That is the output of the MIB OID for interface index.
The interface index is not only used for ports but also for VLANs, mgmt port, virtual router,...
That is the reason it's just a number and not e.g. ge.1.1
![e21cdfde71a347b1a05bca25bbbd2802_RackMultipart20180926-55360-17zf23a-XMC_MIB_interface_index02_inline.png e21cdfde71a347b1a05bca25bbbd2802_RackMultipart20180926-55360-17zf23a-XMC_MIB_interface_index02_inline.png](/t5/image/serverpage/image-id/862i36455B5BFF6471C9/image-size/large?v=v2&px=999)
You'd use the OID ifName=1.3.6.1.2.1.31.1.1.1.1 instead which gives you the e.g. 1:1 instead.
![e21cdfde71a347b1a05bca25bbbd2802_RackMultipart20180926-42371-20i4ss-XMC_MIB_interface_index03_inline.png e21cdfde71a347b1a05bca25bbbd2802_RackMultipart20180926-42371-20i4ss-XMC_MIB_interface_index03_inline.png](/t5/image/serverpage/image-id/5795i4854DDFDDA2C76F8/image-size/large?v=v2&px=999)