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
What are the fields of the 802.1q header?
TPID (Tag Protocol identifier) and TCI (Tag Control Information)
What are the sub-fields of TCI?
PCP, DEI and VID
What is the TPID field do?
Always set to 0x8100 - this indicates dot1q tagged
What is the PCP sub field for TCI?
Priority Code Point, 3 bits, used for class of service which prioritizes traffic in congested network
What is the DEI sub field for TCI?
1 bit, used to indicates frames that can be dropped if the network is congested
What is the VID sub field for TCI?
12 bits, indicates the VLAN the frame belongs to
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VTP
Vlan Trunking Protocol
What is VTP and why is it important
It allows you to manage VLANs from a centralized switch.
What are the three modes?
Server, client and transparent
What is a VTP domain?
A VTP domain is a group of switches that share VTP information.
What is sever mode?
Allows you to add, modify, and delete VLANs. Uses the configuration revision number to compare changes, make changes. It uses the configuration revision number, and advertise it via VTP messages to other switches. Can save VLAN to NVRAM
What is client mode?
Depends on VTP server for VLAN information. It can not make any changes in VLAN information itself. Does not generate VTP messages.
What is transparent mode?
Locally significant, therefore it can add, modify, and delete VLANs. Propagates VTP messages, and saves VLANs to NVRAM.
What are the three protocols?
PAgP, LACP, Static Etherchannel
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Etherchannel - what is it
Algorithm used for load-balancing. Selection criteria based on: source mac, destination mac, source IP, destination IP, source and destination MAC/IP.
What is PAgP?
dynamically negotiates the creation/maintenance of the EtherChannel
What is LACP?
Same thing as PAgP
What is static?
Interfaces are statically configured to form an etherchannel
What are the five modes to determine which protocol is used?
On, auto, passive, active and desirable
Easy one first - on mode?
Enables etherchannel only
Active mode?
enable LACP unconditionally
Auto mode?
enable PAgP only if PAgP is detected
Desirable mode?
enables PAgP unconditionally
Passive mode?
enables LACP only is LACP device is detected
PAgP: desirable vs desirable/ auto vs auto / auto vs desirable
auto + auto = no , auto + desirable = yes, desirable + desirable = yes
LACP: active + active, active + passive, passive + passive
active + active = yes, active + passive = yes, passive + passive = no
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