Test 2 Study Guide Flashcards
What IEEE standard added full duplex flow control?
Full duplex flow control was added as a part of IEEE 802.3X.
What is full duplex flow control?
Full duplex flow control is a reference to IEEE 802.3X, wherein a station operating in full-duplex can send a PAUSE frame to the multicast address, wherein the sender will know to delay further transmission by the amount of time specified in the frame.
What IEEE standard added the Spanning Tree Protocol?
The Spanning Tree Protocol was added in IEEE 802.1D.
What is the spanning tree protocol?
Spanning tree protocol is a network protocol that ensures the absence of any network loops within a network layout that would normally have them. It exchanges data between bridges to build a picture of what the whole network looks like.
How does the spanning tree protocol work?
The spanning tree protocol first sends out Bridge Protocol Data Units from each switch to determine the network topology. It then decides which bridge will become the “root bridge”, the bridge that will act as the controller for STP. This is by default the bridge with the lowest IP address.
The next step is to identify root ports. There will be only one root port per bridge, which is the one with the shortest path to the root bridge.
After the root ports are set, designated ports are set, as are blocked ports. A designated port is always at the other end of a root port, and on connections where there is no root port, one becomes designated (the one with the lower address), and the other becomes blocked.
What are Bridge Protocol Data Units?
Bridge protocol data units are packets that are sent out by bridges in an spanning tree protocol network periodically, that contain information about the network’s setup.
What is a root port? How is it identified?
A root port is a port that is on the shortest path back to the root bridge.
What is a root bridge? How is it identified?
A root bridge is a concept in the spanning tree protocol where the switch with the lowest MAC address becomes the “controlling” switch.
What is a designated port?
A designated port is a port in the listening state. All ports on the root bridge are designated ports. In the case where a port could be either designated or blocked, the port with the least cost will become designated; if they are tied, the one with the lowest ID will become designated.
What IEEE standard implemented Rapid STP?
IEE 802.1W implemented Rapid STP.
What is Rapid STP?
Rapid STP, or rapid spanning tree protocol, is a variant of the spanning tree protocol, but it provides a significant speed increase in recovery after a topology change.
What IEEE standard implemented link aggregation?
IEEE 802.3AD implemented link aggregation.
What is link aggregation?
Link aggregation is a method of combining multiple network connections in parallel in order to increase throughput. It was implemented in IEEE 802.3AD
In what IEEE standard implementation was Quality of Service implemented?
Quality of Service was implemented in IEEE 802.1P.
What is Quality of Service?
Quality of service is a method of determining the order by which traffic should be processed, based on its priority.
What are the three main standards of Quality of Service?
The three main standards of Quality of Service are Voice Service, Gold Service (data), and Best Effort (data). Best effort means the best effort will be given to process it, after everything else is done.
What is the operation mode of most modern Ethernet switches?
Most modern Ethernet switches operate in store-and-forward mode. This is because it allows for error checking, and with the speed of current switches, there’s no loss of service.
What are the states of STP? What happens in each?
The states of STP are:
- Listening - Will only send/receive BPDU to participate.
- Learning - Same as listening, but it will populate its MAC table to become a forwarding state later.
- Forwarding - Forwards frames and sends/receives BPDU.
- Blocking - Only receives BPDU
- Disabled - Will not send or receive BPDUs or data.
What are the states in RSTP? How are they different from STP?
The states of RSTP are:
- Discarding - No user data is sent over the port.
- Learning - Still not forwarding frames, but populates MAC table
- Forwarding - Normal operation.
What are the timers used in STP? What do they each do?
STP’s timers are:
- Aging Timer: How long a MAC address is kept in a bridge’s forwarding database after having received a packet from that address. 300s default.
- Forward Delay Timer: Time spent in Listening & Learning before entering Forwarding. 15s default.
- Hello Timer: The interval at which BPDU packets are sent out by the root & designated bridges.
- Max Age Timer: If the last received hello packet is older than this timer, a topology change has occurred.
What is the primary advantage of RSTP vs STP?
The prime advantage of RSTP is that its fail-over time is considerably shorter.
How does RSTP differ from STP in regards to BPDUs?
In RSTP, all bridges generate “Hello” BPDU packets to “keep alive” the current configuration.
How does Half Duplex Ethernet implement the flow control function?
Half duplex Ethernet implements flow control by using backpressure; that is, it sends a frame back down the line in order to cause a collision.
What is the MAC control frame defined in 802.3x?
The MAC control frame defined in 802.3x is PAUSE. The PAUSE frame is usable only in full duplex, and requests that the sender waits an amount of time specified in the frame before continuing to send.
How many VLANs can be defined by the 802.1Q standard?
The 802.1Q standard can define up to 4096 VLANs. This is because there is a 12-bit field within the tag control information for the MAC frame. 2^12 = 4096
. What is the max frame size of an 802.1Q tagged frame?
The maximum frame size of an 802.1Q tagged frame is 1522 bytes.
If the Hello Timer is 2 seconds, which is the general (e.g., non LOS) failure detection time in RSTP?
The general failure detection time in RSTP will be 6 seconds, if the Hello Timer is 2 seconds. This is because in RSTP, a failure is detected if a Hello isn’t received three times in a row. 2 x 3 = 6 seconds.
How do switches/bridges exchange control information with one another?
Switches/Bridges exchange control information through the use of Bridge Protocol Data Units, or BPDUs.
How many priority queues can be specified in an 802.1p-enabled frame?
There can be up to 8 priority queues in an 802.1p-enabled frame. This is because in an 802.1p-enabled frame, there is a three-bit field for user priority. 2^3 = 8 priority queues.
The VLAN ID is added to a 802.1Q-tagged frame by what?
The VLAN ID is added by the “ingress switch”, basically, the port that traffic passes through to join the VLAN.
How is expected throughput calculated?
Expected throughput is calculated out using the following equation:
(Frame Size - 18) / (8 + Frame Size + 12) * Bandwidth