fax (408) 579-3000. www.extremenetworks.com
nwc.com
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By: Joel Conover
Copyright 2000 CMP Media Inc.
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