Block 7 Flashcards
Data link layer addresses are also referred to as (4 others)
Physical, hardware machine or MAC address
What defines how devices are addressed at the data link layer
Physical addressing
What consists of the data link layer specifications that often define how devices are to be physically and logically connected?
Network topology
Error detection uses CRC or FCS to detect errors in transmission. What layers are responsible for the actual error correction or request or request for transmission of a frame?
Higher layers
What reorders frames that are received out of sequence?
Sequencing of data frames
What moderates the transmission of data so that the receiving device is not overwhelmed with more than it can handle at one tim?
Flow control
Switches primary method of flow control is?
Buffering
What connects multiple network segments at the data link layer of the OSI model?
Bridge
Layer 2 switching is very efficient because
No modification to packet
Only to frame encapsulation
And only when the data packet is passing through dissimilar media
Bridges are ___________ based and switches are __________ based
Software
Hardware
Bridges have a ________ spanning tree control and switches have a _________ spanning tree control
Limited
Advanced
How many ports do switches have?
Hundreds
How many ports do bridges have?
16
A physical or logical network segment in which data packets can collide with each other
Collision domain
__________ reduces the chances of this happening by preventing more than one device from accessing the Collision domain at the same time, but collisions can still occur.
Ethernet 802.3 CSMA/CD
All network segments connected by layer 1 devices exist on a ___________ collision domain.
Single
How many collision domains are on layer 2 devices ?
Each interface is a separate collision domain
A logical network segment defined by its router port
Broadcast domain
Devices physically connected to same media or layer 2 device will be on
Same broadcast domain
What do switches use to build and maintain MAC address tables ?
Application-specific integrated circuits (ASICs)
What do switches use to filter traffic?
MAC address from the host NIC
Layer 2 switches provide ?
Hardware-based bridging
Wire speed
Low latency
Low cost
Most common type of switches
Ethernet switches
3 major functions of layer 2 switches
Address learning
Forward/filter decision
Loop advance
3 methods of frame switching methods
Store and forward Cut through(real time) Fragment free(modified cut-through)
Where are the MAC address tables stored in the switches?
RAM
Most switches hold up to how many MAC address in their table?
8000
If a workstation does not talk for a period of time on the network chances are?
The MAC address has aged out (removed) from the table
What helps I preserve bandwidth I other network segments?
Frame filtering
In this Frame switching method the switch copies the entire frame into its buffers and computes the CRC.
*Best for error free but greatest amount of processing time?
Store-and-forward
Also called real time, in this frame switching method the LAN switch only copies the destination address onto it’s on board buffers.
*reduces latency because no error checks but fastest method
Cut-through
Also called modified cut-through, this frame switching method waits 64 bytes(collision window) to pass before forwarding.
*better error checking than cut-through mode with no increase in latency
Fragment free
If a packet has an error it almost always occurs within the first __________.
64 bytes
Why is it a good idea to use multiple (redundant) links between switches and multiple switches?
To avoid a single point of failure
If loop avoidance schemes are not put in place, the switches will flood broadcasts endlessly throughout and internetwork.
Broadcast storms
If a device receives multiple copies of the same frame because the frame can arrive from different segments at the same time what problem is occurring?
Multiple frame copies
One of biggest problems generating through an internetwork where loops occur within loops
Multiple loops
Use by layer 2 devices to stop network loops in networks that have more than one physical link to the same network
STP spanning tree protocol
An external component that allows you local direct access to the switch during configuration
Console port
And external component where you will connect your end devices such as your computers or printers.
Network interfaces
And internal component where the diagnostics and boot up routines are stored. the contents of this type of memory cannot be changed since they are burned in the chip.
Rom
Internal component that holds the Internet work operating system. this type of memory is similar to EEPROM.
Flash memory
I’m going to start up operation the iOS is copied from the ______memory into ram for execution.
Flash
This internal components type of memory is call nonvolatile memory. When Powers is removed from the switch the content of this memory will remain unchanged.
Used to store start -up config file
NVRAM
This type of memory is called volatile memory. when power is removed from the switch the content of this memory will be lost.
Ram
A logical grouping of network computers and resources connected to administratively defined ports on a layer 2 switch.
VLAN
This is also called a broadcast domain and all connected devices see all broadcast packets that are transmitted.
