A network administrator is diagnosing several switching, trunking, and physical layer issues across access and core switches in an enterprise environment. Match each switch console symptom or log output on the left with its corresponding underlying root cause on the right.
- Console log: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on interface GigabitEthernet0/1 (1), with Switch-B GigabitEthernet0/1 (99).Mismatched untagged 802.1Q native VLAN numbers configured on opposing ends of the trunk link.
- Inter-VLAN traffic for VLAN 20 fails across a trunk link, while trunk status shows operational and configuration displays 'switchport trunk allowed vlan 10,30,40'.Omission of the target VLAN ID from the interface allowed VLAN list on the trunk configuration.
- Interface FastEthernet0/12 reports high counts of late collisions and FCS errors after connecting a server with a manually forced 100 Mbps Full-Duplex network adapter.Duplex mismatch caused by IEEE 802.3 auto-negotiation falling back to Half-Duplex on the switch port.
- An unconfigured switch connected to the network unexpectedly becomes the STP Root Bridge for VLAN 1 without any explicit priority modification.Default STP priority tie () resolved in favor of the new switch due to its lower MAC address.
Cevap
1. CDP Native VLAN mismatch log matches mismatched untagged 802.1Q native VLAN numbers on opposing ends of the trunk.
2. VLAN 20 traffic failure with allowed list '10,30,40' matches omission of the target VLAN ID from the allowed list.
3. Late collisions with forced full-duplex server match duplex mismatch caused by auto-negotiation falling back to half-duplex.
4. Unconfigured switch becoming STP root bridge matches default STP priority tie () resolved by lower MAC address.
2. VLAN 20 traffic failure with allowed list '10,30,40' matches omission of the target VLAN ID from the allowed list.
3. Late collisions with forced full-duplex server match duplex mismatch caused by auto-negotiation falling back to half-duplex.
4. Unconfigured switch becoming STP root bridge matches default STP priority tie () resolved by lower MAC address.
Each switch symptom directly corresponds to a distinct Layer 2 operational failure mode: CDP log warnings indicate mismatched untagged native VLAN IDs on 802.1Q trunks; missing VLAN IDs in the allowed trunk string cause explicit frame dropping for that VLAN; forced full-duplex on a connected device breaks auto-negotiation, defaulting the switch port to half-duplex and producing late collisions; and unconfigured switches claiming root bridge status stem from default STP priority ties resolved by MAC address comparisons.
Adım Adım Çözüm
Anahtar Kavram
Diagnosing VLAN tagging, trunking allowed lists, Ethernet duplex auto-negotiation, and STP root election behaviors from switch symptoms.