Trunk native VLAN is VLAN 1
At a glance
Base severity
Area
Platform
Evidence level
Benchmark reference
Reads the export, not the device
ConfigProof reads a configuration export. This control is evaluated against the objects in that file, and it reports what the file says. It does not connect to the device and sees no traffic, so a finding here describes the configuration, not what the firewall is doing right now.
Why it matters
Untagged traffic on the trunk lands in VLAN 1, which also carries control protocols; double-tagging attacks can reach other VLANs through it.
How to fix it
Web interface
The steps below are written for the web interface. A finding raised on your own export carries the same steps with your object names filled in.
- Set an unused, dedicated VLAN as the native VLAN on both ends of every trunk.
Command line
Cisco IOS-XE CLI
configure terminalvlan <unused-vlan>name NATIVE-UNUSEDexitinterface <interface>switchport trunk native vlan <unused-vlan>endwrite memory
An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. Typed in configuration mode; copy running-config startup-config saves it, with no separate commit. Read every line first.
Read it back
show interfaces trunkValues to fill in2
- <unused-vlan>
- An unused VLAN reserved as the native VLAN
- <interface>
- Each affected port
Before you type it3
- Written from the Cisco IOS-XE 17 and NX-OS 9 and 10 command references and not run on a device: read each line before you paste it.
- Repeat the interface lines for every affected port, or use interface range.
- The far end has to offer the same proposal, so coordinate the change with whoever runs it.
How to confirm the fix
- show interfaces trunk shows a native VLAN other than 1.
Limits
- No limitation is recorded for this control beyond the one that applies to all of them: it reads a configuration export.
Compliance references
No benchmark recommendation is mapped to this control in this version.
More in Interfaces and Segmentation
- SW-SEC-006Edge ports without BPDU guard
- SW-SEC-007Ports negotiating trunking (DTP)
- SW-SEC-009Trunk carries every VLAN
- SW-SEC-010User ports in the default VLAN
- SW-SEC-011DHCP snooping not enabled
- SW-SEC-012Dynamic ARP inspection not enabled
- SW-SEC-016VTP in server or client mode
- SW-SEC-017vPC peer link with no separate peer keepalive
See it on your own firewall
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