Network Analysis: Read a VLAN ID from Captured Link Output

Analysis room: you read captured link output from another host and record one VLAN's ID. You don't create or configure a VLAN here.

Why: this lab box's kernel has no 802.1Q VLAN driver, built in or loadable, so no VLAN interface can exist on it, and running ip -d link here won't show one. Instead you analyse the kernel's view of VLANs captured on a host that has them.

That host's trunk was carved into several named VLAN sub-interfaces, and one of them is misbehaving. The output of ip -d link show for all of them is saved at /root/net/vlan-links.txt, and `/root/net/task.txt` names the sub-interface you're investigating. The capture and the target are generated per session, so your answer differs from anyone else's.

Find that sub-interface's block and record its 802.1Q VLAN id. The names don't encode the id, and each block also shows an ifindex, an MTU and queue counts — only the number after id on the vlan protocol 802.1Q line is the VLAN.

Write just the number to /root/answers/vlan_id.txt.