QoS - more
Once bandwidth has been allocated to specific flows, traffic queue weighting can be enabled based on the CoS or DSCP markings. Traffic queuing occurs when there are bursts or extended amounts of traffic exceeding the router's throughput. This excess traffic is then held in buffers (queues) until it can be sent, or dropped if the buffer is full. Weighting options then come into play by determining which buffers/queues get to transmit packets first.
Enabling QoS by selecting Basic in the QoS mode and defining which markings are trusted on which ports allows the router to apply traffic weighting. The options are to trust the CoS or DSCP markings received from various ports, or overwrite them and assign a default value on untrusted ports.
The RVL has default mappings of CoS and DSCP values to Queues 1,2,3,4 based on standard QoS priorities, which can be adjusted. CoS values 0-7 can be mapped to Queues 1-4 as desired. DSCP values 0-63 can also be mapped to Queues 1-4 as desired. In most cases, the defaults should be fine.
There are also options to select whether Queues 1-4 are serviced using Strict Prioritization or Weighted Round Robin (WRR). Strict Prioritization means traffic in Queue 4 will be sent before traffic in Queue 3, which will be sent before traffic in Queue 2, leaving traffic in Queue 1 to be sent last. WRR will service all Queues in a weighted manner, allocating 53%-27%-13%-7% of transmission capability to Queues 4-3-2-1, respectively. Strict Prioritization is useful when there is traffic on the network where queuing delay or packet loss is absolutely unacceptable. The advantage of WRR is it allows for prioritizing sensitive traffic without starving lower priority flows, a condition that can occur in Strict Prioritization.
The bottom line is the Linksys RVL200 has the ability to manage traffic at very granular levels, which is a good thing. I just wish the QoS menus were a little easier to use. It seems the menu jumps from high-level options to low-level options and back, making it challenging to properly configure.
Dynamic DNS is very useful for WAN links with dynamic IP addresses. I find using Dynamic DNS simplifies VPN connections. Many routers support Dynamic DNS; I mention it here as the RVL200 supports only DynDNS.org for automatically updating a Domain to a dynamic IP address.
A useful troubleshooting tool on the RVL is the Port Mirroring feature. The feature creates a virtual hub, so to speak, by allowing a device on one port to capture packets being sent or received on another port.
For example, in Figure 10, I've configured the RVL200 to mirror packets from port 1 to port 2. With my laptop connected to port 2 and using a packet capture software tool like Wireshark, I can now run packet traces on all traffic going through port 1.
Figure 10: Configuring port mirroring
The RVL also supports SNMP v1-v3 network monitoring, which can be useful for collecting performance statistics and network alarm information. If used as a satellite office router, the RVL200 can be added to your network SNMP monitoring system at the home office.
From a performance standpoint, the RVL200's network throughput is steady. As shown in the IxChariot plot in Figure 11, throughput is pretty level for both WAN>LAN and LAN>WAN, producing a total average throughput of nearly 39 Mbps, without any significant peaks or drop-offs.
In comparison, we measured descending throughput levels and a cyclical WAN>LAN throughput pattern on the RV042 (see slideshow). In addition, our experience with the RVS4000 (see review) throughput was very unbalanced, with an extremely high upload capability of 516Mbps, but only 14Mbps download. This makes the RVL200 the most well behaved of these three Linksys products in terms of network throughput.