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- CCNP Switching 642-813
21.
You need to connect two Company core switches via an ISL trunk. Which statement is true
regarding the configuration of ISL trunks?
- A.A Catalyst switch cannot have ISL and IEEE 802.1q trunks enabled.
- B.All Catalyst switches support ISL trunking.
- C.A Catalyst switch will report giants if one side is configured for ISL while the other side is not.
- D.ISL trunking requires that native VLANs match.
- E.None of the other alternatives apply
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
| The Inter-Switch Link (ISL) protocol is a Cisco proprietary method for preserving the source VLAN identification of frames passing over a trunk link. ISL performs frame identification in Layer 2 by encapsulating each frame between a header and trailer. Any Cisco switch or router device configured for ISL can process and understand the ISL VLAN information. ISL is primarily used for Ethernet media, although Cisco has included provisions to carry Token Ring, FDDI, and ATM frames over Ethernet ISL. (A Frame-Type field in the ISL header indicates the source frame type.) When a frame is destined out a trunk link to another switch or router, ISL adds a 26-byte header and a 4-byte trailer to the frame. The source VLAN is identified with a 10-bit VLAN ID field in the header. The trailer contains a cyclic redundancy check (CRC) value to ensure the data integrity of the new encapsulated frame. Figure 6-3 shows how Ethernet frames are encapsulated and forwarded out a trunk link. Because tagging information is added at the beginning and end of each frame, ISL is sometimes referred to as double tagging . |
22.
Which of the following technologies would an Internet Service Provider use to support overlapping
customer VLAN ID's over transparent LAN services?
- A.802.1q tunneling
- B.ATM
- C.SDH
- D.IP Over Optical Networking
- E.ISL
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
|
Understanding How 802.1Q Tunneling Works : The 802.1Q tunneling feature supports secure virtual private networks (VPNs). 802.1Q tunneling enables service providers to keep traffic from different customers segregated in the service provider infrastructure while significantly reducing the number of VLANs required to support the VPNs. 802.1Q tunneling allows multiple customer VLANs to be carried by a single VLAN on the Catalyst 6000 family switch without losing their unique VLAN IDs. When you configure 802.1Q tunneling on the Catalyst 6000 family switch, traffic to be tunneled comes into the switch from an 802.1Q trunk port on a neighboring device and enters the switch through a port configured to support 802.1Q tunneling (a tunnel port). When the tunnel port receives traffic from an 802.1Q trunk port, it does not strip the 802.1Q tags from the frame header but, instead, leaves the 802.1Q tags intact and puts all the received 802.1Q traffic into the VLAN assigned to the tunnel port. The VLAN assigned to the tunnel port then carries the tunneled customer traffic to the other neighboring devices participating in the tunnel port VLAN. When the tunneled traffic is received by an 802.1Q trunk port on a neighboring device, the 802.1Q tag is stripped and the traffic is removed from the tunnel. |
23.
If you were to configure an ISL Ethernet trunk between two Cisco switches, named R1 and R2,
what would you have to include at the end of the link for the trunk to operate correctly? (Select
two)
- A.An identical VTP mode
- B.An identical speed/duplex
- C.An identical trunk negotiation parameter
- D.An identical trunk encapsulation parameter
- Answer & Explanation
- Report
Answer : [B, D]
Explanation :
Explanation :
| In order for a trunk to be operational, the speed and duplex settings must match at each end of the trunk, and both switches must use the same trunking encapsulation (802.1Q or ISL). |
24.
If you were to set up a VLAN trunk over a Fast Ethernet link on switch R1, which trunk mode
would you set the local port to on R1 if you wanted it to respond to requests from its link partner
(R2) and become a trunk?
- A.Auto
- B.Negotiate
- C.Designate
- D.No negotiate
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
| Only ports in desirable and auto mode will negotiate a channel (either desirable-auto or desirabledesirable). Ports in on mode will only form a functional channel with other ports in on mode (they will not negotiate a channel with ports in desirable or auto mode). |
25.
Which of the following trunking modes are unable to request their ports to convert their links into
trunk links? (Select all that apply)
- A.Negotiate
- B.Designate
- C.No negotiate
- D.Auto
- E.Manual
- F.Off
- Answer & Explanation
- Report
Answer : [C, D]
Explanation :
Explanation :
| Auto is a trunking mode but does not actively negotiate a trunk. It requires opposite side to be trunk or desirable, and will only respond to requests from the other trunk link. No-negotiate will configure the link to be unable to dynamically become a trunk; since no requests will be sent it will not respond to requests from other trunk links from a different switch. |
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