Cisco 2 Chapter 1

64 bytes

How big is the collision window?

After receiving the entire frame on the ingress port, as shown in the figure, the switch compares the frame-check-sequence (FCS) value in the last field of the datagram against its own FCS calculations. The FCS is an error checking process that helps to ensure that the frame is free of physical and data-link errors. If the frame is error-free, the switch forwards the frame. Otherwise the frame is dropped

How does a switch perform error checking on an incoming frame?

Begins the forwarding process after the destination MAC address of an incoming frame and the egress port has been determined.

How does cut-through-method work?

Makes a forwarding decision on a frame after it has received the entire frame and then checked the frame for errors.

How does store-and-forward method work?

It is used in High-speed searching applications and is populated as switches learns the relationship of ports to devices.

How does the CAM get populated?

The switch can look past the first 14 bytes of the frame and look at the 40 bytes in order to perform more sophisticated functions related to IPv4 layers 3 and 4

How does todays MAC controllers and ASICs switch use its cut-through method to quickly look at its frame headers to analyze its filtering purposes?

Typically 5 Minutes.

How long is a MAC Address kept in the table? (Aging Timer)

It contains multiple MAC addresses for a single port connected to the other switches.

In networks with multiple interconnected switches, what does the MAC address table do?

High Port Density Large Frame Buffers Port Speed Fast Internal Switching Low per-port cost

What characteristics help alleviate network congestion on switches?

A router

What device separates a broadcast domain?

The switch adds the source MAC address of the frame and the port where the frame was received to the MAC address table.

What does a switch do when the destination device responds?

It floods the frame to all ports, except the ingress port.

What does a switch do with a broadcast MAC address or a address not in the MAC table?

The switch forwards the frame out all ports (Flooding) except for the ingress port of the frame.

What does a switch do with a incoming frame that is not found in the MAC address table?

Cut-through switching method will not drop most invalid frames and are forwarded to other segments of the network. This can have a negative impact on bandwidth; thus, clogging up bandwidth with damaged and invalid frames.

What happens if there is a high error rate (invalid frames) in the network?

Application-specific integrated circuit.

What is ASIC?

Having fast internal forwarding capabilities allows high performance. The method that is used may be a fast internal bus or shared memory, which affects the overall performance of the switch.

What is Fast internal switching?

High-performance computing: is the use of parallel processing for running advanced application programs efficiently, reliably and quickly.

What is HPC?

Switches have high-port densities: 24- and 48-port switches are often just 1 rack unit (1.75 inches) in height and operate at speeds of 100 Mb/s, 1 Gb/s, and 10 Gb/s. Large enterprise switches may support many hundreds of ports.

What is High Port Density?

Switches provide high-port density at a lower cost. For this reason, LAN switches can accommodate network designs featuring fewer users per segment, therefore, increasing the average available bandwidth per user.

What is Low per-port cost?

Public Switched Telephone Network

What is PSTN?

The switch doesn't have to wait for the frame to enter the ingress port before making it forwarding decision. (Doesn't have to look up the destination MAC address of the frame in its MAC address table)

What is Rapid Frame Forwarding?

is an innovative feature that aggregates all of the available power in a stack of switches and manages it as one common power pool for the entire stack.

What is StackPower?

is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments.

What is a Broadcast Domain?

aggregating Layer 3 routing boundaries

What is a basic function of the Cisco Borderless Architecture distribution layer?

Are network segments that share the same bandwidth between devices. Because, two or more devices within that segment try to communicate at the same time, collision may occur.

What is a collision domain?

Is a modified cut-through switching that waits for the switch collision window to pass before forwarding the frame. -Each frame will be checked into the data field to make sure no fragmentation has occurred. -Provides better error checking than cut-through, with practically no increase in latency.

What is fragment free?

The ability to store more received frames before having to start dropping them is useful, particularly when there may be congested ports to servers or other parts of the network.

What is large frame buffers?

It is when you divide a network into segment and reduce the number of devices that compete for bandwidth. Which creates a new collision domain. More bandwidth is available to the devices on a segment, and collisions in one collision domain do not interfere with the other segments.

What is microsegmentation?

