Vol 1 Part 3: Implementing Ethernet LANs Flashcards
How do you changes the bridge ID manually for an interface?
By using the priority command
How does a switch determine which port will be the root port?
All of the links from that port to the root bridge are added together. The lowest value wins, and that port is now the root port.
What is the vendor neutral EtherChannel version known as?
Link Aggregation Control Protocol (LACP)
In Rapid STP, what state replaced the disabled, blocking, and listening states?
Discarding state
What protocol governs trunking ports?
802.1Q
What command do we use when we want to see all the the VLANs in the VLAN database and which port they are assigned to?
Show vlan brief
The priority multiple is in multiples of what number?
4096
What are the two types of STP?
802.1d and 802.1w (aka the newer and faster protocol. Also known as rapid STP).
The non-root switches require to have what between itself and the root switch?
Administrative distance
RSTP has 5 roles and 3 states. What are they?
Roles: Root, alternate, designated, backup, disabled
States: discarding, learning, forwarding
Who owns the VLAN Trunking Protocol (VTP)?
Cisco
What are the different cost values with STP?
1, 2, 19, 100
STP uses roles and states. What are the 3 roles and what are the 5 states?
Roles: root, designated, blocking
States: listening (blocks and does not forward), learning (blocks and does not forward, but learns the MAC addresses of frames received), blocking, forwarding, disabled.
What is required when connecting multiple switches that will pass multiple VLANs?
Trunking
A tag contains what with respect to the VLAN?
The VLAN ID, also known as the VLAN number
What is BPDU guard and why do we use it?
Disables a port if any BPDUs are received. This is good for ports that are supposed to be access ports and helps prevent attacks and people dropping in on a switch to take over the network.
What is the max age for hellos in STP and RSTP?
STP: 10 times the hello timer (20 seconds by default)
RSTP: 3 times the hello timer (6 seconds by default)
How are VLANs identified on the trunk link?
A tag
What command do you use to enable EtherChannel?
channel-group “number” mode on
Remember to use the same number for all commands on the same switch you are configuring EtherChannel on. The channel-group number need not be the same from switch to switch however.
What does PortFast do?
It puts a switchport into forwarding mode immediately
What is load distribution/balancing with respects to EtherChannel?
Balance traffic across active links to prevent hardware from being overwhelmed and slowing down. This creates a faster and more efficient network.
What is Dynamic Trunking Protocol (DTP)?
Determines if the port should be trunking or not by sending DTP messages
What does a designated port do?
It is a port that can be utilized to communicate between switches.
Two VLANs exiting on a single switch indicates what with respect to broadcast domains?
We have two broadcast domains. In a sense, we have two switches on one switch.
What items must be the same for interfaces to participate in port-channel (EtherChannel)?
Speed, Duplex, Operational State (access or trunk), access port and access VLAN, trunk port and allowed VLANs, trunk port native VLAN, STP interface settings
What is the default mode for load balancing known as?
src-mac
ex. port-channel load-balance src-mac
After a root bridge is elected, what will STP do with all of the interfaces on the switch?
The interfaces are all put in a forwarding state
What does the switchport access command do?
It assigns which specific VLAN we are referencing with regards to the mode we are giving it
What does the switchport access mode command do?
It grants access mode to the VLAN we referenced with the switchport access command
What error message do you get if your interface settings are not the same between two switches attempting to conduct EtherChannel?
error-disabled. Once you fix the issue, you must bounce the port to bring the interface back up.
What is EtherChannel and why do we use it with respect to STP?
Combining several parallel segments of equal speed (up to 8) between the same pair of switches. STP treats EtherChannel as a single port. This creates redundancy, as you have up to 7 ports that can go down, but STP treats that EtherChannel as a single port.
What protocol is used between two switches in order to trunk?
DTP
When trunking a port, what is inserted into the frames header by the 802.1Q protocol?
A 4 byte header containing the 12 bit VLAN ID.
What command allows you to permanently store a priority value on a switch?
spanning-tree vlan “X” priority “X”
What is a bridge protocol data unit (BPDU)?
A message that a switch sends from one switch to another switch in order to detect loops. They are used to create the spanning tree.
Originally, the STP/RSTP bridge ID Header (BID) consists of what?
A 2 byte priority field and a 6 byte System-ID field based on the MAC address.
What is the most common way to configure STP?
Rapid Per-VLAN Spanning Tree (Rapid PVST+)
What is the port on the switch referred to as if the switch has administrative distance between itself and the root switch?
root port
What does a root port do?
