Accelerated Software Upgrade (ASU)

The Accelerated Software Upgrade (ASU) process significantly decreases downtime and packet loss during a software upgrade in three ways:

  • performing time-intensive tasks (including copying the EOS image) before rebooting the control plane.
  • forwarding packets in hardware (based on the last known state) while the control-plane is offline.
  • optimizing the boot process by performing only tasks essential for software upgrade.

After the control plane has fully loaded, the data plane is restarted, causing approximately 30 seconds of downtime.

Upgrading the EOS image with Accelerated Software Upgrade

Using ASU to upgrade the active EOS image is a five-step process:

  1. Check the ASU process compatibility (Check ASU Process Compatibility)
  2. Prepare switch for upgrade (Prepare the Switch).
  3. Transfer image file to the switch (Transfer the Image File for ASU). (Not required if desired file is on the switch).
  4. Modify boot-config file to point to the desired image file (Modify boot-config).
  5. Start the ASU process (Start the ASU Process).
  6. Verify that switch is running the new image (Verify).

Check ASU Process Compatibility

The ASU process is applicable only to upgrades and only on certain systems running a compatible version of EOS. Before running the reload fast-boot command, use the following commands to check for support of the feature and to ensure that other affected features are configured appropriately.

switch#show reload fast-boot
No warnings or unsupported configuration found
Note: The checks are for conditions that are necessary but do not cover all features. The following commands check for other features that may be affected.

BGP Graceful Restart Configuration

BGP and MP-BGP must have graceful restart enabled with a restart time of at least 600 seconds a for hitless restart. Use the graceful-restart command to update the configuration as needed.

The following commands configure the BGP graceful restart time to 600 seconds.
switch(config-router-bgp)#graceful-restart restart-time 600

OSPF Graceful Restart Configuration

OSPF must have graceful restart enabled with a grace period of at least 600 seconds for a hitless restart. Use the graceful-restart command to update the configuration as needed.

The following commands configure the OSPF grace period to 600 seconds.
switch(config-router-ospf)#graceful-restart grace-period 600

Spanning-tree Configuration

Spanning-tree is not supported with ASU and should be disabled.

Prepare the Switch

Before upgrading the EOS image, ensure that backup copies of the currently running EOS version and the running-config file are available in case of corruption during the upgrade process. To copy the running-config file, use the copy running-config command. In this example, running-config is copied to a file in the flash drive on the switch.

switch#copy running-config flash:/cfg_06162014
Copy completed successfully.

Determine the size of the new EOS image. Then verify that there is enough space available on the flash drive for two copies of this image (use the dir command to check the bytes free figure).

switch#dir flash:
Directory of flash:/
-rwx   293168526      Nov 4    22:17   EOS4.11.0.swi
-rwx          36      Nov 8    10:24   boot-config
-rwx       37339      Jun 16   14:18   cfg_06162014

606638080 bytes total (602841088 bytes free)

Ensure that the switch has a management interface configured with an IP addresses and default gateway. Refer the sections, Assigning a Virtual IP Address to Access the Active Ethernet Management Port and Configuring a Default Route to the Gateway (see Assigning a Virtual IP Address to Access the Active Ethernet Management Port and Configuring a Default Route to the Gateway), and confirm that it can be reached through the network by using the show interfaces status command and pinging the default gateway.

switch#show interfaces status
Port    Name     Status     Vlan       Duplex   Speed      Type
Et3/1            notconnect   1         auto    auto     1000BASE-T

Ma1/1            connected   routed     unconf   unconf    Unknown 

PING ( 72(100) bytes of data.
80 bytes from icmp_seq=1 ttl=64 time=0.180 ms
80 bytes from icmp_seq=2 ttl=64 time=0.076 ms
80 bytes from icmp_seq=3 ttl=64 time=0.084 ms
80 bytes from icmp_seq=4 ttl=64 time=0.073 ms
80 bytes from icmp_seq=5 ttl=64 time=0.071 ms

Transfer the Image File for ASU

The target image must be copied to the file system on the switch, typically onto the flash drive. After verifying that there is space for two copies of the image, use the CLI copy command to copy the image to the flash drive, then confirm that the new image file has been correctly transferred.

These command examples transfer an image file to the flash drive from various locations.

USB Memory


copy usb1:/sourcefile flash:/destfile


Sch#copy usb1:/EOS-4.14.4.swi flash:/EOS-4.14.4.swi

FTP Server


copy ftp:/ftp-source/sourcefile flash:/destfile


sch#copy ftp:/user:password@ flash:/EOS-4.14.4.swi



copy scp://scp-source/sourcefile flash:/destfile


sch#copy scp://user@ flash:/EOS-4.13.2.swi



copy http://http-source/sourcefile flash:/destfile


sch#copy flash:/EOS-4.14.4.swi

Once the file has been transferred, verify that it is present in the directory, then confirm the MD5 checksum using the verify command. The MD5 checksum is available from the EOS download page of the Arista website.

switch#dir flash:
Directory of flash:/
-rwx     293168526   Nov 4     22:17     EOS4.14.2.swi
-rwx            36   Nov 8     10:24     boot-config
-rwx         37339   Jun 16    14:18     cfg_06162014
-rwx     394559902   May 30    02:57     EOS4.13.1.swi

606638080 bytes total (208281186 bytes free)
switch#53#verify /md5 flash:EOS-4.14.4.swi 
verify /md5 (flash:EOS-4.14.4.swi) =c277a965d0ed48534de6647b12a86991

Modify boot-config

After transferring and confirming the desired image file, use the boot system command to update the boot-config file to point to the new EOS image.

This command changes the boot-config file to point to the image file located in flash memory at EOS-4.14.4.swi.

switch#configure terminal
switch(config)#boot system flash:/EOS-4.14.4.swi

Use the show boot-config command to verify that the boot-config file is correct:

switch(config)#show boot-config
Software image: flash:/EOS-4.14.4.swi
Console speed: (not set)
Aboot password (encrypted): $1$ap1QMbmz$DTqsFYeauuMSa7/Qxbi2l1

Save the configuration to the startup-config file with the write command.


Start the ASU Process

After updating the boot-config file, start the ASU process using the reload fast-boot command to reload the switch and activate the new image. If running-config has not been saved, the CLI will prompt to save any modifications to the system configuration; failure to save modifications will abort the reload.

Note: Once the system configuration is saved, there is a significant delay before the user is prompted to confirm the reload.
switch#reload fast-boot
System configuration has been modified. Save? [yes/no/cancel/diff]:y
Proceed with reload? [confirm]y
Proceeding with reload


After the switch finishes reloading, log into the switch and use the show version command to confirm the correct image is loaded. The Software image version line displays the version of the active image file.

switch#show version
Arista DCS-7150S-64-CL-F
Hardware version:    01.01
Serial number:       JPE13120819
System MAC address:  001c.7326.fd0c

Software image version: 4.14.4F
Architecture:           i386
Internal build version: 4.14.4F-1649184.4144F.2
Internal build ID:      eeb3c212-b4bd-4c19-ba34-1b0aa36e43f1

Uptime:                 14 hours and 48 minutes
Total memory:           4017088 kB
Free memory:            1569760 kB