This article provides information on how to identify interface designation on Modular Interface Cards (MICs) on an MX 5/10/40/80 Series router.
How to avoid numbering conflicts on MX Series 5/10/40/80 routers.
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There are two Flexible PIC Concentrators (FPCs) on the router:
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There are four possible Modular Interface Cards (MICs) on the router:
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MIC 0/0 is built-in (FPC 0) with 4 x 10GE(LAN) XFP (10 Gigabit Small Form Factor Pluggable) ports.
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MIC 1/0 and MIC 1/1(FPC 1) can be a combination of MIC 3D 20x1GE(LAN) SFP; MIC 3D 2x10GE(LAN) XFP; or any other supported MIC (such as MIC-3D-4OC3OC12-1OC48).
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There is a fourth slot on the back of the router for multi-services MICs only. (MS-MIC-16G and appears under FPC 0 PIC 2 in show chassis hardware
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There is a potential for numbering conflicts. For example, MIC 1/0 could have the ge-1/1/0 interface and MIC 1/1 could have the xe-1/1/0 interface. This could cause a conflict.
Note: A particular MIC slot is activated depending upon which MX license is installed on the router. Here are the MICs and ports activated by license type:
The second numbers on the interfaces on the MICs that are inserted into FPC 1 are determined by the MIC slot they are inserted into.
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The first number on the interfaces on MIC 1/0 and MIC 1/1 is always 1. This represents the FPC number; for example, ge-1/x/x and xe-1/x/x.
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The last number on each row of ports on the MIC 1/0 is numbered from 0 to 9; for example, ge-1/x/0, ge-1/x/1,...ge-1/x/9.
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The second number on the interfaces on the MICs can be 1, 3, 0 or 2, depending on which MIC slot they are inserted into.
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If a MIC is inserted in MIC slot 0 on FPC 1, the second number in the interface numbering is 1 or 0. It will be 0 for the ports on the bottom and 1 for the ports of the top row on the MIC.
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If a MIC is inserted in MIC slot 1 on FPC 1, the second number in the interface numbering is 2 or 3. It will be 2 for the ports on the bottom and 3 for the ports of the top row on the MIC.
Refer to the following image:

2020-04-13: Article checked for accuracy and found to be valid and accurate; no changes made