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CCNP > Packet Forwarding > Flashcards

Packet Forwarding Flashcards

1
Q

What are the 7 layers of the OSI model.

A

Layer 7: Application Layer: Provides an interface from the application to the network by supplying a protocol that works with that application.

Layer 6: Presentation Layer: Negotiates the data formats, such as ASCII text, or images like jpeg.

Layer 5: Session Layer: Provides methods to group multiple bidirectional messages into a work flow for easier management and easier blackout of work if that work flow fail.

Layer 4: Transport layer: This layer focuses on data delivery between two host.

Layer 3: Network layer: this layer defines logical addressing, routing and route protocols used to learn routes.

Layer 2: data-Link layer: This layer defines the protocol that transmits the data over a particular type of physical network. For a example PPP, HDLC, Ethernet.

Layer 1: Physical layer: this layer defines the characteristics of the transmission on the wire. Such as pins, use of pins, electrical current, light modulation etc.

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2
Q

What is a MAC address.

A

A MAC address is a 48- bit address that is divided up into 6 octets in a hexadecimal format.

Example aa:bb:cc:dd:ff:gg

The first 3 octets are the OUI organizational unique identifier number assigned to that manufacturer. The last three octets are random numbers never to be duplicated.

The MAC address is used to forward traffic across a layer two boundary.

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3
Q

What is the broadcast MAC address and what dose it do.

A

The broadcast MAC address is all FF.FF.FF.FF.FF.FF

It’s used by protocols such as ARP and switches to flood a frame to all host on that network.

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4
Q

Forwarding network traffic across layer 2 uses what information.

A. Source Ip

B. Destination
IP

C. Source MAC address

D. Destination MAC address

A

Destination MAC address

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5
Q

What type of network device helps reduce the size of the collision domain.

A. Hub

B. Switch

C. Load balancer

D. Router

A

Switch

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6
Q

Forwarding traffic across a layer 3 uses what information.

A. Source Ip

B. Destination
Ip

C. Source MAC address

D. Destination MAC address

A

Destination IP

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7
Q

What type of device reduces the size of a broadcast domain.

A. Hub

B. Switch

C. Load balancer

D. Router

A

router

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8
Q

The _____ is also know as the MAC address table.

A. Adjacency table

B. CAM

C. TCAM

D. Routing table

A

CAM

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9
Q

What dose a VLAN do.

A

A virtual LAN (vlan) provides Logical segmentation of a switch by creating multiple broadcast domains on that switch. Network devices in one VLAN Can’t communicate with devices in a different VLAN On a layer 2 level that traffic has to be routed first.

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10
Q

Vlans add how many bits to a packet header, and what fields are add.

A

Vlans add a 32 bit field.

The tag protical identifier (TPID): this 16 bit field is set to 0x8100 to identify the packet as a 802.1Q packet.

Priority Code Point (PCP): this 3 bit field indicates the layer two QOS markings.

Drop eligible indicator (DEI): this 1 bit field indicates whether the packet can be dropped when there’s congestion.

VLAN identifier (VLAN ID): this 12 bit field specifies the VLAN # associated with the packet.

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11
Q

VLAN ID has only a 12 bit field how many unique vlans dose that allow.

A

The 12 bits allows for 4094 vlans. Which are.

Vlan 0 reserved for 802.1p traffic and cannot be modified or deleted.

Vlan 1 the default vlan and cannot be modified or deleted.

Vlan 2 to 1001 are normal range Vlans and can be modified, deleted, and add.

Vlan 1002 to 1005 are reserved and cannot be modified or deleted.

Vlan 1006 to 4094 are exited vlans and can be add, deleted, and modified.

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12
Q

What’s the configuration command to create a VLAN and name it

A

1 move to global configuration mode with the command : config T

2 create the vlan with the command: vlan 10

3 name the vlan: name pc

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13
Q

What’s the command to view vlans and their port assignment.

A

Show vlan

The optional key words provide the following information.

Show vlan brief: displays only the port to vlan mappings.

Show vlan summary: displays a count of vlans , vlans participating in VTP, and vlans that are in the extended range

Show vlan name:
Show vlan #
List the information for just that vlan.

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14
Q

What’s the configuration command to assign a port to a vlan.

A

1 move into the desired port # with the command: interface g0/1

Optional to set multiple ports to the same vlan us: interface range g0/1 - 5

2 set the switch port mode with : switchport mode access

3 set what vlan you want the port or port’s to participate in: switchport access vlan 10

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15
Q

What’s the command to configure a trunk.

A

1 config T

2 interface g0/1

3 switchport mode trunk

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16
Q

What is the default Vlan on a switch port.

