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Zorluk: ZorInterswitch Connectivity and Trunking (802.1Q)

A network administrator connects two Cisco Catalyst switches via their GigabitEthernet0/1 interfaces. Switch-A is configured with `switchport mode dynamic desirable`, while Switch-B remains in its default `dynamic auto` mode. What is the correct chronological sequence of operational events during Dynamic Trunking Protocol (DTP) negotiation to establish an IEEE 802.1Q trunk link?

  1. 1Switch-A generates and transmits a DTP frame on GigabitEthernet0/1 actively requesting to form a trunk link.
  2. 2Switch-B receives the DTP frame on its `dynamic auto` interface and parses the incoming negotiation parameters.
  3. 3Switch-B transmits a DTP acknowledgment frame confirming agreement to establish a trunk link.
  4. 4Both switches compare supported trunking encapsulation types and agree upon IEEE 802.1Q operation.
  5. 5Both switch interfaces transition their operational mode from access to trunk and begin forwarding multi-VLAN traffic.

Cevap

The correct sequence is: Switch-A transmits a DTP frame requesting a trunk, Switch-B receives and parses the DTP frame, Switch-B transmits a DTP acknowledgment frame, both switches agree upon IEEE 802.1Q encapsulation, and finally both switch interfaces transition to the operational trunk state.
The correct order follows the DTP state machine negotiation flow. A port in `dynamic desirable` mode actively sends DTP request frames to its link partner. The neighboring port in `dynamic auto` mode receives and processes this request, responding with a DTP acknowledgment frame to consent to trunking. Following parameter exchange, both switches negotiate the trunk encapsulation (IEEE 802.1Q) and finally transition both interface operational states to trunking.

Adım Adım Çözüm

1
Identify the initiating interface state and behavior
Switch-A (`dynamic desirable`) actively sends DTP negotiation frames to initiate trunking.
Interfaces in `dynamic desirable` mode actively attempt to convert the link to a trunk.
2
Determine the receiving interface processing
Switch-B (`dynamic auto`) receives the request and evaluates parameters.
Interfaces in `dynamic auto` mode do not initiate DTP requests but respond to incoming requests.
3
Trace the protocol response and handshake
Switch-B sends a DTP response agreeing to form a trunk link.
A `dynamic auto` port agrees to become a trunk when requested by a `dynamic desirable` port.
4
Resolve encapsulation negotiation
Both switches negotiate and agree on 802.1Q encapsulation.
Trunking encapsulation must be determined prior to bringing up the operational trunking state.
5
Confirm operational state transition
Both ports transition to operational trunking mode.
Once negotiation handshakes and parameters match, the link operational mode becomes trunk.

Anahtar Kavram

Dynamic Trunking Protocol (DTP) negotiation flow between dynamic desirable and dynamic auto interface modes in IEEE 802.1Q trunking.
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