It is the port used on a switch to communicate with the root switch. If this port is not working, the switch will try to use a designated port.
Regular switch to switch connections when trunking normally done in what mode?
Access mode
How many root ports can a switch have?
1
What is the first thing STP will do when creating the layer 2 map?
Elect a root bridge/switch (bridge is just an older term for a switch)
What command is used for EtherChannel Load Distribution/Load Balancing?
port-channel load-balance method
How do you configure a VLAN?
- Conf t
- VLAN number name name of VLAN (vlan 10 name admin)
- interface type number (interface FastEthernet0/1)
- switchport access vlan number
- switchport access mode
If two switches must pass more than one VLAN, what must we ensure that at least one side is configured to do?
trunk
Ports connected to a hub are known as?
A shared port
What is InterSwitch Link (ISL)?
A cisco proprietary way to trunk switches. It is older than 802.1Q. REMEMBER! Switches in auto mode will default to ISL, and you cannot use ISL on one side and 802.1Q on the other.
How many root ports can the root bridge have?
0! All of its ports are designated ports so it can reach out and communicate with other switches.
What administrative mode are switchports in by default with respect to trunking?
Dynamic auto
What command tells the switch to set its priority low enough to become root?
spanning-tree vlan “X” root primary
How does a switch determine which port will be the designated port?
Similar to the root port, but it’s the port that has the lowest cost to the root on the LAN segment (From one switch to another).
When STP has finished calculating layer 2 network paths and all ports are forwarding or blocking, STP is said to be what?
converged
What command can we use when we want to see VLAN IDs, but the show interfaces trunk command wont suffice?
show interfaces interface number switchport
What does VTP do?
VTP propogates VLAN information across multiple switches via trunking. The switch acts as a server and uses a database as to what the other switches should have. VTP updates are used to determine which VLANs to add, remove, or change.
What will the interfaces on the switch do if it already has a root port and a designated port?
The switch will set all of the interfaces on the switch to blocking.
What is the default priority value assigned to each switch?
32,768
What is another name for a LAN?
Broadcast Domain
How often are BPDUs sent in regular STP?
Every 2 seconds. These Hellos are forwarded by every non-root switch on all designated ports.
What changed with respect to the bridge ID between the old version of STP and current versions?
The priority header is still 2 bytes, but it is divided into a 4 bit priority multiple and a 12 bit system ID extension which typically holds the VLAN ID. The System ID portion remains the same at 6 bytes.
What is the cost referred to as between the a switch and a root switch if it has administrative distance?
root cost
What does a blocked port do?
You can receive, but not send out. If prevents traffic from being sent to
What command enables your switch to become the root should the root bridge fail?
spanning-tree vlan “X” root secondary
Explain dynamic desirable vs dynamic auto?
Dynamic desirable initiates negotiation messages and responds to negotiation messages to dynamically choose whether to start using trunking. Dynamic auto passively waits to receive trunk negotiation messages as opposed to initiating them.
What is the purpose of the Spanning Tree Protocol?
To create a loop free environment on a switch. This includes broadcast storms (repeatedly sending a frame on the same link), MAC table instability (continuous updates of MAC Addresses), and multiple frame retransmission (multiple copies of the same frame are delivered to the intended host)
When using a Cisco phone, what vlan is used for switchport access mode and what vlan is used for switchport voice mode?
Access is on vlan 59, voice is on vlan 58
Cisco has a proprietary version of EtherChannel known as what?
Port Aggregation Control Protocol (PAgP)
What is the difference between RSTP and RPVST+ with regards to VLANs and BPDUs?
RSTP uses the native VLAN with one single spanning tree and no header/tag while RPVST+ sends the BPDUs in that VLAN with tagging (802.1Q) utilizing a separate spanning tree for each VLAN.
How do BPDUs work with respect to changing the Spanning Tree?
The root sends out a Hello BPDU with a root cose of 0 out on all working interfaces. Non-root switches receive the hello on their root ports. Afterwards, they change the BPDU with their BID as the sender, but keeps the root BID the same and sends it out on all designated ports. This continues on until something changes.
The lowest numeric value of the bridge ID is what?
The root switch
How are tiebreakers determined for designated ports?
- Lower BID wins
2. Lowest port number wins
When trying to compare values in the bridge ID, what portion of the bridge ID is examined first?
Priority is first, system-ID is second
How do we turn off DTO?
switchport mode access
switchport nonegotiate