Depending on the cost of a switch, it may be possible to support a mixture of speeds. Ports of 100 Mb/s, and 1 or 10 Gb/s are common (100 Gb/s is also possible).

What is port speed?

Consists of all devices on the LAN that receive broadcast frames from a host.

What is the MAC broadcast domain?

It is the ability of the switch to start forwarding a frame earlier than store-and-forward switching.

What is the advantage to cut-through switching vs store-and-forward switching?

MAC broadcast domain

What is the layer 2 broadcast referred to as?

Ingress Port and Destination address

What is the two criteria that switches use when making a forwarding decision.

1.Hierarchical- Facilitates understanding the role of each device at every tier, simplifies deployment, operation, and management, and reduces fault domains at every tier. 2.Modularity- Allows seamless network expansion and integrated service enablement on an on-demand basis. 3.Resiliency- Satisfies user expectations for keeping the network always on. 4.Flexibility- Allows intelligent traffic load sharing by using all network resources

What principles is Cisco Borderless Architecture access layer built upon?

Full-duplex connections

Which connection increases LAN network performance and is required for 1 Gb/s Ethernet speeds or higher?

Fragment Free Fragment free is- -Is a modified cut-through switching that waits for the switch collision window to pass before forwarding the frame. -Each frame will be checked into the data field to make sure no fragmentation has occurred. -Provides better error checking than cut-through, with practically no increase in latency.

Which method is better at error checking? Cut-through method or Fragment Free?

Rapid frame forwarding and fragment free.

What are the primary characteristics of cut-through switching?

Error Checking and Automatic buffering

What are the two primary characteristics that store-and-forward does that distinguishes itself from cut-through.

Layer 2

At what layer does the store-and-forward method forward data frames?

Modular

Daisy-chain switches with high-bandwidth throughput.

No

Do switches filter broadcast frames?

Store-and-Forward

Store-and Forward or Cut-Through? A great method to use to conserve bandwidth on your network?

Store-and-Forward

Store-and Forward or Cut-Through? Buffers Frames until the full frame has been received by the switch?

Store-and-Forward

Store-and Forward or Cut-Through? Checks the frame for errors before releasing it out of its switch ports if the full frame was not received, the switch discards it?

Cut-Through

Store-and Forward or Cut-Through? No error checking on frames is performed by the switch before releasing the frame out of its port?

Cut-Through

Store-and Forward or Cut-Through? The destination Network Interface Card (NIC) discards any incomplete frames using this frame forwarding method?

Cut-Through

Store-and Forward or Cut-Through? The faster switching method, but may produce more errors in data integrity therefore, more bandwidth may be consumed.

Fixed Configuration

Switches with pre-set features or options.

Stackable

Switches: Affected by the number of interfaces, features and expandability.

Power

Switches: It is now common to power access points, IP phones, and even compact switches using Power over Ethernet (PoE). In addition to PoE considerations, some chassis-based switches support redundant power supplies. Redundancy through PoE.

Port Density

Switches: Network switches must support the appropriate number of devices on the network. Affected by the number of network devices to support.

Price

Switches: Switches with adjustable switching line/port cards.

Frame Buffers

Switches: The ability of the switch to store frames is important in a network where there may be congested ports to servers or other areas of the network. The capacity to store frames in the cache.

Cost

Switches: The cost of a switch will depend on the number and speed of the interfaces, supported features, and expansion capability.

Scalability

Switches: The number of users on a network typically grows over time; therefore, the switch should provide the opportunity for growth. Ability to adjust to growth of network users.

Port Speed

Switches: The speed of the network connection is of primary concern to end users. How fast the interfaces will process network data.

Reliability

Switches: The switch should provide continuous access to the network. Continuous access to the network.

It is used to provide flexibility to support any mix of Ethernet speeds. For example, handling an incoming frame traveling into a 100 Mb/s Ethernet port that must be sent out a 1 Gb/s interface would require using the store-and-forward method. With any mismatch in speeds between the ingress and egress ports, the switch stores the entire frame in a buffer, computes the FCS check, forwards it to the egress port buffer and then sends it.

Switches: What is automatic buffering?

Sites between the access and core layers and provides a fault tolerance infrastructure that ensures connectivity.

Switches: What is the Distribution Layer?