Hi Elton,
fab interfaces are not regular interfaces, which are used for passing traffic.
Theya re specuial interfaces used by cluster for communicating RTO's or Real Time Objects between nodes , basically session syncing information.
RTO's yes are not considered as traffic perse.
There are a set of such interfaces in SRX/Junos that need not be added to any zones,a nd hence part of default zone that can carry out normal functionality.
Interfaces with such excemptiona re viz. fab0,fab1,fxp0,fxp1,em0,em1 etc.
Theya re not regular interfaces and are special interfaces meant for spefic roles.
I hope this explains. Your question.
Rgeards,
c_r
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