This tag is associated with 9 posts

Flow Control – Pause Frames

. When an Ethernet device gets over loaded, flow control allows it to send PAUSE requests to the  devices sending it data to allow the over loaded condition to clear.  If flow control is not enabled and an over loaded condition occurs, the device will drop packets. Dropping packets is much more performance impacting than flow control. 802.3X flow … Continue reading

Layer 2 Discards Troubleshooting – RX TX Discards

. The following list of questions/vectors can assist in troubleshooting Layer 2 discard issues. They have been of help to me in the past on more than one occasion. What Switches/Models? What firmware versions? Look at the subsequent firmwares’ release notes for any identified issues, resolved caveats etc. that match what you re experiencing. What … Continue reading

Switch Port auto shuts/ port shuts itself down – Troubleshooting

. Following is a list of vectors that may assist in troubleshooting issues where the port behavior look like it is shutting itself down. Cable/ Power Management. A link light does not guarantee that the cable is fully functional. The cable could have encountered physical stress that causes it to be functional at a marginal … Continue reading

Powerconnect SFP/Fiber connectivity – Options, Requirements and Troubleshooting

Basic requirements for fiber connections on PowerConnect switches: MMF optical cables, LC connectors, and SFP transceivers. 1)     Optical Cables :   Single Mode Vs Multi Mode Single Mode cable has a diameter of 8.3 to 10 microns, through which only one mode will propagate, typically 1310 or 1550nm. SMF gives you a higher transmission rate and up to … Continue reading

Latency, Packet loss Troubleshooting (PowerConnect, Others)

. First, know your network. know the topology. if you have a network in place where by design, the majority of the variables are deterministic & not left to chance, the task gets a lot simpler. with this out of the way, the following are the different outputs and avenues that might shed further light … Continue reading

Powerconnect Switches: Oversized Packet Counter, bcmRX task

. In a blade chassis implementation some time ago, some concerns were raised on the value of packet counters, and an inquiry on the bcmRX task. the notes i compiled as part of my reply, are as below: The Oversized Packets counter can be safely ignored, as it is not indicative of a problem. What … Continue reading

Powerconnect – Stacked Vs. Standalone Configuration

. A fairly common design choice to be faced with during deployments, is  whether to use Stacking, Standalone, or vPC/VLT (a dual control plane implementation of MLAG) model, in the different layers of the switching infrastructure. This post draws a comparison between Stacking and Standalone models. A different post draws the comparison between stacking and … Continue reading

PowerConnect Switchport modes

. This post gives a comparison between the different port modes available on the Dell PowerConnect switches. the trunk and access modes are familiar to anyone who understands tagged and untagged transmission, the general mode however allows a lot more flexibility with port configurations. Trunk: all packets transmitted are tagged.  Untagged received traffic is dropped.  Tagged received … Continue reading

Switch fabric setup for iSCSI

. This post summarizes various elements which, in my experience, serve to optimize the iSCSI switch fabric. While it talks about Powerconnect switches, the elements discussed would be relevant to any switch model, used in the particular role. . a)      Global : Arp cache-size 1024 mac address-table aging-time 1230 spanning-tree portfast bpdufilter default : discard … Continue reading