CCNP switch slides 6 Flashcards
source
http://quizlet.com/3373203/ccnp-switch-deck-6-flash-cards/
What are the 2 power over ethernet methods?
Cisco ILP and 802.3af
How many 802.3af power classes are there?
5 (0-4 with 4 being the highest)
What is the default 802.3af power class and its use?
if the switch or the powered device doesn’t suport power class discovery
How does 802.3af do power discovery?
sends a voltage across the receive pairs to detect a 25k ohm resistance
How does ILP do power discovery?
sends a test tone on the transmit pair. If a device is detected, CDP is used to narrow down the power class.
What ILP mode are all ports in by default?
auto mode
How does a Cisco IP phone connect upstream?
via an 802.1Q trunk or a single VLAN access port
What are the 2 choices for VLANs with IPT?
they must be carried over a voice VLAN (VVID) or over a regular data VLAN (ie. The native VLAN or the PVID)
How is the IPT 802.1 trunk negotiated?
Automatically using DTP and CDP
How does IPT behave when the voice VLAN is in vlan-id mode?
data goes over native vlan, voice goes over specified VLAN, voice QOS is 802.1p
How does IPT behave when the voice VLAN is in dot1p mode?
data goes over native vlan, voice goes over VLAN0, voice QOS is 802.1p
How does IPT behave when the voice VLAN is in untagged mode?
data and voice over native vlan, no QOS but still uses 802.1p trunk
How does IPT behave when the voce VLAN is in the default none mode?
data and voice over native vlan no QOS and no 802.1p trunk
What is latency?
the total delay from start to finish
What is jitter?
variation in delay
What are the three basic types of QOS?
best effort delivery, integrated services model, and differentiated services model
What is best effort delivery QOS?
switches make an effort to move packets as quickly as possible
What is integrated services model QOS?
A path is pre-arranged for priority along the complete path from source to destination using the RSVP protocol.
What is differentiated services model QOS?
Each network device handles packets individually with no advance reservations
What method of QOS does voice traffic use most frequently?
differentiated services
How does an L2 switch do QOS?
an L2 switch can only forward frames best effort unless going across a trunk
How does 802.1q handle COS?
The frame tag includes a 3 bit COS value from 0 (low) to 7 (high). Native vlans are untagged so no COS
How does ISL handle COS?
The frame tag contains a 3 but portion tagged from 0 (low) to 7 (high)
How does L3 QOS classification happen?
The TOS field in the header is used. 2 methods 3 bits or 6 bits
What is DSCP?
Differentiated services code point
How does DSCP handle IP precedence?
5 classes with 3 drop precedences
What is DSCP codepoint EF(46)?
Critical…used most often for IPT
What is DSCP codepoint AF41(34)?
Flash override (class 4)
What is DSCP codepoint AF31(26)?
Flash (class 3)
What is DSCP codepoint AF21(18)?
immediate (class 2)
What is DSCP codepoint AF11(10)?
priority (class 1)
What is a QoS trust boundary?
The point at which a switch decides to trust incoming Qos. Usually at boundary with ISP
How is a QoS trust bondary configured?
Every switch and router in a network must be configured with appropriate QoS features and policies
Where is the QoS trust boundary usually configured on an IP phone?
Usually QoS from VOIP but not PC dataa
What are the 4 steps to extend QoS trust?
1- enable qos, 2-define qos parameters to be trusted, 3-make trust conditional, 4-instruct IP phone how to extnd boundary
For QoS, switch uplinks should always be considered as ____ _____?
trusted ports
How much BW does a PSTN connection use?
63 kbps
How much BW does a voip connection use?
12 kbps with headers and compression
How do Cisco IP phones communicate with the CCM?
with the skinny protocol
What does the skinny protocol do?
transmits keystrokes from phone and commands from CCM
How do IP phones communicate with each other?
Once the CCM gives them the parameters, they use RTP
What is RTP?
Real-time Transport Protocol
What is the standard for WLANs?
