Packet Switching Flashcards
What are the 7 layers of the OSI model? Please Do Not Throw Sausage Pizza Away
1) Physical - bits
2) Data Link (node to node transfer) - frames
3) Network (routing) - packets
4) Transport (UDP - datagrams /TCP - segments)
5) Session - data
6) Presentation - data
7) Application - data
What is a CAM table?
Content Addressable Memory - table is a data structure used by network switches to store information about MAC (Media Access Control) addresses and the physical switch ports associated with them (AKA MAC ADDRESS TABLE)
TCAM table
Ternary Content Addressable Memory (uses NVRAM) - allows for high-speed access to routing and access control information
What is a PDU
Protocol Data Unit - refers to the specific unit of data relevant to each layer in the OSI model. Each OSI layer has its own PDU type, encapsulating data with the necessary headers and/or trailers needed for that layer’s function before passing it to the next layer.
Displaying the CAM table aging time
SwitchA#show mac—address—table aging—time
Configuring the CAM table aging time
SwitchA (config) #mac—address—table aging—time 1200
Displaying all MAC addresses the switch has learned
SwitchA#show mac—address—table
Displaying MAC addresses learned through a specific switch port
SwitchA#show mac—address—table interface fastethernet 0/1
Displaying the CAM table entry for a specific MAC address
SwitchA#show mac—address—table address AF—D3—C0 43—FB—85
Which OSI model layer do “bits” belong to?
Layer1, Physical
Which OSI model layer do “frames” belong to?
Layer 2, Data Link
Which OSI model layer do “packets” belong to?
Layer 3, Network
Which OSI model layer do “segments (in TCP)” belong to?
Layer 4, Transport
Which OSI model layer do “datagrams (in TCP)” belong to?
Layer 4, Transport
Which OSI model layer do “session messages (or data) “ belong to?
Layer 5, Session
What is an ASIC
Application-Specific Integrated Circuits, specialized circuits for processing network data
Packet Switching: process switching
Slowest of the three packet switching methods, uses software and CPU of the switch, used for complex methods like NAT and encryption
Packet Switching: fast switching
“route caching” uses CPU only for first part
Packet Switching: CEF switching
Cisco Express Forwarding, AKA topology-based switching
To enable fast switching, issue… command at the global config mode
ip route-cache
To disable fast switching, issue… command at the global config mode
no ip route-cache
display the fast -switching cache
Router#show ip cache
display the RIB
Router#show ip route
display the FIB
Router#show ip cef
show the CEF adjacency table
Router#show adjacency
show the arp table
Router#show ip arp
configure CEF load balancing per packet
router(config-if)#ip load-sharing per-packet
configure CEF load balancing per packet
router(config-if)#ip load-sharing per-destination
configure the CEF load balancing algorythm
Router(config)#ip cef load-sharing algorythm xxxxxxxx
what are the 4 types of CEF LB algorythms?
origional
universal (default)
tunnel
include-ports (layer 4)
What are the QoS parameters for Layer 2 ?
802.1p CoS , 802.11 TID
QoS: what is COS?
Class of Service, Layer 2, 3-bit field in the VLAN (802.1Q),
QoS: what is ToS
Type of Service
What are the QoS parameters for Layer 3 ?
IP ToS , DSCP
QoS: DSCP
Differentiated Services CodePoint use 6 left most bits 2^6 or 64 possible classifications, Layer 3
QoS: IP precedence
2^6 possible classifications
QoS: PHB (DSCP)
Per Hop Bevaviors (21 labeled classifications out of 64) ITF created these. if the binary doesnt end in “0” it is not a class the ITF set up
PHB - default (DSCP)
000000 or 0
QoS: PHB - Expidited Forwarding (EF) (DSCP)
101110 or 46 (backwards compatible with IP precendence
QoS: DCSP Assured Forwarding (AF) values
4 classes, but the first three binarys match the old IP precedence
QoS: Random Early Detection, RED
QoS - Explicit Congestion Notification (ECN)
The routers politly asking teh source to slow down bits 7 and 8 - 00 “rtr does not speak ECN”, a single one “rtr speaks ECN”, both bits are 1’s, rtr “speaks and is experiencing congestion”
QoS: CB-WFQ
Class-Based Weighted Fair Queueing
QoS What is Shaping
Polite, delays, queues (works with bits)
QoS What is Policing
the Nazi that drops traffic (works with bytes)
QoS: What is MQC
Modular Quality of Service, Command Line Interface
QoS: What are Class Maps
Define and classify traffic types (Cisco recommends 11 or less classes)
QoS: What are Policy Maps
Specify what QoS actions to apply to each class (e.g., bandwidth allocation, priority)
QoS: What are Service Policies
Apply the policy map to an interface.
