• Author : Ritika Adlakha


Troubleshooting STP instability 

Spanning Tree Protocol  A Layer 2 network protocol that ensures a loop-free topology for any bridged Ethernet LAN. The Spanning tree protocol allows the network to include redundant links as automatic backup paths that are available when an active link fails without creating loops or requiring manual intervention. The original STP is standardized as IEEE 802.1D. There are several variations to the original STP to improve performance and add capacity. Arista switches support these STP versions: Rapid Spanning Tree  (RSTP 802.1w) Rapid Per-VLAN Spanning Tree (Rapid-PVST) Multiple Spanning Tree (MSTP 802.1s)  Objective  In L2 networks, there can be physical layer...
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PVST BPDUs as data plane for MST

Introduction Arista Switches support the leading spanning tree protocols: RSTP, MSTP, and Rapid-PVST. Multiple Spanning Tree Protocol (MSTP/802.1s) is used by default. However, Rapid Spanning Tree Protocol (RSTP/802.1w), as well as Rapid Per-VLAN Spanning Tree (Rapid-PVST) are configurable. Objective This article is to provide an understanding of how PVST BPDUs are processed on Arista switches running MSTP. PVST BPDUs in MST Region In the case of Rapid PVST To interact properly with the Common Spanning Tree (CST), IEEE BPDUs are sent untagged to the reserved multicast MAC address of 0180.c200.0000. These BPDUs are generated and processed in VLAN 1 irrespective...
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Tap aggregation QoS handling on tap ports

This article describes how QoS attributes are handled on tap ports as of EOS 4.20.5F. Prior to EOS 4.20.5F, QoS behavior was not enforced for tap aggregation ports, meaning that QoS behaviour for packets passing through the device were not changed. Platform compatibility DCS-7280E DCS-7280R DCS-7500E DCS-7500R DCS-7280R2 Note: QoS is not available on Tap aggregation ports on the DCS-7150. Configuration Trust mode of tap ports Tap ports are put in ‘no qos trust’ mode by default. This means that the QoS marking of an incoming packet is not trusted when determining the QoS attributes of the packet. Therefore the...
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