802.11
What duplex setting does 802.11 use and why?
half because transmitting and receiving stations use the same frequency
What feedback mechanism does wireless use?
when a wireless station transmits a frame, the receiving one must send an ack
If a wireless station needs to transmit and no other device is transmitting, what happens?
The station can transmit immediately and wait for an ack
If a wireless station needs to transmit and another device is transmitting, what happens?
The station must wait until the frame in progress has completed, then wait a random amount of time before transmitting
What is the DIFS?
The DCF interframe space- the random backoff time before a wireless set can transmit
What is the duration time in a wireless frame?
Each frame transmits its expected duration time
What is DCF?
Distributed coordinion function - the use of timers to prevent wireless collisions
What is a service set?
A group of wireless devices that share a common SSID
What is an IBSS?
the wireless clients communicate directly with no other means of connectivity such as a WAP
What is a BSS?
Using a single WAP to centralize access and control over a group of wireless devices.
What must be in common for a BSS to form?
matching SSID, compatible data rate, authentication credentials
What is an ESS?
When the AP uplinks to an Ethernet network.
How are multiple VLANs mapped to multiple SSIDs?
By using a trunk link
What is a cell?
An AP’s coverage area
What must you be sure of if AP cells overlap?
That they aren’t using the same frequencies.
What is layer 2 roaming?
If the client maintains the same IP address as it roams between Aps. All must have same VLAN, SSID, and subnet
What is layer 3 roaming?
When a client roams between Aps in different subnets
What is a microcell?
When the size of a cell is intentionally reduced
What is an autonomous mode AP?
When each AP stands alone within the larger network.
What functions does a LAP perform?
Real-time functions such as beacons and probes, encryption and interactions with the client at L2
What functions does a WLC perform?
Control functions
How does an LAP bind with a WLC?
by brining up a tunnel between them to carry 802.11 related messages and client data.
Does a WLC and a LAP need to be on the same subnet?
No
What 2 tunnelling mechanisms do the LAP and WLC use to communicate?
LWAPP (Cisco proprietary) and CAP-WAP (standards based)
How many tunnels exist between the LAP and WLC?
2 - one for control messages and one for data
How does a LAP and a WLC authenticate between each other?
using digital certificates
What are the 5 steps a LAP uses to establish communication with a WLC?
1-LAP gets a DHCP address, 2-LAP learns IP of available WLC, 3-LAP sends a join request to WLC and receives join reply, 4-WLC sends code image, if necessary, 5-Tunnels are created
How does a DHCP server send WLC addresses?
Option 43
What does a LAP do if it loses communication with it’s WLC?
Reboots and searches for a new WLC
How does a WLC hand off a client’s association to another WLC?
using a mobility exchange message
How is a WLC handoff handled when the WLCs are in different subnets?
by using an Ether-IP tunnel
What is a wireless mobility group?
A client can roam to any WLC as long as it stays in a mobility group
How should the switch port to which an autonomous AP be configured?
trunk
How should the switch port to which a LAP be configured?
access
At what layer should the WLC be connected?
distribution
How should the switch port to which a WLC be configured?
trunk
If the WLC connects to an Etherchannel, how should the channel be configured and why?
they should be an unconditional Etherchannel because the WLC can’t negotiate a channel.
How much overlap should WAPs have?
10-15%
How much overlap should a wireless repeater have?
roughly 50%
What can cause a wireless client to switch between Aps?
missed beacons, dropped packets (max retry), weak signal (data rate switches down), an AP periodicallytries to find a stronger signal
What are the 3 unlicensed frequencies?
900 MHz, 2.4Ghz, and 5-6GHz
802.11b
1,2,5.5 and 11 Mbps, Channels 1/6/11, 2.4Ghz
802.11g
Compatible with 802.11b, up to 54Mbps in 12 data rates, 3 channels, 2.4Ghz
802.11a
up to 54Mbps, not cross-compatible, 12 to 23 clean channels, 5.8 Ghz
WEP encryption
weak key rotation
EAP encryption
dynamic WEP keys that change periodically
WPA encryption
interim solution, uses same hardware as WEP, but uses TKIP encryption
WPA2 encryption
needs hardware upgrade over WEP, uses AES encryption
