• Category : Tech Tips

 
 

Resilient load-sharing using Nexthop Groups

Introduction Load-sharing of traffic flows towards a specific prefix in a L3 topology is usually achieved with Equal-Cost Multi-Path (ECMP) routing. With ECMP, multiple nexthops of equal preference are available for the prefix. Traffic is distributed towards the different next-hops based on a hashing algorithm and packets belonging to the same traffic flow are by default hashed to the same nexthop. A problem with ECMP is that if one of the nexthops is removed all flows are affected as a new hash should be calculated for all flows based on the remaining active nexthops. This can be remediated by using...
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Installing/Uninstalling a software patch on an Arista device

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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DHCP Server on Arista EOS

Overview In this document, a DHCP server will be installed on the switch, and configured to deliver IP addresses for a subnet/VLAN interface on the switch serving both IPv4 and IPv6 address families. All examples are demonstrated on Arista EOS release 4.20.7M. Install the DHCPD extension An extension is a Red Hat Linux .rpm file type or an archive of .rpm files in a .swi format. For this example the latest .swi package for DHCPD is downloaded from Arista repository to the switch and installed as a recognized extension. Download the extension: Please make sure you have reached out to Arista...
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SNMPv1/v2c Configuration

Objective The document is aimed to provide basic configuration needed on Arista switches to be able to monitor the device statistics using an SNMP monitoring tool. Configuration  Enable SNMP SNMPv1: The Simple Network Management Protocol, defined in RFC 1157. This version uses plaintext community name for interacting with the SNMP monitoring server. SNMPv2c: Community-string based Administrative Framework for SNMPv2, defined in RFC 1901, RFC 1905, and RFC 1906. This version also uses plaintext community string. Hence, the security level is the same as SNMPv1.  To query Arista switches using SNMP v1 or v2c, define a community name on the switch...
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Tap Aggregation PTP Sync & Transparent Clock (TC) PTP Multicast Configuration

 Description This article covers the configuration required to run the PTP TC with multicast transport environment, and Tap Aggregation DUT time sync with PTP GM. Platform Compatibility DCS-7020 DCS-7280SE/ DCS-7500E DCS-7280R/RX DCS-7500R/RX DCS-7150 DCS-7050X/XX DCS-7060X/XX Topology Diagrams     Configuration In this PTP implementation example, the NY1 will act as BC and NY4 as GM. Both are configured as PTP BC clocks but NY4 due to its lower Priority1 value will win the BCMA election and becomes the master. The NY2 and NY3 are configured as E2E TC clocks and will require PIM to forward the PTP messages generated by...
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Configure Daemon Script to Collect Data

Summary The EOS daemon command is typically used to run TerminAttr (Streaming Telemetry Agent) on Arista switches. The daemon command can also be used to create custom daemon processes to do just about anything you wish. It can be useful in troubleshooting and collecting data over a period of time. In the example below, we create a bash script that runs 4 show commands and adds a timestamp to the log and repeats the process every 5 seconds. The output of the script commands are stored in an agents file located in /var/log/agents. Create Script File From the switch, drop...
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Recovering a switch from Aboot

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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Wireshark LUA dissector for “Mirroring to GRE with Timestamping” feature

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

IGMP Host-proxy

Interfaces on the switch can be configured to serve as IGMP host proxies. An IGMP host proxy exchanges IGMP reports (joins/leaves) between networks whose connection does not support PIM along network boundaries. Let’s take the example shown below: The customer network connects to the sender network through the edge switch’s Ethernet 1 interface, which is configured as an IGMP host proxy. PIM is enabled within the publisher and customer networks but not on the connection between the networks.   When only “ip igmp host-proxy” is configured on the interface, IGMP reports will be sent for any (*,G) or (S,G) entry...
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Configuring the Campus Voice VLAN

