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myCCNP Switch 300-115 > MultiLayerSwitch-General > Flashcards

MultiLayerSwitch-General Flashcards

1
Q

What does L3 switching allow you to avoid?

A

Router-on-a-stick. Reduces points of failure and saves bandwith.

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2
Q

What are the two flavors of Cisco’s catalyst switch-route software?

A

MLS (multilayer switching) and CES (Cisco express forwarding)

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3
Q

How does MLS work?

A

With route-caching. The first packet in a flow is routed by the switch processor, while the rest in the flow are sent through ASICs.

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4
Q

What does “packet flow” mean?

A

A unidirectional stream of packets to a single destination, all part of the same protocol.

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5
Q

What is more common, CEF or MLS?

A

CEF, and it’s newer.

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6
Q

What must be enabled for a switch to act as a default gateway?

A

IP routing.

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7
Q

What is a requirement for an SVI to be active?

A

It must be tagged/untagged on at least one port.

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8
Q

What does each layer 3 segment require to be utilized?

A

Some kind of route or routing protocol.

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9
Q

What command will enable a routed port?

A

From interface config, “no switchport”

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10
Q

How do IP addresses and MAC addresses change as a packet is moved through a network?

A

IP addresses (source and destination) stay the same, MAC adresses (source and destination) change at each hop.

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11
Q

What is a useful show command that displays the MAC Address Table?

A

Switch# show mac address-table <dynamic> <address></address></dynamic>

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12
Q

What is route caching?

A

The RP listens to a flow’s 1st packet for the dest. The SE listens to the packet and dest and puts a shortcut in the MSL cache. Netflow switching, route once, switch many

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13
Q

What is topology-based caching?

A

the topology is pre-populated by downloading the topology DB into the FIB and dynamically updated. Called Cisco Express Forwarding

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14
Q

What three decisions must be made after the switch processes the ingress queue?

A

Where to forward the frame, where it should be forwarded, and how. All happen simultaneously.

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15
Q

If a switch receives a frame and the source MAC is not in it’s forwarding table, what information will be stored about the new frame?

A

The MAC address, the switch port, and the VLAN on which it arrived.

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16
Q

In multilayer switching, what 4 specific decision are made simultaneously to forward data?

A

-The L2 forwarding table(CAM)-The L3 forwarding table(FIB)-Security ACLs.-QoS ACLs.

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17
Q

What are the two types of multilayer switching (MLS)?

A

-Route caching, basically route-once-switch-many.-Topology based, uses the layer-3 routing table (called FIB) to make a forwarding decision.

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18
Q

What is unknown unicast flooding?

A

When a switch receives a frame and the destination MAC is not in its forwarding table, it forwards the message (or floods) out all ports on the same VLAN as the source.

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19
Q

When multilayer switching, what information must be changed in the packet and frame, by the packet rewrite engine, before the data can be forwarded out a port?

A

The L2 source and destination MAC, the L3 TTL and L3 header checksum, and the L2 checksum.

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20
Q

In topology-based multilayer switching, is the shortest or longest match used as the layer-3 destination?

A

The LONGEST match is always considered the best match.

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21
Q

What determines where a packet is forwarded?

A

Destination IPv4 Address. The routing table is used for the routing decision.

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22
Q

What happens at every hop that an IP packet hits?

A

L2 frame header is de-capsulated to remove L2 header. It updates source MAC (outbound interface) and destination MAC address (Next hop) then encapsulates the L2 header for transmission

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23
Q

When would a L3 header be changed

A

When it is used in PAT or NAT.

24
Q

Name the slowest type of switching?

A

Process Switching. Because the CPU processes every frame.

25
Q

What is Fast Switching?

A

Fast switching uses CPU to lookup the first frame and put it into a cache. It uses the cache to forward the rest of the frames in the data stream. This is faster than process switching but slower than CEF.

26
Q

What is CEF?

A

Cisco Express Forwarding is the fastest switching method. Forwarding table created in hardware beforehand. All packets will be switched using hardware. Multilayer switches and routers use CEF.

27
Q

Explain the L2 Switching Process.

A
  1. The switch will verify the checksum on the Ethernet frame to amke sure it’s not corrupted.
  2. The switch receives an ethernet frame and adds the source MAC address to the MAC address table.
  3. The switch forwards the ethernet frame to the correct interface if it knows the destination MAC address, if not it will flood the frame.

There is NO ALTERATION of the ethernet frame.

28
Q

Explain receiving a IP Packet on a multilayer switch.

A
  1. Verify checksum on Frame
  2. Verify checksum on Packet
  3. Check routing table
  4. Check ARP table for L2 to L3 Mapping to H2.
  5. Change destination MAC from FFF to BBB
  6. Change source MAC from AAA to GGG
  7. Decrease TTL by one, recalculate checksum
  8. The ethernet frame carrying the IP packet will be sent out of the interfce toward H2.
32
Q

What is the recursive lookup process (example: 10.10.10.5)

A

Preform recursive lookup

  1. 10.10.5 via 11.11.11.1
  2. 11.11.1 via 12.12.12.1
  3. 12.12.1 directly connected, FastEthernet 0/0
33
Q

What are the 3 main steps in moving traffic.

A
  1. Routing-Longest matching of destination address
    1. Recursive Lookups until you find the outbound interface
  2. Switching
    1. Moving packets between interfaces
  3. Encapsulation
    1. Build new layer 2 deader based on outgoing media
    2. two types of interfaces, P2P or Multipoint
34
Q

What is microsegmentation?

