Cabling and Duplex
Using the appropriate cables and interface settings for in-path deployments are vital to performance and resiliency. The physical cabling and interface settings that connect the SteelHead to the LAN and WAN equipment (typically a switch and router) at the site must be correct. Duplex mismatches between the SteelHead and equipment connected to it, either during normal operations or during failures when the SteelHead is in fail-to-wire mode, have a significant impact on the performance of all traffic passing through the SteelHead. This section includes the following topics:
Choosing the Correct CablesDuplex ConfigurationTroubleshooting Cable and Duplex IssuesA duplex mismatch or incorrect interface settings might cause optimized performance to be less than nonoptimized performance or prevent traffic from flowing—even if the SteelHead is configured properly.
Choosing the Correct Cables
The LAN and WAN ports on the SteelHead bypass cards act like host interfaces during normal operation. During fail-to-wire mode, the LAN and WAN ports act as the ends of a crossover cable. Using the correct cable to connect these ports to other network equipment ensures proper operation during fail-to-wire mode and normal operating conditions.
Riverbed recommends that you do not rely on automatic MDI/MDI-X to automatically sense the cable type. The installation might work when the SteelHead is optimizing traffic, but it might not if the in-path bypass card transitions to fail-to-wire mode.
One way to help ensure that you use the correct cables during an installation is to connect the LAN and WAN interfaces of the SteelHead while the SteelHead is powered off. This proves that the devices either side of the SteelHead can communicate correctly without any errors or other problems.
In the most common in-path configuration, a SteelHead's LAN port is connected to a switch and the SteelHead's WAN port is connected to a router. In this configuration, a straight-through Ethernet cable can connect the SteelHead's LAN to the switch, and a crossover cable must be used to connect the SteelHead's WAN port to the router.
The following table summarizes the correct cable usage in the SteelHead.
Devices | Cable |
SteelHead or Interceptor to SteelHead or Interceptor | Crossover |
SteelHead or Interceptor to router | Crossover |
SteelHead or Interceptor to switch | Straight-through |
SteelHead or Interceptor to host | Crossover |
Duplex Configuration
Depending on which SteelHead bypass card you use, you must choose between manually setting the speed and duplex for its LAN and WAN interfaces or allowing the interfaces to automatically negotiate. Choosing the correct setting ensures that packets can pass through the interfaces, both during normal operating mode and during fail-to-wire mode, without any errors or drops due to a mismatch between the SteelHead and its connected network equipment.
The correct duplex settings to use depends on the capabilities of all of the interfaces in the chain of in-path interfaces: the connected LAN device (typically a switch), the LAN and WAN ports on the SteelHead bypass cards in use by one or more in-path SteelHeads, and the connected device (typically a router). A typical in-path deployment has a SteelHead LAN port connecting to a switch port that is 10/100/1000 Mbps capable, but the SteelHead WAN port connects to a router interface that is only capable of 10/100. In this deployment, manually set both the SteelHead LAN and WAN ports to use 100 Mbps, full duplex. This ensures correct operation during normal operation and fail-to-wire mode.
Riverbed recommends the following:
If all interfaces in the in-path chain are capable of 1 Gbps or higher speeds, use automatic negotiation on all interfaces in the in-path chain.Configure for automatic negotiation on all Ethernet ports running at 100 Mbps unless you know for sure of a specific automatic negotiation issue between the SteelHead port and the peer device.Never use half duplex—either set manually to full duplex or use automatic negotiation.If you deviate from these recommendations, you must perform tests to verify that traffic flows when the SteelHead is optimizing traffic and entered fail-to-wire mode.
For example, this can happen if the LAN interface is connected to a 1-Gbps device, and the WAN interface is connected to a 100-Mbps device, and WAN bandwidth close or equal to 100 Mbps. To avoid any potential bottleneck that prevents the SteelHead LAN interface from sending or receiving data at a rate greater than 100 Mbps, it is prudent for you to use automatic negotiation on both LAN and WAN interfaces. If you use automatic negotiation, the SteelHead can perform at its best both on the LAN side and the WAN side.
Duplex misconfiguration is not limited to the chain of in-path interfaces, especially at remote locations, where WAN limitations restrict the potential performance of applications. There might be long-standing, unrealized duplex-related errors in the existing LAN infrastructure, or even on host interfaces. You might only discover these long-standing issues when a SteelHead is deployed at the site and attention is concentrated on achieving high performance. Due to the infrastructure duplex problems, the SteelHead performance gains are not as significant as expected. Any such infrastructure issues limit the optimization possible by deploying a SteelHead, and must be resolved to realize the full benefits of a SteelHead deployment.
The following signs indicate a duplex misconfiguration:
You cannot connect to an attached device.You can connect to a device when you choose automatic negotiation, but you cannot connect to that same device when you manually set the speed or duplex.You detect performance issues across the network. Troubleshooting Cable and Duplex Issues
This section shows common cable and duplex troubleshooting procedures.
To verify if slow performance on the network is due to a duplex problem on the chain of in-path interfaces
From the Management Console, open Reports > Networking: Interface Counters.
Look for positive values for the following fields:
DiscardsErrorsOverrunsFrameCarrier countsCollisionsThese values are zero on a healthy network, unless you use half duplex. Riverbed recommends that you do not use half duplex.
To verify if slow performance on the network is due to a duplex problem within the LAN infrastructure, and not on an interface in the in-path chain
From the Management Console, open the Reports > Networking: Current Connections.
Look for any optimized connection, and click the magnifying glass icon next to the connection to see its details.
Look for zeroes in the following fields:
RetransmittedFast RetransmittedTime-outsIf the values are greater than zero, some type of LAN-side packet loss was experienced for that connection. This might be because of a duplex misconfiguration somewhere between the local host and the SteelHead's LAN interface.
Speed and duplex issues might be present at other points in the network path besides the interfaces directly connected to the SteelHead. There might be long-standing interface errors within the LAN, whose symptoms might have been incorrectly blamed on WAN performance.