SRX

How does vSRX derive chassis base mac from Juniper-reserved MAC range at boot?

Dear all,

on en Eve-NG installation with vSRX we recognized that the vSRX gets a new random chassis base mac (show chassis mac) with every reboot.
Note: you can specify a fix MAC address for the first eth interface of vSRX, but this does not affect the random chassis base mac after each reboot.

Does anyone knows how to force the vSRX to use permanently the same chassis base mac?

It is quite annoying for vSRX WAN Assurance in MIST that the chassis base mac address is used to identify the vSRX and it changes during every boot.

I could not found any documentation about how the vSRX derives its base mac at startup nor if there are ways to make the chassis base mac permanent over reboots.

The only things found in documentation are:

On vSRX there is no physical EEPROM, so Junos allocates a virtual chassis base from a Juniper-reserved MAC range at boot and uses that as the chassis MAC base you see in this command (from which various internal/management MACs are derived).

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Perhaps more the solution is about redundancy.  If you realize an engineering station uses ospf, and that ospf probably helps us get to the problem with redundancy, you will also have to deal with topology change. That and other concepts are our challenges. So maybe that's why the randomized mac. It has to do with bridge. Independent bridge topology changes would be my explanation.

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Adrian Aguinaga
B.S.C.M. I.T.T. Tech
(Construction Management)
A.A.S. I.T.T. Tech
(Drafting & Design)
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Original Message:
Sent: 01-09-2026 02:31
From: s.funk
Subject: How does vSRX (on Eve-NG) derive chassis base mac from Juniper-reserved MAC range at boot?

How does vSRX derive chassis base mac from Juniper-reserved MAC range at boot?

Dear all,

on en Eve-NG installation with vSRX we recognized that the vSRX gets a new random chassis base mac (show chassis mac) with every reboot.
Note: you can specify a fix MAC address for the first eth interface of vSRX, but this does not affect the random chassis base mac after each reboot.

Does anyone knows how to force the vSRX to use permanently the same chassis base mac?

It is quite annoying for vSRX WAN Assurance in MIST that the chassis base mac address is used to identify the vSRX and it changes during every boot.

I could not found any documentation about how the vSRX derives its base mac at startup nor if there are ways to make the chassis base mac permanent over reboots.

The only things found in documentation are:

On vSRX there is no physical EEPROM, so Junos allocates a virtual chassis base from a Juniper-reserved MAC range at boot and uses that as the chassis MAC base you see in this command (from which various internal/management MACs are derived).

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