VTP/DTP/Etherchannel/Trunk services Flashcards
What is DTP
**Manages trunk connections. Dynamic Trunking Protocol - negotiates interfaces as trunk or access port. Link-Layer protocol. Negotiates trunking on a link between two-VLAN aware switches. Dynamically forms trunk links.
What are the four/five modes of DTP
Nonegotiate, Auto, On, Trunk, Desirable, Off
What is a Trunk link?
Carries traffic from multiple VLANs, forwards frames.
Tagged and untagged
Remember, an access interface does not understand tagged traffic. Trunk interfaces do, however.
How does DTP work?
Based on the remote port, it automatically updates the configuration of the local trunk port. It uses DTP messages to identify the remote port.
On or Trunk mode
it always assumes the remote port is a trunk port. This is bad, because if it is an access port, traffic will be dropped.
Desirable
It starts the local port in access mode. It generates DTP messages and sends them to the remote port. If it receives DTP messages (reply) back, it assumes the remote port is a trunk port and changes the local port to trunk status.
Auto
Starts local port in access mode and passively listens for DTP messages from the remote site. If it receives DTP messages from the remote port, it assumes it is a trunk port and changes its own local port to trunk.
Noneogtiate
Does not generate and send DTP messages.
Next, trunks and VLANs
What are the two types of VLAN connections?
Access and Trunk connections
How many VLANs exist?
0-4095, but 1-4094…
Tagged and untagged
Trunks tag frames, with the exception of the native VLAN
What is a trunk link?
Carries traffic from multiple VLANs. It transports the traffic with VLAN information.
What is an access link?
Carries the traffic of only one VLAN. Transports traffic with no VLAN information.
Tidbits of info on Access links
Removes all VLAN information from frames before forwarding them…unlike trunk frames. By default, all switchports are access ports.
What are the two trunking protocols
ISL and 802.1q
What are the fields of the ethernet header?
Preamble-SFD-Destination MAC - Source MAC - {dot1q}Type/length