ImageStreams' TransPort Linux Router

Real-World Setup

ImageStream shipped the TransPort TR1000-TE to the Cal Poly Network Performance Research Lab so we could put it through its paces. In addition to the standard Ethernet ports, the TransPort TR1000-TE comes with a T1 link for a WAN (see "TransPort as Gateway," below), which we connected to one of the lab's edge routers to provide an outgoing connection to the campus backbone. We used one of the LAN interfaces to support a local subnet, including Web and e-mail servers. We configured NAT and port forwarding to support the server and the clients on the internal subnet.

The ImageStream Web site provides a thorough manual that walks you through the device's initial configuration. You set up global parameters--passwords, device name and DNS settings--via a menu interface. You then configure LAN and WAN port IP addresses and options like duplex, clocking and link speed by editing a configuration file. After entering only the IP information, we were pleased to see the T1 link connected to our edge router using the default settings.

Setting up the firewall options is much more difficult. If you don't know how to create Linux IPTable rule sets, plan on making full use of ImageStream's customer support. The company guarantees 24-hour turnaround time on translating Cisco ACLs (access-control lists) into IPTable rule sets. We used this option and received the rule set the next day. The lack of a Web interface for configuring firewall rules is a major drawback for a device aimed at smaller organizations. I brought this up with ImageStream and was told a Web interface is in the works for later this year.

For our LAN clients, we wanted to use DHCP for client network configuration, but the software isn't shipped with the product; however, ImageStream will provide it to you free upon request. Overall, the router worked as expected on our LAN.Performance Testing

The TransPort does all of its routing in software, so we had some concerns about throughput and latency. We ran our tests using Ixia Communications' 1600T traffic generator with IxExplorer software. The TransPort easily achieved line speed--1.5 Mbps--for large and small packet sizes on the T1 WAN interface.

The device also produced impressive numbers over its LAN links: For large packets, the TransPort achieved speeds greater than 92 Mbps. TransPort's throughput for very small packets decreased significantly, to 15 Mbps, a result you would expect for a software-based router. We then reran the same tests, this time with the device's firewall configured with 100 rules, and we saw only a slight drop in overall throughput--2 percent to 4 percent, depending on packet size.

We noticed a significant amount of variability in the TransPort's latency as it approached maximum throughput for a particular packet size, so we ran our latency tests using only 90 percent of this rate. The worst-case latency was 396 microseconds and only 455 microseconds when the firewall was configured with 100 rules--impressive!The TransPort has competitive throughput and latency numbers, and it supports a wide range of services. The device's configuration is menu-driven and does not hide the underlying Linux implementation from the user, which could be a problem for those with limited IT support or for those accustomed to an easier interface.

Hugh Smith is an assistant professor at the California Polytechnic State University in San Luis Obispo and a member of the Cal Poly Network Performance Research Lab. Students Scott Thomas and Brett Tsudama are members of the Cal Poly NetPRL. Write to them at [email protected].

Post a comment or question on this story.