A native VLAN mismatch on the trunk
Two switches share an 802.1Q trunk, but the two ends disagree on the native VLAN. Untagged frames land in the wrong VLAN. Align the native VLAN on both ends.
Scenario
sw1 and sw2 are joined by an 802.1Q trunk on Ethernet3. The design uses a dedicated, unused
native VLAN 99 so no data VLAN rides untagged. sw1 is set up correctly, but sw2's trunk
still uses the default native VLAN 1, a mismatch. Untagged frames on the link land in different
VLANs on each side (and switches will log the inconsistency).
Your job
In sw2/sw2.conf, set the trunk's native VLAN to 99 to match sw1, keeping VLANs 10 and 20
carried on the trunk.
What "done" looks like
Both trunk ends use native VLAN 99, and the trunk still allows VLANs 10 and 20.
Teaches: the 802.1Q native VLAN must match on both ends of a trunk: a mismatch silently bridges VLANs for untagged traffic, a connectivity and security problem. Using a dedicated unused native VLAN avoids riding a data VLAN untagged.
What gets checked
Your solution is verified against each of these:
- Both ends of the trunk use the same native VLAN
- The native VLAN is the dedicated VLAN 99, not a data VLAN
- The trunk still carries the data VLANs (10 and 20)
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