Category : Tech Tips

Objective This article is going to explain few important Copp queues of Arista Sand platforms- 7280 series, 7020 series, 7500 series that are responsible for handling various control-plane packets and how to troubleshoot based on that.  Copp or Control Plane Policing are various queues or buffers in Arista switches for handling various plane packets. Different Copp handles different kinds of control-plane packets and each has its own significance. The control plane policing (CoPP) feature increases security on the switch by protecting the CPU from unnecessary or DOS traffic and giving priority to important control plane traffic.. It also segregates different...
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This article covers some of the scenarios in which the switch will flood Unknown Unicast traffic.  Unknown unicast flooding is observed when traffic received is destined to MAC addresses not learned on the switch. Since MAC addresses are usually learned from the source MAC for the host, switches could either : Never learn the MAC address if we never receive a packet with that source MAC address Time out such MAC addresses if we do not receive traffic with that source MAC for a duration greater than the MAC address timeout interval. Flush MAC addresses on receiving an STP TCN...
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Overview This document aims at providing the basic steps to follow for troubleshooting LACP related issues. Introduction The Link Aggregation Control Protocol (LACP), described by IEEE 802.3ad, defines a method for two devices to establish and maintain link aggregation groups (LAGs). When LACP is enabled, our switch can configure LACP-compatible ports into a LAG (also called a channel group). Initial Checks 1. Interface status of the bundled interfaces Check if the physical interfaces configured to be a part of the port-channel are connected using the command show interfaces status. For the port-channel to be up, at least one member interface...
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What is Congestion Congestion happens when a device receives more traffic than it can buffer or send out of an egress port. Whenever the network is congested, we can observe symptoms such as packet loss, slowness, low throughput and high latency.   Expected Behavior of the switch When a switch receives a packet, it takes an action to either forward or drop it. If the switch decides to forward the packet, it stores this packet in its buffer, where this packet gets queued to be sent to the egress port. Eventually, this packet gets sent out of the egress port....
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Overview This article details the steps needed to install/uninstall patches on Arista devices. Installation Steps Check the hardware platform and the EOS version running on the device using the “show version” command: Switch#show version Arista DCS-7150S-52-CL-F Hardware version: 02.01 Software image version: 4.20.11M Architecture: i386 If specified, ensure the device to which the patch needs to be applied is running on a relevant EOS release and is of the relevant platform. Patch installation on single supervisor/fixed system switches Step1: Download the patch extension file (.rpm or .swix file) and copy it to the “flash:” (/mnt/flash) directory of the device using...
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Objective During the upgrade process, there could be multiple reasons for the switch to get stuck in Aboot such as corrupted image, unsupported image, incorrect boot file, or no image to boot from. The aim of this document is to describe the recovery procedure of the switch from Aboot shell.   Procedure Step1: Check if the relevant EOS image is already present in the /mnt/flash Aboot# cd /mnt/flash ← Change the directory to flash Aboot# ls ← list the contents of flash EOS-4.21.6F.swi  boot-extensions   persist scripts FSCK0000.REC   config_match rc.d  startup-config If the relevant EOS image is present, continue from...
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Description Time stamping is an important tool for network engineering and performance analysis. EOS-4.21.3F adds support for payload timestamping of all GRE encapsulated mirrored packets at line rate (only supported on the 7500R/7280R/7500R2/7280R2 series). A timestamp is taken on ingress and inserted into the GRE encapsulated mirrored packet payload at egress. More details about this feature can be found at https://eos.arista.com/eos-4-21-3f/mirroring-to-gre-timestamping This feature introduces an enhancement to Arista Timestamp Header Wireshark Dissector described in https://eos.arista.com/analyzing-packet-header-timestamps-in-wireshark/ How to Use All necessary steps on how to use new Wireshark Dissector described at https://github.com/mpergament/wireshark-arista-tagagg-dissector

Overview On a 7280 / 7500 devices, any known unicast packet which arrives on an ingress port is classified by the ingress processor based on priority level and egress port, and enqueued in the Virtual Output Queue (VOQ). The same would apply for BUM traffic if ingress only replication is enabled. The packet is enqueued on the ingress chip buffers until the egress packet scheduler issues a credit grant for the given packet. DeqDelete drops indicate stale packets in VOQ, i.e, packets which have been in the VOQ for more than 500ms without getting credits. These packets are deleted, and...
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Objective The aim of this document is to describe the procedure assisting in the physical replacement of one of the MLAG devices (for example in RMA scenarios where one device has a hardware fault and requires a replacement with a new one). Minimal traffic disruption during the time of this replacement is desired from an MLAG setup due to peer redundancy. It would not ensure zero loss as during the replacement, loss of in flight packets (going towards the switch being replaced) is inevitable. Introduction MLAG by Arista is a method to provide an active-active device level redundancy in the...
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Platform : 7050 Series,  7060, 7260 Series and 7304 Series. This document explains how to mitigate the output discards that are caused on the following platforms, due to congestion. How to determine if the drops are due to congestion : If the rate of traffic is nearing / exceeding the link bandwidth, it is pretty easy to understand that the drops are happening due to congestion. If the traffic rate is well within the interface bandwidth and still the drops are happening, they might be due to microbursts. ( Microbursts are huge spikes in traffic rate, which happen and end...
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Scope This article describes the “Best Master Clock Algorithm”(BMCA) and the manner in which it’s carried out on Arista switches. BMCA BMCA is used for selecting a Grandmaster (GM) in a PTP domain. Additionally, it is also used to decide the PTP port-states on the Arista switches. PTP port-states Master It provides timing to a downstream clock. PTP master ports send out announce messages. Slave It retrieves timing from an upstream clock. In this state, the port doesn’t send out announce messages. Passive A backup slave port. This state prevents timing loops. There are no announce messages sent out of...
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I. Overview The following article describes the functionality of routing context mode and how to use the functionality to export the logs and files from the device to the Desktop machine or to the backup/storage server. II. Introduction In most of the networking infrastructure, the networking devices are being administered or accessed in non-default vrf (Management VRF). The non-default will have access to the Network orchestration tools, Backup servers, Desktop machines depending upon the network infrastructure policy. Network Administrators / Orchestrators will use the Management vrf plane to communicate with the Networking devices.  The routing-context mode in EOS CLI makes...
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