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CCNP 350-401 Encor > Chapter 1 Packet Forwarding > Flashcards

Chapter 1 Packet Forwarding Flashcards

1
Q

What is unknown Unicast flooding?

A

When a packet contains a destination MAC address that is not in the switch’s MAC address table. The switch forwards the packet to every switch port.

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2
Q

What is a VLAN?

A

VLAN provide logical segmentation by creating multiple broadcast domains on the same network switch.

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3
Q

What are the four fields that are added to the 802.1Q packet header?

A
  1. Tag protocol identifier (TPID): this is a 16 bit field set to 0x8100 to identify the packet as an 802.1Q.
  2. Priority code point (PCP): This 3-bit field indicates a class of service (CoS) as part of layer 2 QoS between switches.
  3. Drop eligible indicator (DEI): This is 1-bit field indicates whether the packet can be dropped when there is a bandwidth contention.
  4. VLAN identifier (VLAN ID): This 12-bit field specifies the VLAN associated with a network packet.
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4
Q

How many unique VLANs can be created from the 12bits of VLAN ID?

A

4094 Unique VLANs.

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5
Q

What is VLAN 0?

A

It is reserved for 802.1P traffic and cannot be modified or deleted.

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6
Q

What is VLAN 1 ?

A

It is the default VLAN. It cannot be modified or deleted.

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7
Q

What are the normal VLAN range?

A

VLANs 2 to 1001. They can be added, deleted or modified as necessary.

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8
Q

What are the reserved VLAN?

A

VLANs 2 to 1005 are reserved and cannot be deleted.

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9
Q

What are the extended VLANs?

A

VLAN 1006 to 4094. They can be added, modified and deleted.

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10
Q

What is an Access port?

A

Access port is designed to access only one VLAN.

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11
Q

What tag is not included on an access port?

A

The 802.1Q tags are not included on packets transmitted or received on access ports.

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12
Q

What is a Trunk port?

A

Trunk ports can carry multiple VLANs between a switch and another switch.

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13
Q

What is a Native VLAN?

A

Any traffic that is advertised or received on a trunk port without the 802.1Q VLAN tag is associated to the native VLAN.

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14
Q

What is the purpose of MAC address Table?

A

It is responsible for identifying the switch ports and VLANs with which a device is associated.

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15
Q

How does switches build MAC address table?

A

Switches build MAC address table by examining the source MAC address for traffic that it receives.

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16
Q

Where does MAC address table resides?

A

MAC address tables resides in CAM. The CAM uses high speed memory that is faster than typical computer RAM due to its search techniques.

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17
Q

What are the two main methods of layer 3 forwarding?

A
  1. Forwarding traffic to devices on the same subnet.

2. Forwarding traffic to devices on a different subnet.

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18
Q

What is the purpose of ARP table?

A

ARP table provides a method of mapping Layer 3 IP Address to Layer 2 MAC address by storing the IP of a host and it’s corresponding MAC address.

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19
Q

What is contained in the ARP table?

A

ARP table contains entries for remote devices that the host has communicated with recently and are on the same IP network segment.

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20
Q

Which commands route packets between VLANs?

A

SW1# Configure Terminal
SW1(config)# interface vlan 10
SW1(config-if)# IP address 10.10.10.1 255.255.255.0
SW1(config-if)# ipv6 address 2001:db8:10::1/64
SW1(config-if)# no shutdown

SW1(config-if)# interface VLAN 99
SW1(config-if)#Ip address 10.99.99.1 255.255.255.0
SW1(config-if)#ipv6 address 2001:db8:99::1/64
SW1(config-if)# no shutdown

21
Q

What is a process switching?

A

Process switching also referred to as software switching or slow path, is a switching mechanism in which the general purpose CPU on a router is in charge of packet switching.

22
Q

Types of packets that require soft handling?

A
  1. Packets sourced or destined to the router( using control traffic or routing protocols)
  2. Packets that are too complex for the hardware to handle ( that is IP packets with IP options)
  3. Packets that require extra information that is not currently known ( for example ARP)
23
Q

What is the difference between software and hardware switching?

