How is the virtual MAC address derived for reth interfaces on J-Series and SRX?
A reth interface is used with JSRP clustering on J-Series and SRX. Reth interfaces use two member links of which one is active for a redundancy group at any given time. As such reth interfaces have their own virtual MAC address which differs from the physical MAC address of each member link. The virtual MAC assigned is based on cluster and interface ID.
The cluster ID can be 1-15 for all Junos OS versions up to 12.1X44. Beginning with 12.1X45-D10, the cluster ID range has been extended to 1-255.
The format for all Junos OS versions up to 12.1X44 is as follows:
| 1 | 2 | 3 | 4 | 5 | 6 |
| 00 | 10 | db | ff |C|C|C|C|R|R|V|V|I|I|I|I|I|I|I|I|
The first 4 octets are always the same (00:10:db:ff). The last 2 octets are defined as below.
CCCC – Cluster ID, based on ID assigned by the user (1-15)
RR – Reserved. (always 00 at this time).
VV – Version, 00 for the first release
IIIIIIII – Interface ID, derived from the reth index value.
The format for Junos OS 12.1X45 and later is as follows:
LLLL (4-bit) : Low Order Bits of Extended cluster id
HHHH (4-bit) : High Order Bits of Extended cluster id
IIIIIIII (8-bit) : Interface id, derived from the reth index.
Note that due to the above standard virtual MAC address convention, it is possible to have a MAC address conflict if more than one JSRP cluster exists on the same layer 2 environment. Therefore it is advised that if there is more than one J-Series or SRX JSRP cluster in your environment, then use a different cluster ID for each cluster to avoid conflicts.