Qos: what is the command to create a Class Map?
R1(config)#class-map match-any [CLASSNAME] –> match protocol [PROTOCOL]
Qos: what is the command to show the class maps?
R1(config)#do show class-map
Qos: what is the command to create a policy map?
policy-map[MAPNAME] –> class [CLASSNAME] –> [ACTION]
QoS: what are the steps to setting up QoS/MQC?
setup classes, setup policies, apply to the interface
QoS: what is the command to apply a policy to the interface?
R1(config-if)#service-policy output [POLICY NAME]
QoS: powerful command to show a policy applied on an int
R1#show policy-map interface [INTERFACE NAME]
QoS: What are the three versions of AutoQoS?
Router-based AutoQoS VoIP, Switch-based AutoQoS VoIP, & Router-based AutoQoS Enterprise
QoS: Router-based AutoQoS VoIP only works on Ethernet ports
False: is only works on WAN circuits
QoS: what is the command to implement router based auto QoS?
R1(config-if)# auto qos voip
QoS: what is created using router based auto QoS?
Class maps referring to an extended ACL
An ACL that matches voice traffic,
A policy map
QoS: command to start the autoQoS ENterprise process?
R1(config-if)#auto discover qos
QoS: What are the steps of AutoQos Enterprise?
discovery (wait 2-3 days), look for what was discovered, apply what was discoered.
QoS: how to view what auto QoS enterprise has discovered
R1#show auto discovery qos interface [INT NAME]
QoS: how to apply what was discovered using auto qos enterprise
R1(config-if)# auto qos
QoS: What are the 4 wifi access categories?
Voice (AC_VO)
Video (AC_VI)
Best Effort (AC_BE)
Background (AC_BK)
WMM QoS IEEE 802.1P categories mapped to
QOS: What is the the BE class?
Best Effort, low priority
QOS: What is the the EF class?
Expedited Forwarding, highest class
QOS: What is the the AF class?
Assurd Forwarding, AF Classes (1 to 4): Higher class numbers indicate higher priority within the AF class hierarchy.
QoS: What are the 12 possible DSCP values for AF
QoS: What are the category, CoS, and DSCP values in wireless QoS?
QoS: what are the 4 basic queueing mecahnisms in congestion management?
FIFO (first in first out)
PQ (priority queueing)
CQ (custom queueing)
WFQ (Weighted Fair Queueing)
QoS: FIFO (first in first out)
default, basically nothing
QoS: PQ (priority queueing)
4 queues, guarantees high priority is first but can cause lower priority to be starved
QoS: CQ (custom queueing)
16 queues,
QoS: WFQ (weighted fair queueing)
256 queues, round robinsdistributes bandwidth based on class
QoS: LFI (Link Fragmentation and Interleaving)
breaks up large packets so that small, jitter sensitive packets don’t have to wait so long)
QoS: what are the 4 scheduling mechanisms?
Strict Priority
Round Robin
Weighted fair
QoS: congestion avoidance, tail drop
drops off the last packets to open up more space in the queue
QoS: congestion avoidence, RED (rendom early detection)
a congestion avoidance method that can avoid global synchronization
QoS: congestion avaoidence, what is WRED
Ciscos version of RED, Weighted Random Early Detection, probability of a packet getting discarded is dependent on its IP precedence
What are the three steps to setting up QoS?
Define the CLASS MAP
Define the POLICY MAP
LINK the Policy Map to the Interface