A

Software switching is significantly slower than switching done in hardware.

24
Q

How is the routing table built?

A

The routing table also known as Routing Information Base (RIB), is built from information obtained from DYNAMIC routing protocols, DIRECTLY connected and STATIC routes.

25
Q

What is Cisco Express Forwarding (CEF)?

A

CEF is a Cisco proprietary default switching mechanism on most Cisco platforms that do all their packet switching using the general-purpose CPU.

26
Q

What is Ternary Content Addressable Memory (TCAM)?

A

TCAM allows for the matching and evaluation of a packet on more than one field. It is the extension of the CAM architecture but enhanced to allow for upper- layer processing.

27
Q

What three results does TCAM search provide?

A

Zero (0) for true

One (1) for false

X for do not care

28
Q

Why does TCAM operates on hardware ?

A

To provide faster processing and scalability than process switching. This allows for some features like ACL to process at the same speed regardless of whether there 10 entries or 500.

29
Q

What is a centralised forwarding?

A

When a Route Processor(RP) engine is equipped with a forwarding engine so that it can make all the packet switching decisions.

30
Q

What is a distributed architecture?

A

Distributed architecture is when a line card is equipped with forwarding engines so that they can make packet switching decisions without the intervention of Route Processor.

31
Q

What are the components of software CEF?

A
  1. Forwarding Information Base: The FIB is built directly from the routing table and contains the next-hop IP address for each destination in the network.
  2. Adjacency Table: The adjacency table, also known as the Adjacency Information Base, Contains the directly connected next-hop IP addresses and their corresponding next-hop MAC addresses. It is populated with data from the ARP table or other Layer 2 protocol tables.
32
Q

What is a TTL used for?

A

The TTL is a layer 3 loop prevention mechanism that reduces a packets TTL field by 1 for every layer 3 hop.

If a router received a packet with a TTL of 0, the packet is discarded.

33
Q

What is a route processor (RP)?

A

RP is responsible for learning the network topology and building the route table (RIB)

34
Q

What is a Stateful Switchover?

A

SSO is a redundancy feature that allows a Cisco router with two RPs to synchronise router configuration and control plane state information.

35
Q

What is checkpointing?

A

The process of mirroring information between two RPs.

36
Q

CEF is composed of which components?

A
  1. Forward Information Base

2. Adjacency Table

37
Q

What are the characteristics of a layer 2 switch access port?

A
  1. Access mode will is the default operating mode for a port on a layer 2 switch.
  2. An access port is associated with a single VLAN.
38
Q

Which packet forwarding process uses ternary content addressable memory (TCAM)?

A

Hardware CEF

39
Q

What is a feature of a Cisco Switch SVI?

A

An SVI is configured by setting it as a VLAN interface.

40
Q

Which Cisco router component performs process switching of packets?

A

The general-purpose CPU.

41
Q

What is the difference between a routed switch port and a trunk port on a multilayer switch?

A

A router port is assigned an IP address.

42
Q

What would be the source of the entries in the ARP table of a particular IPv4 host?

A

Devices that the host has communicated with recently that are on the same IP Network segment.

43
Q

Which is the correct description of a native VLAN on a Cisco switch?

A

The VLAN that contains any untagged network traffic on a trunk port.

44
Q

Which router memory component is used by CEF to make packet forwarding decisions?

A

Forwarding Information Base(FIB)

45
Q

Where does a Cisco switch store the MAC address table entries?

A

CAM

46
Q

Which CEF component enables multiple actions to be performed in addition to allowing or dropping traffic?

A

TCAM

47
Q

What is a feature of virtual LANs ?

A

Logical segmentation is provided by creating multiple broadcast domains on a single switch.

48
Q

What are two characteristics of a layer 2 Ethernet trunk ports?

A
  1. Trunk ports carry multiple VLANS

2. Trunk ports connect a switch to other switches or other network devices.

CCNP 350-401 Encor (5 decks)

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