A

Vlan 1

17
Q

What is the default native vlan on a trunk port .

A

The default number is vlan 1.

The purpose of the native vlan is to allow traffic to flow over a trunk port for devices that dont use tagged frames or dose not understand 802.1q tagging.

Traffic that is advertised or received on a trunk port without the 802.1q tag gets associated to the native vlan # the native Vlan must match on both sides of the trunk port.

18
Q

Explain what is ARP and how it works.

A

ARP is the Address Resolution Protocol.

The address resolution protocol (ARP) table provides a method of mapping Layer 3 Ip addresses to Layer 2 MAC addresses by storing the IP address of a host to its corresponding MAC address.

A host will send out a ARP request on its local LAN when it dose not have the address in it’s table. The ARP request will be a broadcast request using the local host Mac and all Fs MAC for the destination.
The packet will contain the destination host IP but the MAC address field will be all 0s. The host with that Ip will respond and to the request by filling in it’s MAC address and send it back as a unicast packet.

19
Q

What’s the command to view the ARP table.

A

Show IP arp

The optional keywords make it possible to filter the information.

By a mac
Show IP arp aa.bb.cc.dd.ee.rr

By a IP address
Show IP arp 169.254.3.1

20
Q

What’s the command to assign a IP address to a routers interface.

A

Move into the desired interface
And attach the IP address.

Interface g0/1
IP address 10.10.10.10 255.255.255.0

21
Q

What’s the command to make a subinterface on a trunk port for a router to a switch.

A

Start by creating the subinterface for that vlan using a .vlan #
Then attach the vlan to that interface and the IP address

Interface g0/1.10
Encapsulation dot1q 10
IP address 10.10.10.2 255.255.255.0

22
Q

What is process switching.

A

Process switches also know as software switching, is a switching mechanism in which the CPU on a router is in charge of packet switching. This type of packet forwarding is slow and is typically only used when a packet can’t be switched using CEF.

23
Q

What is the job of IP_input

A

When a packet arrives the ip_input process is in charge of looking At the rounding table and the ARP table to find the next hop IP address the outgoing interface and the MAC address. It updates the destination Mac and source Mac. Decreases the TTL , recalculates the headers checksum, and send the packet on its way.

24
Q

What is SSO

A

Stateful switchover is a redundancy feature that allows a router with two Route processors to synchronize router configuration and and control plane state information. This is known as checkpointing . This allows redundancy if the main RP fails the second one can take over. To minimize disruption it’s best to enable NSF so the CEF tables are not cleared during a failure.

25
Q

What is CEF.

A

Cisco express forwarding CEF speeds up the routing process but keeping a copy of the routing table in it’s RIB. This allows CEF to forward packets with out the cpu being burdened.

26
Q

Centralized forwarding vs distributed forwarding architects

A

Centralized forwarding is slower then distributed. Centralized forwarding has the Route processor and the routing engine combined to make forwarding discussions.
Distributed uses routing engines separate from the RP.
So when a packet arrives on a line card it is processed right there instead of being sent to the RP

27
Q

What is a directed broadcast address.

A

This address is the last address in a subnet with the host portion being all 1’s aka 255 (example ) 10.1.1.255/24
When this address is used by a host every host on that local network will receive the traffic. this will not pass a layer 3 boundary routes will not forward broadcast.

28
Q

What is a local loopback address.

A

127.0.0.0 to 127.255.255.255
Is a loop back address used to test the host protocol stack. A host can send a message to itself. This is a non routed ip and cannot be used for configuration. IPv6 uses ::1 for its loopback

29
Q

What is a local broadcast.

A

The local broadcast is 255.255.255.255
This is used by a host when it doesn’t have a up address and doesn’t know the DHCP server address. It will send out a request using the 255 address

30
Q

What are the private IP address ranges for class A,B,C

A

Class A 10.0.0.0 - 10.255.255.255

Class B 172.16.00 - 172.31.255.255

Class C 192.0.0 - 192.168.255.255

31
Q

What is a link local address

A

169.254.0.0 range

This address is given out dynamically by the local host when it does not receive a IP from a DHCP server

32
Q

What’s the range of the class A adresses

A

1.0.0.0 - 126.255.255.255

0.0.0.0 is reserved
And 127.0.0.0 is used for loopbacks

33
Q

What is the range of class B address.es

A

128.0.0.0 - 191.255.255.255

34
Q

What is the range of class C addresses

A

192.0.0.0 - 223.255.255.255

35
Q

What is the range of class D addresses and what are they

A

224.0.0.0 - 229.255.255.255

Class D is multicast

CCNP (2 decks)

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