Flat network
What are VLAM benefits
(I)ncreased security
(N)o geographical barrier
(f)lexibility and scalability
(b)roadcast control
What are the two types of the VLAN port membership assignments
Dynamic and static
Which VLAN membership takes more work upfront but is easier to maintain
Dynamic VL AN
Which VLAN membership requires less work initially but is more time-consuming for an admin to maintain
Static VLAN
What are the two different link modes
Access link or trunk link
What allows Cisco switches to automatically negotiate with other Cisco devices when they connect
Dynamic trunking protocol
Switches without dynamic trunking protocol cannot negotiate and must be manually configured as
Access or truck link through static assignments
A link that is assigned to one VLAN
Access link
This link will carry traffic for all VLANs unless you specify otherwise
Trunk link
What is the minimum speed for Trunk link
100 Mbps
What are the two frame identification methods that Cisco supports
Inter-switch link (ISL)
IEEE 802.1q
What uniquely assigns a user defined ID to each frame also call frame tagging
Frame identification
VLAN frame identification places a ____________ in the header of each frame as it is forwarded through the switch fabric on Trunk links
Unique identifier
Cisco proprietary protocol that is a way of encapsulating a VLAN frame with an added headed and trailer.
ISL inter-switch link protocol
This process enables VLANs to be multiplexed over a trunk link through an external encapsulation method.
*external encapsulation method
ISL
An open source standard method of frame tagging .
*internal tagging method
IEEE 802.1q
A Cisco proprietary protocol that eases management of VLANs in an internetwork.
VLAN trunking protocol (VTP)
Allows for creation, addition, deletion of control within an administrative domain .
VTP
How many VTP domains do a switch belong to?
1
A switch shares VLAN information with other switches in
The same domain
What are the three modes a switch can operate in?
Server
Client
Transparent
A central point(management) for VLAN creation within a domain
Server
What mode receives information from a server and can forward received updates to other switches ?
Client
This mode does not partake on VTP domain but can still receive and forward VTP advertisements through trunk links
Transparent
What do VTP advertisements include?
Management domain name
Configuration revision #
VLANs
Parameters for each VLAN
If a client receives an advertisement that has a higher revision #, what will happen
It will overwrite the database in NVRAM with the database being advertised
If a switch was connected to another network it’s best to clear everything from its memory and then power-cycle it.
Reason?
So a high revision # will not overwrite the system
What provides consistent network availability when an outrage occurs for one link?
Spanning-tree protocol (STP)
A standardized protocol that provides a stable fault-tolerant loop free environment while selecting the fastest network path when redundant links exist with in a internetwork
STP
Which algorithm chooses one path on which to forward frames and places the other redundant links in blocking state to stop any network loops from occuring
Spanning-tree algorithm
What device will be the loop bridge?
The device with the lowest bridge ID
All ports on the root bridge are called __________ and are set to _________
Designated ports
Forwarding “meaning they will pass data@
After the root bridge is selected all other remaining switches become the ____________
Non-root bridge
What is the main device that other switches in the network will “key on” to set their ports to forwarding or blocking to establish a path
Root bridge
Later 2 devices with STP capability will exchange info using the ______________
Bridge protocol data units (BPDUs)
How many bytes is the bridge iD and what does it include
8 bytes and includes the default priority plus the MAC of the device
The default priority for all devices running the IEEE version of STP is?
32768
Root ports are in _______ mode and provide a constant connection to the root bridge from the non root bridge so advertisements and updates are received.
Forwarding
These ports are used to prevent loops. after a switch has determine the best path to the bridge all other ports are placed in the blocking state
Non designated port (blocked)
This occurs when bridges and switches have completed the transitions to either the forwarding or blocking state
Convergence
How long can convergence take up to
50 secs
How much data is forwarded doing convergence
None
By default what runs on all switch ports
Spanning tree protocol
whenever a New port is enable spanning tree goes through the following port states to get that port to be either forwarding or blocking
Blocking- will not forward frames
Listening- listens to make sure no loops before pass in frames
Learning -learns Mac addresses and builds tables
Forwarding- bridge port able to send and receive data …a port will never be placed in forward state unless there are no redundant links
What is use to speed up convergence on ports that are connected to workstations and servers or other devices that will not cause layer 2 loops
Spanning tree portfast
What are the three spanning tree protocol standards
CST common spanning tree
PVST Per-VLAN spanning tree
PVST + Per VLAN spanning Tree +
Also called mono spanning tree because it uses only one spanning tree instance regardless of the size of the later 2 networks or number of VLANs
CST common spamming trees
Cisco proprietary, uses ISL and runs a separate instance for each VLAN.
Smaller STP implementation and easier convergence
Per-VLAN spanning tree (PVST)
