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VLAN Questions 2

November 24th, 2018 in SWITCH 300-115 Go to comments

Question 1

Explanation

First let’s review main characteristics of three layers in a campus network:

* Access layer:

+ Low cost per switch port
+ High port density
+ Scalable uplinks to higher layers
+ User access functions such as VLAN membership, traffic and protocol filtering, and quality of service (QoS)
+ Resiliency through multiple uplinks

* Distribution Layer:

+ Aggregation of multiple access-layer devices
+ High Layer 3 throughput for packet handling
+ Security and policy-based connectivity functions through access lists or packet filters
+ QoS features
+ Scalable and resilient high-speed links to the core and access layers

* Core layer:

+ Very high throughput at Layer 3
+ No costly or unnecessary packet manipulations (access lists, packet filtering)
+ Redundancy and resilience for high availability
+ Advanced QoS functions

We can see at Distribution and Core layers, Layer 3 throughput (routing) is very high -> B is correct.

Nowadays, end-to-end VLANs are not recommended in an enterprise network, unless there is a good reason. In an end-to-end VLAN, broadcast traffic is carried over from one end of the network to the other, creating the possibility for a broadcast storm or Layer 2 bridging
loop to spread across the whole extent of a VLAN. This can exhaust the bandwidth of distribution and core-layer links, as well as switch CPU resources. Now the storm or loop has disrupted users on the end-to-end VLAN, in addition to users on other VLANs that might
be crossing the core.

When such a problem occurs, troubleshooting becomes more difficult. In other words, the risks of end-to-end VLANs outweigh the convenience and benefits.

From that we can infer VLAN traffic should be local to the switch -> D is correct.

(Reference: CCNP SWITCH 642-813 Official Certification Guide)

Question 2

Explanation

Normal access port belongs to VLAN 1 by default but this question asks about dynamic-access port. This is a quote from Cisco website about dynamic-access port:

Dynamic-Access Port VLAN Membership

“A dynamic-access port can belong to only one VLAN with an ID from 1 to 4094. When the link comes up, the switch does not forward traffic to or from this port until the VMPS provides the VLAN assignment. The VMPS receives the source MAC address from the first packet of a new host connected to the dynamic-access port and attempts to match the MAC address to a VLAN in the VMPS database.

If there is a match, the VMPS sends the VLAN number for that port. If the client switch was not previously configured, it uses the domain name from the first VTP packet it receives on its trunk port from the VMPS. If the client switch was previously configured, it includes its domain name in the query packet to the VMPS to obtain its VLAN number. The VMPS verifies that the domain name in the packet matches its own domain name before accepting the request and responds to the client with the assigned VLAN number for the client. If there is no match, the VMPS either denies the request or shuts down the port (depending on the VMPS secure mode setting).”

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_55_se/configuration/guide/scg_2960/swvlan.html

So answer B is the best choice here.

Note: “Dynamic-Access port” is a different from the DTP “Dynamic Auto” mode. We can configure “Dynamic-Access port” with the command “switchport access vlan dynamic” (not “switchport mode dynamic auto”).

Question 3

Question 4

Question 5

Explanation

Normal range VLANs are from 1 to 1005. Extended range VLANs are from 1006 to 4094.

In VTP version 1 and 2, extended-range VLANs are not saved in the VLAN database; they are saved in the switch running configuration file. You can save the extended-range VLAN configuration in the switch startup configuration file by using the copy running-config startup-config privileged EXEC command. VTP version 3 saves extended-range VLANs in the VLAN database.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/configuration/guide/scg3750/swvlan.html

Therefore answer B is correct, except that the extended range VLANs should be from 1006-4094 (not 4096).

Question 6

Explanation

When the native VLAN is tagged, all VLANs will be tagged.

Question 7

Explanation

When the switch is in VTP server or transparent mode, you can configure VLANs in the VLAN database mode. When you configure VLANs in VLAN database mode, the VLAN configuration is saved in the vlan.dat file, not the running-config or startup-config files. To display the VLAN configuration, enter the show running-config vlan command.

User-configurable VLANs have unique IDs from 1 to 4094. Database mode supports configuration of IDs from 1 to 1001, but not the extended addresses from 1006 to 4094.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25ew/configuration/guide/conf/vlans.html#wp1037080

Question 8

Explanation

Normal range VLANs are from 1 to 1005 (in which VLANs 1002 to 1005 are Cisco defaults for FDDI and Token Ring. You cannot delete these VLANs). Extended range VLANs are from 1006 to 4094.

Question 9

Question 10

Comments
  1. KOLE
    September 11th, 2019

    first set of questions i came across that has no comments…Let me be the first to say something
    HELLO :)

  2. VTP-is-garbage
    September 14th, 2019

    HELLO!

  3. Grinder
    September 17th, 2019

    Hi! Has anyone recently given the 300-115 exam by training from this site?
    I used Digitaltut + OCG with success for route exam, I hope it will be the same for this one.

  4. Efiko
    September 21st, 2019

    So the explanation of Q5 reads “VTP version 3 saves extended-range VLANs in the VLAN database.” So how was “B” confidently chosen over “D”?

  5. tom
    September 23rd, 2019

    Question 6
    Question about the behavior of VLAN 1 BPDUs in a situation where the native VLAN configured as VLAN 99 and the native VLAN is tagged. (Choose two)
    A. Normal STP VLAN 1 BPDU travel across VLAN 99 untagged
    B. PVST+ VLAN 1 BPDU travel across VLAN 99 tagged
    C. Normal STP VLAN 1 BPDU travel across VLAN 1 untagged
    D. PVST+ VLAN 99 BPDU travel across VLAN 99 tagged

    Answer: B D

    B looking not correct. in pvst+ bpdu vlan 1 can’t go across vlan 99.
    i’m for C and D
    here some tests, looking like standard stp bpdu always use vlan 1 and untagged
    https://community.cisco.com/t5/switching/how-bpdu-is-transmitted-with-native-vlan-for-pvst-and-mstp/td-p/1631995

  6. xela
    October 8th, 2019

    Question 6 !
    tom , i think A and D but i dont sure.

  7. tom
    October 15th, 2019

    Q6
    looks like somthing miss in that questin
    maybe answer A must be “Normal STP VLAN 1 BPDU travel across VLAN 99 TAGGED”
    then all will be fine
    with current options only D looking correct

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