Juniper Networks M5 - Manual (Page 196)

RJ-21 Cable Pinouts for Fast Ethernet 12-Port PIC
Table 25: RJ-21 Pin Assignments
Ethernet Port Numbers RJ-21 Pin Assignment
TX - TX + RX - RX +
0 2 27 1 26
1 4 29 3 28
2 6 31 5 30
3 8 33 7 32
4 10 35 9 34
5 12 37 11 36
6 14 39 13 38
7 16 41 15 40
8 18 43 17 42
9 20 45 19 44
10 22 47 21 46
11 24 49 23 48
176 M5 and M10 Internet Routers Hardware Guide