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[vMX] IRB interfaces in two different routers have same MAC address

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Article ID: KB36402 KB Last Updated: 31 Dec 2020Version: 1.0
Summary:

The IRB interfaces in two different vMX have the same MAC addresses. 

Cause:

The IRB interfaces MAC address is allocated from chassis MAC address pool for private address. The command below shows the output from two vMX deployed on VMWare ESXi

​root@vMX2> show chassis mac-addresses                   
MAC address information:
  Public base address      2c:6b:f5:3c:15:00
  Public count             1984
  Private base address     2c:6b:f5:3c:1c:c0
  Private count            64

root@vMX2> show interfaces irb   
Physical interface: irb, Enabled, Physical link is Up
  Interface index: 132, SNMP ifIndex: 512
  Type: Ethernet, Link-level type: Ethernet, MTU: 1518
  Device flags   : Present Running
  Interface flags: SNMP-Traps
  Link type      : Full-Duplex
  Current address: 2c:6b:f5:3c:1c:f0, Hardware address: 2c:6b:f5:3c:1c:f0
  Last flapped   : Never
    Input packets : 0
    Output packets: 0

root@vMX1> show chassis mac-addresses 
MAC address information:
  Public base address      2c:6b:f5:3c:15:00
  Public count             1984
  Private base address     2c:6b:f5:3c:1c:c0
  Private count            64

root@vMX1> show interfaces irb 
Physical interface: irb, Enabled, Physical link is Up
  Interface index: 132, SNMP ifIndex: 512
  Type: Ethernet, Link-level type: Ethernet, MTU: 1518
  Device flags   : Present Running
  Interface flags: SNMP-Traps
  Link type      : Full-Duplex
  Current address: 2c:6b:f5:3c:1c:f0, Hardware address: 2c:6b:f5:3c:1c:f0
  Last flapped   : Never
    Input packets : 0
    Output packets: 0
Solution:

This is expected behavior. The MAC address for the IRB can be changed manually using the command below:

set interfaces irb unit <unit-number> mac <mac-address>

Note the physical MAC address of the IRB interface is still the same. The logical sub-interfaces MAC address are changed to user-defined values. This is true for IPv4. The behavior of manual MAC-address change for family inet6 is detailed in KB28918 - [MX] MAC address on IRB interfaces
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