Hi B,
Please refer to the Disabled port in channelized port (figure 2) for clarity about this.
https://www.juniper.net/documentation/en_US/release-independent/junos/topics/topic-map/qfx10000-line-cards.html#jd0e63
If you see the diagram, you can see that ports are numbered as (0,1) in one column, (2,3) in the second column, (4,5) the third column and so on.
Let me represent it here for you: ( underlined ports are 5th ports in each row)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Considering each row in the above representation, except for the first set which seems like 4th port is disabled ( but if you imagine the above rows as a loop, here also the fifth port is disabled if you consider 28,0,2,4 which are available, 6 becomes 5th port and in the second row similarly 7 becomes disabled 5th port while 29,1,3,5 are available)
Example: 28,0,2,4 are available and 6 is disabled --- ROW 1
29,1,3,5 are available and 7 is disabled --- ROW 2
8,10,12,14 are available and 16 is disabled ---- ROW 1
9,11,13,15 are available and 17 is disabled --- ROW 2
18,20,22,24 are available and 26 is disabled --- ROW 1
19,21,23,25 are available and 27 is disabled --- ROW 2
If you want to continue with next port, it is 28 in ROW 1 and 29 in ROW 2, applying the same fifth port disable the rule, you will get the first combination again----- 28,0,2,4 are available and 6 is disabled ( row 1) and 29,1,3,5 are available and 7 is disabled (row 2)
I hope this clarifies your doubt now.
Please mark "Accept as Solution" for this post if this helps you.
Kudos would be much appreciated too 🙂