Cisco QOS question 642-642 1

[CiscoKidUK]

Hi Guys,

I am currently looking at resit my QOS as i failed last week! i have been looking at a question i got on the exam i want to check i know the question for next time. the goes like. Refer to the exhibit. A typical config involving a IP phone and PC, according to QOS best pratices where does the Trust boundary normally exist?

The Exhibit looks like a core switch, a distribution switch, a access switch, a IP Phone and a PC. The answers are marked between each item ie between the pc and IP phone or between the IP Phone and the Access switch etc.

could some please advise

Thanks

Matt

 

[maczen]

I am merely guessing here but you place the phone in a separate VLAN than the PC for both QoS and security reasons.. Programs like VOMIT... So I would guess between the PC and the phone since that would be the lowest layer. Will have to wait on the Pros though!

B Haines
CCNA R&S, ETA FOI

 

[Cluebird]

In this case the trust boundary would be at the access layer switch. You would configure the switch to trust the IP phone traffic but not the PC traffic. The link between the IP phone and switch would be where the boundary would be established. If the access layer switch can't support QoS to establish the trust boundary, you can push the boundary to the distribution layer switches. In that case, the trust boundary would be the link between the access and distribution switch. However, you should never have the trust boundary in the core.

HTH

 

[lerdalt]

My rule of thumb when I sat for the QoS exam was the trust boundary is where I can trust the DSCP markings from a device.

 

[maczen]

Thanks guys.. That is why I said wait for the Pros.. LoL

B Haines
CCNA R&S, ETA FOI

 

[Belushi]

I know everyone in here took a crack at answering your question but the problem is that the answer will depend mainly on what was provided in that "Typical config" you are not showing here. More than likely the best practice for that trust boundary is between the phone and the PC. That is not a given though based upon the information given. By defauly the trust boundary is between the switchport and the phone. Cisco tests you on this specifically to make sure you udnerstand what the commands are doing.

 

[lerdalt]

Good point Belushi. Cisco also tests you assuming it is a Cisco phone and is marking the packets for you as it thinks it should.

I remember the trust boundary was confusing at first. Took me a few times reading the section to get it down. Of course now that was almost a year ago, so it has since been replaced with BGP/MPLS information, until I start working with IP phones again.

 

[Belushi]

Just keep at your studying and you should be fine. I personally found Wendell Odom's Cisco Press book for the subject to be more than enough for me. I had a ton of experience though with the subject before ever taking the test. I actually found it to be the easiest of the 9 Cisco tests I have taken thus far. Finished in 45 minutes and got a 960 or something. BGP on the other hand, that was tough.

 

[DallasBPF]

I found the CBT nuggets video a very good resouce, you get to watch Jeremy go into a router and configure it and show what happens for differen things...

------------------------------------
Dallas, Texas
Telecommunications Tech
CCVP, CCNA, Net+

CCNP in the works

 

[lerdalt]

I agree with Belushi, I think Odom's book is the standard when it comes to QoS.