A

One host, one collision domain.

35
Q

What are the three actions that a switch can do with a frame?

A

Forward, filter or flood.

36
Q

How is a MAC address table built?

A

With the source MAC addresses of incoming frames.

37
Q

When will a switch flood a frame?

A

When the destination MAC address of a frame is not in the switch’s MAC address table. Unkown unicast frames are always flooded. Broadcast frames are always flooded. Multicast frames are always flooded.

38
Q

When will a switch forward a frame?

A

When the destination MAC address of a frame is in the switch’s MAC address table.

39
Q

When will a switch filter a frame?

A

When the destination MAC address is located on the port that received the frame.

40
Q

What is the default aging time of the MAC address table?

A

5 minutes.

41
Q

What is ARP throttling, or throttling adjacency mean?

A

That until an APR reply is received, additional ARP requests will dropped so they don’t fill up the input queues.

42
Q

Within a frame, what does an Ethernet switch use to make decisions about forward frames?

A

The destination MAC address.

43
Q

What is the difference between routing and Layer 3 switching?

A

In one sense, nothing. In another sense, the term routing implies that the forwarding is software-based where the term Layer 3 switching implies that hardware-based forwarding is used. In both cases, general-purpose CPUs are used to handle control plane functions (such as routing protocols and configuration).

44
Q

Can the router-on-a-stick approach to inter-VLAN routing also support inter-VLAN bridging?

A

Yes. Simply configure a bridge-group on multiple subinterfaces.

45
Q

Does MLS eliminate the need for a router?

A

No. Because MLS is a routing switch Layer 3 switching technique, it relies on caching information learned from the actions of a real router. The router must therefore be present to handle the first packet of every flow and perform the actual access list processing.

46
Q

Does MLS require a router that runs the router-based NetFlow mechanism?

A

No. Other than the fact that MLS and NetFlow on the routers can both be used for detailed data collection, the two mechanisms are completely separate. A router doing MLS processing does not need to be running router NetFlow.

47
Q

In MLS, does the router create the shortcut entry and download it to the Layer 3 CAM table located in the Catalyst’s NFFC or MSFC/PFC?

A

No. Many people are of the opinion that MLS is simply a router running router NetFlow that learns a flow and then ships the results of this flow to a Catalyst. This is not the case. First, if it were the case, the flow would probably be over before the information could be learned by the Catalyst. Second, the NFFC learns the cache information totally by itself. It only needs to know the MAC address and VLAN information of the router (it learns this via MLSP).

48
Q

What effect does the mac address-table aging-time 180 command have on the MAC address-table?

A

This is how long a dynamic MAC address will remain in the CAM table.

49
Q

In a Cisco switch, what is the default period of time after which a MAC address ages out and is discarded?

A

300 seconds

50
Q

If a network engineer applies the command mac-address-table notification mac-move on a Cisco switch port, when is a syslog message generated?

A

A MAC address or host moves between different switch ports.

51
Q

What is unknown unicast flooding

A

MAC addresses are learned from the source MAC of incoming frames. If the destination address is unknown, the frame is flooded out all except the receiving port.

52
Q

what do multilayer switches do?

A

both layer 2 switching and IVR (inter-vlan routing)

53
Q

where does L2 switching occur?

A

between interfaces that are assigned to L2 VLANs or L2 trunks

54
Q

Where does layer 3 switching occur?

A

between any type of interface as long as the interface can have an L3 address assigned

55
Q

What is the traditional MLS view of switching?

A

route once, switch many

56
Q

Study the exhibit carefully. Both host stations are part of the same subnet but are in different VLANs. On the basis of the information presented in the exhibit, which statement is true about an attempt to ping from host to host? samesubnetDifferentVLAN A – Layer 3 device is needed for the ping command to be successful. B – A trunk port will need to be configured on the link between SA and SB for the ping command to be successful. C – The two different hosts will need to be in the same VLAN in order for the ping command to be successful. D – The ping command will be successful without any further configuration changes.

A

Answer: D Explanation: For two hosts in different VLANs, we must use a layer 3 device to transport packages between them. However, in this case both switches are set in “access” mode therefore the VLAN information sent between them will be set as untagged. Moreover, they are in the same subnet so they can ping each other without a layer 3 device.

57
Q

Based on the following exhibit, which problem is preventing users on VLAN 100 from pinging addresses on VLAN 200?

routing_interVLAN

A – Native VLAN mismatch.
B – Subinterfaces should be created on Fa0/7 and Fa0/8 on DLS1.
C – Trunking needs to be enabled.
D – The ip routing command is missing on DLS1.

A

Answer: D

Explanation:

To allow communication between two VLANs, we need to enables Layer 3 routing on the switch with the “ip routing” command. Some flatforms are enabled by default but some are not.

58
Q

Based on the network diagram and routing table output in the exhibit, which one of these statements is true?

vlan10_20_routing

A – InterVLAN routing has been configured properly, and the workstations have connectivity to each other.
B – InterVLAN routing will not occur since no routing protocol has been configured.
C – Although interVLAN routing is not enabled, both workstations will have connectivity to each other.
D – Although interVLAN routing is enabled, the workstations will not have connectivity to each other.
E – None of the above.

A

Answer: A

Explanation:

In the output we can see both VLAN10 and VLAN20 are shown up (as networks 10.1.1.0 and 10.2.2.0) so the routing has been configured properly. Notice that the “C” letter indicates that these networks are directly connected with the router.

myCCNP Switch 300-115 (73 decks)

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