DokuWiki

• number block – family
  • 70xx fixed switching
  • 72xx deep-buffer fixed
  • 75xx modular chassis

• first letter
  • X - high-performance fixed (Trident / Tomahawk)
  • R - deep-buffer routing (Jericho)
  • S - scaled tables

• port letters (after the number)
  • Q - 40 G QSFP+
  • C - 100 G QSFP28 (or 400 G QSFP-DD when paired with D)
  • D - QSFP-DD 400 G
  • O - OSFP 400 G
  • Y - 25 G SFP28
  • T - 10GBASE-T copper

• suffixes
  • A / F - airflow (A front-to-back, F back-to-front)
  • M - large memory for huge routing tables
  • K - inline MACsec / crypto
  • R3 - third hardware generation

ARISTA
To enable scp on the management vrf:

$ sudo ip netns exec ns-management bash

All the tech support files are periodically saved in /mnt/flash/schedule/tech-support

SYSLOG MESSAGES
See this link for a complete list of syslog messages.
Terminal console: always on
Terminal monitor:

term mon
term no mon
sh terminal ! To see which terminal I am on

To change the logging level:
For the console:

IOU1(config)#logging console ?

For the terminal (tty):

IOU1(config)#logging monitor 

Logging to your terminal for debugging purposes. See this link.

CLI

bash

To see the SFP types - transceivers:

show interfaces phy detail  ! long reply
show transceiver status interface Ethernet14/1  ! specific reply
show idprom transceiver

Troubleshooting with Arista switches link

ARISTA SCRIPTING

find-the-next-free-vlan-id
introduction-to-managing-eos-devices-annex-b-eos-tips-for-power-user

This is to list the IP addresses and have them ordered (-n order numbers , -t . user dot as separator -k i i order first by the i digits)

sh ip int brie | awk '{print $2}' | sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4

ARISTA MLAG

sh mlag
sh mlag interfaces
show mlag config-sanity

• https://community.cisco.com/t5/switching/nexus-vpc-to-arista-mlag/td-p/2709929
• https://eos.arista.com/mlag-basic-configuration/
• https://eos.arista.com/forum/error-mlag-config-sanity/

FIRST BOOT

localhost login: admin # and no password
en
zerotouch disable # the device reboots

EOS UPGRADE:
Arista firmware upgrade (not Aboot boot-loader for the switch (which is really a Linux system))

scp  EOS-4.18.2F.swi admin@192.168.160.102://mnt/flash/EOS-4.18.2F.swi 
Or directly with WinSCP. Use H: as local drive
dir flash:
verify /md5 flash:EOS-4.25.5.1M.swi
conf t
boot system flash:EOS-4.25.5.1M.swi   ! no need to save after ths
reload now

ARISTA SHELL (LINUX):
https://eos.arista.com/traffic-generator-on-arista/#3_Generating_Multicast_traffic

en
bash 
sudo -i
tcpdump 
iperf..
mz..

AUTOMATION

ANSIBLE
Arista_Ansible_in_a_different_section

Features:

• Signal regeneration
• Port mirroring
• Dynamic patching/link management
• Ad-hoc tapping without rewiring
• Layer 1+ statistics on every link
• Media conversion
• Telemetry and more
• Cut-Through Switching (below expanded)

Cut-through switching allows forwarding frames as soon as the destination MAC is read (6 bytes), without waiting for the full packet. This enables extremely low-latency forwarding, ideal for HFT environments where every nanosecond counts.
Switching Modes

• Cut-through: Starts forwarding after 6 bytes (DMAC). Fastest, no CRC check.
• Fragment-free: Waits for 64 bytes to reduce early collisions. Legacy, rarely used.
• Store-and-forward: Waits for full frame and verifies CRC. Safer, slower.

Trade-offs

• No CRC/FCS verification – errors propagate to the end host.
• Risk of retransmission if frames are corrupted.
• Not always viable with VOQ & crossbar fabrics due to internal queuing or HOL blocking. Virtual Output Queuing prevents head-of-line blocking by organizing separate queues for each destination at every input port. Crossbar fabrics create a matrix architecture where multiple inputs connect simultaneously to multiple outputs. Together, they enable high-throughput, low-latency switching critical for modern data center networks.

In HFT Environments

• Critical for market data and order latency minimization.
• Typically used in clean, controlled networks with reliable links.
• Acceptable trade-off: CRC skipping vs. latency gains.

Hardware Notes

• Arista 7128X, Cisco Nexus 3500, Exablaze support true cut-through.
• Some switches offer hybrid modes or revert to store-and-forward under congestion.
• Internal architecture (e.g. VOQ + single-stage fabrics) can limit practical use.

Summary: Cut-through switching reduces latency by forwarding packets before they are fully received. It skips CRC checks but is widely used in HFT due to its performance gains in controlled, lossless environments.

TCPDUMP
External Link

Arista(config)#bash tcpdump -nevvvi any '((port 22) and (host 172.22.26.209))'

More examples here

CLOUDVISION (automation)
Streamed telemetry.

• Internally Arista is Push/Subscribe model (not polling, polling is bad!). Sysdb.
• State streaming. Events to systemd

ARISTA VRRP (ALTERNATIVE)
https://www.arista.com/en/um-eos/eos-varp aka Anycast gateway.
Same MAC in both routers. First one picking up the packet will route it anyway.

BGP COMMUNITIES

! R1
route-map COMMUNITY permit 10
set community 100:999   # erases previous comms. use 'add'
router bgp 100
network 94.70.40.0 mask 255.255.255.0 route-map COMMUNITY
neighbor 80.50.0.2 send-community    # comms. are transitive but we need this
! R2
ip community-list 10 permit 100:999    # when 'receiving' a community we need to 'define it' beforehand
route-map R1_IN permit 10
match community 10
set local-preference 150    # we can also delete parts of the comm. with set community-list <comm> delete
router bgp 200
neighbor 80.50.0.1 route-map R1_IN in
!
sh bgp neighbors 10.1.0.14 received-routes detail

ARISTA REST-API PYEAPI

• https://saidvandeklundert.net/2019-08-06-arista-eapi-using-pyeapi/
• https://pyeapi.readthedocs.io/en/latest/quickstart.html#connect-to-a-node

Using https gives SSLv3 erros with python3.10+. This is to enable higher ciphers and add the certificates: Link
The quick and dirty solution is to use port :80

! In the arista side:
management api http-commands
  protocol http
username restapi privilege 15 secret restapi
!
In the 'python' side:
  import pyeapi
import pprint
eapi_param = pyeapi.client.connect(
    transport='http',
    host='192.168.121.101',
    username='restapi',
    password='restapi',
    port=80,
)
eapi = pyeapi.client.Node(eapi_param)
version_info = eapi.run_commands(['show version',])
pprint.pprint(version_info)

External Link

scp new.cfg admin@SW1:/mnt/flash/new.cfg    ! scp the new config to the switch
! ssh to the switch
dir flash:    ! check new.cfg is there
copy running-config flash:prechange.cfg    ! make a checkpoint (golden backup of current running)
wr
reload in 10    ! failsafe
configure replace flash:new.cfg    ! do the config replace
!
! wait until 9 mins to be sure not locked out due to routing reconverging down thee line!
reload cancel    ! if all looks good, cancel the reload
! configure replace flash:prechange.cfg     !  only if you need to roll back, restore the checkpoint