| Author |
CCNA Questions ???
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| lkyoong 2001-04-20, 9:33 am |
| Got some questions here that i need some clarification or answers too.
1.Which of the following statements about frame tagging are true? Choose all that apply.
a)A unique identifier is placed in the header of each segment.
b)Frame tagging assigns an unique identifier to each frame.
c)Frame tagging remains constant regardless of frame size.
d)The destination switch discards the identifier upon receipt of the packet.
My answer would be b and d.
2. How to check that STP is working (VLAN1) properly in a switched network when the "show spantree" command is used?
a)Bridge identifier has priorty 32768
b)Address is 0080F087EC01
c)Designated port has priority 0
d)VLAN1 is executing the IEEE spanning tree protocol.
My answer would be d but i am not sure.
3.Which line from the output of "show spantree 1" indicates that VLAN1 is functioning properly.
a)Root mode is Fast Ethernet 0/26
b)Port Ethernet 0/1 of VLAN1 is forwarding.
c)Designated port in Ethernet 0/1 path cost 10.
d)Designated root has priority 0, address 0000.766EB423
e)VLAN1 is executing the ISL compatible spanning tree protocol.
I don't know the answer to this but it seems to be similar to question 2.
Hope some one can help me here. TIA  | |
| JerryL 2001-04-20, 11:03 am |
| Hi;
The answers are:
1. a and b
2. I'm not 100% sure, but I would agree with you that the answer is d
3. b
JerryL | |
| dmaftei 2001-04-20, 11:13 am |
| quote:
Originally posted by JerryL
3. b
What if port Ethernet0/1 is part of VLAN 2?
Food for thought.  | |
| JerryL 2001-04-20, 11:20 am |
| Hey Dmaftei;
Good question, but it doesn't work in this case. The command is "show spantree 1" which is referring to VLAN 1, not 2. and the response is also referring to VLAN1.
JerryL | |
| lkyoong 2001-04-20, 12:12 pm |
| Thanks for the responses.
BTW i always thought that frame tagging was putting a header onto the frame.
But on a segment? Is this correct? | |
| dmaftei 2001-04-20, 1:01 pm |
| quote:
Originally posted by JerryL
The command is "show spantree 1" which is referring to VLAN 1, not 2.
That's precisely the point. Suppose your switch is configured as follows:
VLAN1: ports 5 through 24
VLAN2: ports 1, 2, 3 and 4
("port 1" is "Ethernet 0/1", etc.)
VLAN1 works perfectly fine. You do a "show spantree 1". Are you going to see a line "Port Ethernet 0/1 of VLAN1 is forwarding."? Nope, because Ethernet 0/1 does not belong to VLAN1. You'll see something like this:
VLAN1 is executing the IEEE compatible Spanning Tree Protocol
Bridge Identifier has priority 32768, address 0003.6B33.8380
Configured hello time 2, max age 20, forward delay 15
Current root has priority 32768, address 0003.6B33.8380
Root port is N/A, cost of root path is 0
Topology change flag not set, detected flag not set
Topology changes 0, last topology change occured 0d00h00m00s ago
Times: hold 1, topology change 8960
hello 2, max age 20, forward delay 15
Timers: hello 2, topology change 35, notification 2
Port Ethernet 0/5 of VLAN1 is Forwarding
...
Port Ethernet 0/6 of VLAN1 is Forwarding
...
etc
So, you'll never see a line "Port Ethernet 0/1 ..." in the output of "show spantree 1". See my point?
Cheers! | |
|
| quote:
Originally posted by lkyoong
1.Which of the following statements about frame tagging are true? Choose all that apply.
a)A unique identifier is placed in the header of each segment.
b)Frame tagging assigns an unique identifier to each frame.
c)Frame tagging remains constant regardless of frame size.
d)The destination switch discards the identifier upon receipt of the packet.
My answer would be b and d.
The term frame tagging is used about the way 802.1Q labels frames with its VLAN membership when transporting over a trunk link. The term encapsulation is used to describe the similar process in ISL.
Frame tagging will add 4 bytes to the header. Among those is the VLAN ID. The VLAN ID is the same for all frames belonging to the same VLAN. The rest of the 4 bytes can be considered constant for now.
This makes C and D obvious answers. To accept A or B as answers would stretch the meaning of unique.
Terje | |
| JerryL 2001-04-20, 5:09 pm |
| 
Here's an interesting turn of events:
I have Exam Essentials 5.5 and this question is on the test prep. The answer that they provide is as follows:
A unique identifier is placed in the header of each segment; and
Frame tagging assigns a unique identifier to each frame.
In their reasoning they give the following:
Frame tagging uniquely assigns a user-defined ID in each frame to the header. Once the switch has examined the ID, it discards the identifier before the packet is transmitted to the destination.
They provide references to the following:
www.cisco.com/warp/public/cc/pd/ios...dlit/627_pp.htm and
page 306 and 307 of the Sybex book.
Here is what Todd Lammle says:
Frame identification (frame tagging) uniquely assigns a user-defined ID to each frame. This is sometimes referred to as a VLAN ID or color.
He goes on to mention:
Once the frame reaches an exit to an access link, the switch removes the VLAN identifier. The end device will receive the frames without having to understand the VLAN identification.
Basically, EE is saying a and b are correct, but in thier own explanation, they give the answer as b and d. Therefore, I would admit that Terje is correct by his statement. The confusing part is that EE contridicts itself with its own references and explantation. Ever wonder how many other answers are wrong?
Just goes to prove that you can't trust the test preps all the way either.
JerryL | |
| lkyoong 2001-04-20, 7:24 pm |
| JerryL
The latest EE 5.5 update has changed the answer of that question to
1.Frame tagging assigns a unique identifier to each frame.
2.The destination switch discards the identifier upon receipt of the packet.
I noticed that EE 5.5 does have a few mistakes and this was one of the questions they corrected but wasn't sure so i seeked clarification. At least i know now (thanks to Terje) which answers and why they are correct.
However the question on the CDP Timer 90 and a question on which access list is correct has not been corrected. No idea how they could have missed that one.
Once thanks to all for the replies. | |
| lkyoong 2001-04-20, 7:38 pm |
| Terje
After reading your post, i am wondering about the word unique.
Don't the VLAN IDs need to be unique or how will the switch or router know which VLAN the packet belongs to?
The VLAN ID size will be constant for sure but there should be some difference in the VLAN ID.
Also to dmaftei, your answer has merit too, since if VLAN1 has only ports 5 - 24 configured. Would that make the answer : VLAN1 is executing the ISL compatible spanning tree protocol.
Thanks again | |
| dmaftei 2001-04-20, 7:56 pm |
| quote:
Originally posted by Terje
...would stretch the meaning of unique.
I believe unique means unique with respect to the switching fabric. However, this makes the question very poorly worded.
quote:
Originally posted by lkyoong
...to dmaftei, your answer has merit too...
Thank you for the credit... | |
|
| quote:
Originally posted by lkyoong
Terje
After reading your post, i am wondering about the word unique.
Don't the VLAN IDs need to be unique or how will the switch or router know which VLAN the packet belongs to?
The ID in the tag will be unique to the VLAN but not to the FRAME. Multiple frames will have the same ID if they belong to the same VLAN. The ID will be different if they belong to different VLANs.
The size of the frame will not influence how it is tagged. All frames on the same VLAN will be tagged identically (disregarding for the moment the 3 bit priority field and a bit that differs between token-ring and Ethernet).
Terje |
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