P2. Modules 1-4 Switching Concepts, VLANs, and InterVLAN Routing Flashcards
Which two terms are associated with frames entering or leaving an interface?
Ingress : Entering the interface
Egress : Exiting the interface
How does switching work in networking?
The decision how a switch forwards traffic is made based on the flow of that traffic.
A LAN switch maintain a table that is referenced when forwarding traffic through the switch.
How does the switch MAC address table work? What are they used for?
A switch is made up of an integrated circuit and the accompanying software that controls the data paths through the switch.
And to transmit a frame, the switch needs to know which port it should go to. It does this by learning which device is on each port and then building a MAC address table which is stored in CAM.
What is the Learn and Forward method?
- Learn- Examines the source address
Adds the source MAC if not in the table.
Resets the time out setting it back to 5 minutes if the source is in the table. - Forward - Examines Destination address
If the destination MAC is in the MAC address table it is forwarded out the specified port.
If a destination MAC is not in the table, it is flooded out all interfaces except the one it was received.
Which forwarding methods does the switch have?
Store and forward switching: Receives the entire frame and ensures the frame is valid. Store-and-forward switching is Cisco’s preferred switching method.
Cut-through switching: Forwards the frame immediately after determining the destination MAC address and the egress port.
Which two primary characteristics does Store-and-Forward switching have?
Error checking: The switch will check the Frame Check Sequence (FCS) for CRC errors. Bad frames will be discarded
Buffering: The ingress interface will buffer the frame while it checks the FCS. This also allows the switch to adjust to a potential difference in speeds between the ingress and egress ports.
Which characteristics does the Cut-Through switching have?
Cut-through forwards the frame immediately after determining the destination MAC.
A fragment-free method with checking the destination and ensuring that the frame is at least 64 bytes to eliminate runts.
Concept of Cut-Through switching:
Is appropriate for switches needing latency to be under 10 microseconds
Does not check the FCS(FRAME CHECK SEQUENCE), so it can propagate errors
It May lead to bandwidth issues if the switch propagates to many errors
Cannot support ports with different speeds going from ingress to egress.
What is a collision domain, and what makes them disappear?
The network segments that share the same bandwidth between devices(half-duplex) are known as collision domains. When two or more devices within the same collision domain try to communicate at the same time, a collision will occur.
Switches eliminate collision domains and reduce congestion.
Full duplex eliminates collision domains
What is a broadcast domain? What can divide a layer 2 broadcast domain? And how can we expand it?
A collection of interconnected switches form a single broadcast domain, which extends across all Leyers 1 or layer 2 devices on a LAN. Only a router can break the broadcast domain.
Increasing devices at layer 1 or layer 2 will cause the broadcast domain to expand.
What happens when a layer 2 switch receives a broadcast domain? What happens if there are too many broadcasts?
The broadcast will flood it out all interfaces except for the ingress interface, if there are too many broadcasts it can cause congestion and poor network performance.
Which 4 features on the switch alleviate congestion?
Fast Port Speeds: Depending on the model, switches may have up to 100Gbps port speeds.
Fast Internal Switching: This uses a fast internal bus or shared memory to improve performance.
Large Frame Buffers This allows for temporary storage while processing large quantities of
frames.
High Port Density This provides many ports for devices to be connected to LAN with less cost.
This also provides for more local traffic with less congestion.
What are LAN and VLAN?
LAN: local area network; all components are
physically connected
VLAN Virtual LAN
A VLAN is a logical partition of a L2 network where logical connections between devices form a virtual network irrespective of user/device location. A broadcast domain spanning over multiple physical LANs
What are the 7 feature and/or benefits of VLAN?
Segmentation of devices on the same switch
Better organized networks based on requirements and resources (faculty vs students)
Isolation of broadcast, multicast and unicast in individual VLAN.
Dedicated Ip address range for each VLAN
Smaller broadcast domains = better performance, less waster BW
Extra security - only the same VLAN devices can communicate
Cost reduction (multiple VLAN per switch port)
What is a default VLAN?
○ All ports VLAN1 Default
○ Native VLAN is VLAN1 by default
○ Management VLAN is VLAN 1 by default
○ VLAN 1 cannot be renamed or deleted
Which ranges of VLAN do we have?
Normal Range VLAN 1 1-1005
Extended range VLAN 1006-4095
