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[EX] Explanation of MAC address assignments in a Virtual Chassis



Article ID: KB32567 KB Last Updated: 01 Apr 2021Version: 2.0

This article explains the assignments of MAC addresses for Layer 2 Access/Trunk interfaces, Layer 3 interfaces and aggregated interfaces in a Virtual Chassis environment.



EX4200 virtual-chassis-----------EX4200 virtual-chassis


EX4200-VC (two members) / Junos OS 12.3R3 and 12.3 R6

MAC address of chassis:

root@switch> show chassis mac-addresses
 FPC 0   MAC address information:
      Public base address     2c:6b:f5:8b:23:00
      Public count            64
 FPC 1   MAC address information:
      Public base address     5c:5e:ab:65:2d:00
      Public count            128


FPC0 is the Primary Routing Engine

root@switch> show virtual-chassis
Virtual Chassis ID: de1c.1739.2d0f
Virtual Chassis Mode: Enabled
Member ID  Status   Serial No             Model    Mstr prio     Role     Mixed Mode    ID  Neighbor List Interface
0 (FPC 0)        Prsnt    BN0210182298 ex4200-24p       128      Master*      N                     1        vcp-1
1 (FPC 1)        Prsnt    BQ0211102296 ex4200-48p       128      Backup       N                     0        vcp-1
Member ID for next new member: 2 (FPC 2)

Four RVIs configured on the switch:

root@switch> show vlans brief
Name        Tag       Primary Address          Port Active/Total
V10           10                         0/9
V20           20                         0/9
V30           30                         0/9
default       1                          0/7

MAC address of RVIs are constant for all RVIs. The calculation of the RVI MAC address is Base MAC address of Primary Routing Engine + 1:

  VLAN              MAC address           Type         Age Interfaces
  default         2c:6b:f5:8b:23:01      Static         - Router
  V10             2c:6b:f5:8b:23:01      Static         - Router
  V20             2c:6b:f5:8b:23:01      Static         - Router
  V30             2c:6b:f5:8b:23:01      Static         - Router

Six access ports (3 on each member), e.g., ge-0/0/0, ge-1/0/0, ge-0/0/1, ge-1/0/1, ge-0/0/2 and ge-1/0/2, and mapped VLANs with their respective interfaces:

ge-0/0/0   Current address: 2c:6b:f5:8b:23:03, Hardware address: 2c:6b:f5:8b:23:03       Vlan 10
ge-1/0/0   Current address: 5c:5e:ab:65:2d:03, Hardware address: 5c:5e:ab:65:2d:03       Vlan 10
ge-0/0/1   Current address: 2c:6b:f5:8b:23:04, Hardware address: 2c:6b:f5:8b:23:04       Vlan 20
ge-1/0/1   Current address: 5c:5e:ab:65:2d:04, Hardware address: 5c:5e:ab:65:2d:04       Vlan 20
ge-0/0/2   Current address: 2c:6b:f5:8b:23:05, Hardware address: 2c:6b:f5:8b:23:05       Vlan 30
ge-1/0/2   Current address: 5c:5e:ab:65:2d:05, Hardware address: 5c:5e:ab:65:2d:05       Vlan 30

Layer 2 interfaces and their MAC address assignment is on the basis of the local chassis MAC address.

Their current and hardware address is same for that particular interface.
Two trunk interfaces are configured, which was mapped for all VLANs, e.g. ge-0/0/3, ge-0/0/4, ge-1/0/3 and ge-1/0/4.

ge-0/0/3   Current address: 2c:6b:f5:8b:23:06,  Hardware address: 2c:6b:f5:8b:23:06   Trunk
ge-1/0/3   Current address: 5c:5e:ab:65:2d:06,  Hardware address: 5c:5e:ab:65:2d:06   Trunk
ge-0/0/4   Current address: 2c:6b:f5:8b:23:07,  Hardware address: 2c:6b:f5:8b:23:07   Trunk
ge-1/0/4   Current address: 5c:5e:ab:65:2d:07,  Hardware address: 5c:5e:ab:65:2d:07   Trunk

The MAC address of trunk interfaces is derived from local chassis MAC address.

Their current and hardware address is same for that particular interface.
IP addresses are configured on six physical interfaces:

ge-0/0/5   Current address: 2c:6b:f5:8b:23:08, Hardware address: 2c:6b:f5:8b:23:08    IP:   >>>>>>> Same current address
ge-1/0/5   Current address: 2c:6b:f5:8b:23:08, Hardware address: 5c:5e:ab:65:2d:08    IP:    >>>>>>> Same current address
ge-0/0/6   Current address: 2c:6b:f5:8b:23:09, Hardware address: 2c:6b:f5:8b:23:09    IP:
ge-1/0/6   Current address: 2c:6b:f5:8b:23:09, Hardware address: 5c:5e:ab:65:2d:09    IP:
ge-0/0/7   Current address: 2c:6b:f5:8b:23:0a, Hardware address: 2c:6b:f5:8b:23:0a    IP:
ge-1/0/7   Current address: 2c:6b:f5:8b:23:0a, Hardware address: 5c:5e:ab:65:2d:0a    IP:

The current MAC address of the L3 physical interface is derived from the Primary Routing Engine.

The hardware address is the local port address of the switch on the Virtual Chassis. On the Virtual Chassis, two L3 physical interfaces have the same MAC address, for example: ge-0/0/6 has the same current MAC address as ge-1/0/6.
Two aggregated interfaces are configured (2 physical interfaces in 1 bundle):

AE0   ge-0/0/10    Current address: 2c:6b:f5:8b:23:03, Hardware address: 2c:6b:f5:8b:23:03    Trunk port
AE0   ge-1/0/10    Current address: 2c:6b:f5:8b:23:03, Hardware address: 5c:5e:ab:65:2d:0d    Trunk Port
AE1   ge-0/0/11    Current address: 2c:6b:f5:8b:23:04, Hardware address: 2c:6b:f5:8b:23:04    Trunk Port
AE1   ge-1/0/11    Current address: 2c:6b:f5:8b:23:04, Hardware address: 5c:5e:ab:65:2d:0e    Trunk Port

The aggregated interfaces have the MAC address from the Primary Routing Engine, and the hardware MAC address is a child interface MAC address. If you configure an aggregated interface as a L3, it has the same behavior as above.

Modification History:
2021-03-25: Updated the article terminology to align with Juniper's Inclusion & Diversity initiatives.
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