A new VLAN works on one switch but not across the trunk
Hosts in VLAN 30 communicate on the same access switch. A host in VLAN 30 on the neighboring switch is unreachable. The inter-switch link is up and other VLANs cross it successfully.
Your troubleshooting taskWhich trunk evidence should you compare before adding routes or changing endpoint addresses?
Review the evidence-led approach
A reasoned approach. Verify that VLAN 30 exists where required, is allowed on both ends of the trunk, and has consistent 802.1Q and native-VLAN settings. Then confirm spanning-tree state for VLAN 30. An operational link does not prove every VLAN is carried.
Why the shortcut fails. Adding a static route cannot repair a Layer 2 VLAN that never crosses the trunk, and allowing every VLAN broadens the fault domain without explaining the mismatch.
Check your work. Record the access VLAN, trunk mode, allowed list, native VLAN and spanning-tree state on both switches, correct only the mismatch and retest from both sides.