Layer 2 Networking Flashcards
What is 802.1D
Common spamming tree
What are the port roles for STP (802.1D)
Disabled – Port is admin shut down.
Blocking – port is not forwarding any traffic to prevent loops it will on receive BPDU’s
Listening – port is still blocking (Can send and receive BPDUs)
Learning – The port can now modify the MAC address table. It only forwards BPDUs
Forwarding – the port can now forward all traffic and fully update MAC table.
Broken – Port detects problem and port is broke until fixed.
What are the port types for STP (802.1D)
Route Port (RP) – the route port is the port that faces or connects to the route bridge on any switch in the spanning tree topology. There should only be one per VLAN per switch.
Designated Port (DP) – A port that receives and send BPDUs to other switches. They provide connectivity to downstream switches, there should only be one per link.
Blocking Port (BP) – A port not forwarding traffic due to STP calculations.
how many types of BPDUs are there and what is their purpose?
Configuration BPDU - includes all info on the STP topology and timers.
Topology change BPDU - information relevant to recent topology changes.
What is the default system priority for STP?
32768
What is the STP ‘max age timer’ and what is the default value?
Maximum amount of time a switch will hold on to the BPDU information before assuming the root sending the BPDUs is down.
Default timer 20 seconds
What is the ‘hello timer’ and what is the default value
The time interval between BPDU packets been sent out.
default is 2 seconds.
What is the ‘forward delay’ and what is the default value
The amount of time the STP switch stays in listening & learning state.
default is 15 seconds.
What determines which switch becomes the root bridge?
The switch with the lowest root bridge priority.
How is the root port identified on a bridge, if there is a match what next?
- Interface with the lowest STP path cost to the root bridge.
- Interface with the lowest system ID.
- Interface with the lowest MAC address.
- Lowest port priority of neighbouring switch.
- Lowest port number of local switch.
The designated/blocking ports are decided on the same method as the root port.
True or False.
True.
What happens when there is a topology change? e.g. link failure.
- Link failure detected on a switch.
- hat switch sends out a configuration BPDU with the TCN flag set.
- All switches flush there MAC address tables of MACs older than 15 seconds (this is in order to maintain comms with switches still active.)
What is 802.1W
RSTP
What are the 802.1W RSTP port states
Discarding
Learning
Forwarding
What is the benefit of PVST/PVST+ over 802.1D
It allows multiple spanning tree instances on a Layer 2 topology by having one vlan per spanning tree topology.
What is Rapid PVST
It combines RSTP quick convergence with cisco’s PVST protocol to allow multiple vlan’s in the layer 2 topology.
What is the main benefit over MST over PVST
MST allows multiple vlans with the same spanning tree instance to be mapped to one Multi spanning tree instance therefore reducing CPU resources.
What is a MST region
A group of MST switches with the same configuration parameters set.
When using the STP root primary and root secondary command to set the root bridge priority, what are the values of primary and secondary?
Primary: 24576
Secondary: 28672
What is the default for STP port priority
128
What does the root guard command do?
Prevents the port from becoming a root port, this is to prevent downstream switches from becoming the root bridge.
What happens if a superior BPDU is received on a port with Root guard configured?
Port is errdisabled
What does the command STP portfast do?
This is used to increase convergence speed on network edge ports as it puts the port from blocking to forwarding immediately.
What does BPDU guard do?
If a BPDU is received on a port with the guard the port will errdisable
What does the BPDU filter command do?
Prevents BPDUs from being sent out of a port.
What is UDLD used for?
Fibre optic link monitoring to prevent L2 loops.
What are the different modes of UDLD
UDLD aggressive - if 1 frame not ack, 8 quick frames sent if not ack errdiabled.
UDLD normal - no ack
What is VTP?
Vlan trunking protocol is an old protocol used to deploy vlans to a L2 topology before APIs useful with a lot of switches.
What are the different VTP roles?
VTP server - sends out VLAN updates to all the clients.
VTP client - sets its VLANs to match the server.
VTP transparent - allows VTP comms through itself but does not partake in VTP.
VTP off - no VTP comms allowed through the device.
How many VTP advertisement types are there and what are they?
3.
VTP summary
VTP subset
VTP client request
What is the VTP summary advertisement?
Every 300 seconds or when VLAN added.
This is to compare with other switches to ensure that other switches VLAN databases are the same by comparing the revision number.
Includes:
1. VTP version
2. VTP domain
3. VTP configuration revision.
What is the VTP subset advertisement?
After any VLAN change occurs.
Includes:
ALL relevant information on the VLAN.
What is the VTP client request advertisement?
Requested by the client for more information on a specific VTP domain.
What is the warning with VTP
Check VTP configuration number before adding a switch to a VTP domain as higher number can send out VLAN updates including deleting them!
What is DTP used for
Dynamically communicate to determine whether 2 ports can from a trunk link.
How often does DTP advertise to maintain relationship?
30 seconds.
What are the different trunk modes
switchport mode trunk - static
switchport mode dynamic desirable - DTP
switchport mode auto - DTP
What does switchport nonegotiate do
prevents a static switchport from negotiating with a dynamic DTP port.
What is the purpose of Ether-channels
To aggregate multiple links between the same devices.
What are the different types of ports that can have a EtherChannel configured on them
Routed
Switchport
Trunk
What are the 3 ways to configure a etherchannel?
Static
PAgP
LACP
What are the modes for PAgP
desirable
auto
What are the modes for LACP
active
passive
