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