Overview This article is intended to discuss how to configure the Voice VLAN (phone VLAN) on a 720X Arista switch. Introduction In the Campus environment, there are myriad devices which can connect wirelessly or wired. Switches need to be able to classify these devices and forward the traffic appropriately. For IP phones, this is of utmost importance as Voice traffic and Voice signaling need to be treated with priority over generic data traffic to ensure quality of service and minimum to no loss. This article focuses on how to configure the switch CLI based on different scenarios found on a...
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Troubleshooting Dequeue deletes on 7280/7500 devices

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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ZTP with Arista Switches

Overview This article is intended to discuss zero to one of ZTP. Introduction Zero Touch Provisioning(ZTP) is a feature that allows users to initially provision Arista network switches without user interaction. The switch enters ZTP mode whenever the device comes up without a start-up configuration in flash. It remains in ZTP mode until a user cancels ZTP mode, or until the switch retrieves a startup-config or a boot script. After downloading a file through ZTP, the switch reboots again, using the startup configurations from the retrieved file. To provision the switch through Zero Touch Provisioning Step 1: Mount the switch...
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Replacement of MLAG peer switch

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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Buffer tuning for output discard mitigation

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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PTP Best Master Clock Algorithm (BMCA)

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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Routing Context – Management VRF and Logs backup

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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Troubleshooting EVPN IRB with VXLAN

Overview This article provides a brief introduction to EVPN IRB with VXLAN along with basic debugging methods for the same. Introduction Ethernet VPN (EVPN) is an extension of the MP-BGP protocol introducing a new address family. EVPN is used as a control-plane for VXLAN environments to exchange information such as MAC addresses and ARP bindings along with VTEP flood list. Additionally,  IP prefixes can be exchanged in the overlay using Type-5 routes.  Platform Compatibility The below table captures the EVPN IRB support for a few Arista platforms: on the platforms listed below:   Platform Feature Support EOS Release 7050X/ 7300X/...
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Dot1q tagged LACPDU

Introduction This document provides details on how 802.1Q tagged LACP packets are handled on our Arista device. 802.1Q tagged LACP PDUs The LACP PDU frames were ingressing from other vendors into an Arista switch with an 802.1Q tag and designated as VLAN 0. 10:03:58.521076 58:ac:78:f2:8c:05 > 01:80:c2:00:00:02, ethertype 802.1Q (0x8100), length 128: vlan 0, p 0, ethertype Slow Protocols, LACPv1, length 110 10:03:59.421028 58:ac:78:f2:8c:05 > 01:80:c2:00:00:02, ethertype 802.1Q (0x8100), length 128: vlan 0, p 0, ethertype Slow Protocols, LACPv1, length 110 Natively, EOS discards tagged LACP PDUs as they are out of spec. These discards can be observed using the...
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LACP Rate Fast

Introduction The LACP rate fast feature is used to set the rate (once every second) at which the LACP control packets are sent from partner. The normal rate at which LACP packets are sent is 30 seconds. This document provides workflow of the LACP rate fast feature including the packet capture and some recommendations/concerns in MLAG setup. How it works When LACP is synchronizing between two device LACP PDUs are sent at a rate of 1 per second until both sides are synchronized. Once this is complete they are sent at a rate of 1 per 30 seconds. LACP Rate...
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Troubleshooting sFlow

Overview This document aims at providing the basic checks that can be performed for troubleshooting sFlow. Introduction Arista switches provide an sFlow agent that samples only ingress traffic from all Ethernet and port-channel interfaces. This agent combines the interface counters and flow samples into sFlow datagrams that are sent to a sFlow collector. A sFlow collector is a server that runs software which analyzes and reports network traffic. Arista switches do not include sFlow collector software. The switch sends sFlow datagrams to the collector located at an IP address specified by a global configuration command. If the collector destination is...
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Console Troubleshooting Guide

Objective The objective of this document is to outline the common issues faced while using a console cable/server to access an Arista Switch. This document lists the troubleshooting steps to isolate the issue with these connections. Introduction In order to access the device, we use either an SSH or a Console connection. Normally, the console port is used for serial access to the switch and is used in the following cases: • initial provisioning of the device manually (when the management ports are not assigned IP addresses) • the device is inaccessible remotely via SSH Please refer to the appropriate...
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