Re: IERS Lab4 Task1.3 - Loopguard and UDLD

Actually two different technologies that CAN be used to solve the
exact same problem -- spanning-tree loops due to unidirectional links.
 I think the confusion here is that this is not the ONLY thing UDLD
does. This particular problem just so happens to be one particular
thing UDLD can help fix by nature of what it is to begin with.

On Sun, Jan 24, 2010 at 2:32 PM, Joe Astorino <jastorino_at_ipexpert.com> wrote:
> Marko,
>
> I do agree that everything here is absolutely correct. I'm simply
> saying that UDLD and loop guard are both technologies that can prevent
> against spanning-tree loops due to unidirectional links. They
> accomplish that in different ways. UDLD does it by detecting the link
> as being unidirectional in the first place and taking action.
> Loopguard does it by taking a different action in spanning-tree (When
> the non-designated port stops receiving BPDUs it goes into inconsitent
> state instead of starting to forward because it assumes it is the new
> DP)
>
> So yes -- two different technologies but two technologies that can be
> used to solve a similar problem.
>
> On Sun, Jan 24, 2010 at 12:56 PM, Marko Milivojevic <markom_at_ipexpert.com> wrote:
>> While I hate to disagree with Joe (I usually end up losing those
>> arguments), I have to in this case... at least in one part.
>>
>> UDLD and Loop Guard *do not* solve the same problem. They are designed
>> to solve entirely different issues at different layers, though their
>> functionality overlaps in one single scenario.
>>
>> UDLD is, essentially, L1.5 protocol. It will detect unidirectional
>> links (using its own mechanism) and disable the port if it receives no
>> responses from its UDLD partner on the other side. In a case when
>> there is bidirectional link, you can still have L2 loop...
>>
>> So, what exactly is the L2 loop, then? Imagine having an access
>> network of two access switches, where each is connected to the root
>> switch with one uplink. Access ports are configured with portfast, to
>> make client workstations connect faster. What happens when someone
>> smart comes there and decides to "have 200 megs to his workstation",
>> by connecting two ports to a hub? All links are bidirectional, there
>> are no failures... only one nice STP loop... and mess in your entire
>> network. Now, this is the problem Loop Guard is designed to solve.
>> Granted, it can help with unidirectional links, but... Unidirectional
>> links have another problem...
>>
>> Let's say that we have a link that is unidirectional only ...
>> sometimes. In other words, it's flapping, but only in one direction
>> (long fiber links can do this if optical receiver is burned through,
>> for example). UDLD may or may not detect this, so using Loop Guard as
>> an additional precaution is perfectly legitimate approach.
>>
>> --
>> Marko Milivojevic - CCIE #18427
>> Senior Technical Instructor - IPexpert
>>
>> Mailto: markom_at_ipexpert.com
>> Telephone: +1.810.326.1444
>> Fax: +1.810.454.0130
>> Community: http://www.ipexpert.com/communities
>>
>> On Sun, Jan 24, 2010 at 17:16, Nadeem Rafi <nrafia_at_gmail.com> wrote:
>>> Thanks for this link.. mis-wiring is new to me :) so much to learn in this
>>> short period of life.
>>>
>>> Thanks again.
>>>
>>> On Sun, Jan 24, 2010 at 8:08 PM, Joe Astorino <jastorino_at_ipexpert.com>wrote:
>>>
>>>> Hello,
>>>>
>>>> UDLD and loopguard are essentially two ways to solve the same problem
>>>> using different methods. Like Nadeem said, UDLD physically detects
>>>> the uni-directional links, whereas loopguard is more geared towards
>>>> STP specifically. Typically you will deploy one or the other. You
>>>> may want to check out the following link which does a nice comparison
>>>> : )
>>>>
>>>>
>>>> http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094640.shtml#loop_guard_vs_uld
>>>>
>>>> On Sun, Jan 24, 2010 at 7:05 AM, Michael McFarlin
>>>> <router.genie_at_gmail.com> wrote:
>>>> > Experts,
>>>> >
>>>> > I have a question about UDLD and Loopguard in one of the IERS labs. I
>>>> don't
>>>> > think that loopguard is needed at all here. Why would you have to worry
>>>> > about SW1 making the Fa0/15 a designated port if UDLD has already taken
>>>> the
>>>> > port down? By default UDLD acts faster than Loopguard by default right?
>>>> >
>>>> >
>>>> > Task
>>>> >
>>>> > Administrators of your network are concerned about SW1 and SW2 not
>>>> > being able to detect a link failure on port Fa0/15.
>>>> >
>>>> > Configure SW1 and SW2 so that port Fa0/15 is brought down in the case
>>>> > that either switch can send traffic, but not receive, or vice versa.
>>>> >
>>>> > As an additional precaution, configure SW1 so that interface Fa0/15 is
>>>> not
>>>> > mistakenly elected as a designated port in the above case.
>>>> >
>>>> > Answer
>>>> >
>>>> > SW1:
>>>> > interface FastEthernet0/15
>>>> > udld port aggressive
>>>> > spanning-tree guard loop
>>>> > SW2:
>>>> > interface FastEthernet0/15
>>>> > udld port aggressive
>>>> >
>>>> >
>>>> > -Mike
>>>> >
>>>> >
>>>> > Blogs and organic groups at http://www.ccie.net
>>>> >
>>>> > _______________________________________________________________________
>>>> > Subscription information may be found at:
>>>> > http://www.groupstudy.com/list/CCIELab.html
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>> Regards,
>>>>
>>>> Joe Astorino CCIE #24347 (R&S)
>>>> Sr. Technical Instructor - IPexpert
>>>> Mailto: jastorino_at_ipexpert.com
>>>> Telephone: +1.810.326.1444
>>>> Live Assistance, Please visit: www.ipexpert.com/chat
>>>> eFax: +1.810.454.0130
>>>>
>>>> IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA
>>>> (R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice,
>>>> Security & Service Provider) Certification Training with locations
>>>> throughout the United States, Europe and Australia. Be sure to check
>>>> out our online communities at www.ipexpert.com/communities and our
>>>> public website at www.ipexpert.com
>>>>
>>>>
>>>> Blogs and organic groups at http://www.ccie.net
>>>>
>>>> _______________________________________________________________________
>>>> Subscription information may be found at:
>>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>
>
>
> --
> Regards,
>
> Joe Astorino CCIE #24347 (R&S)
> Sr. Technical Instructor - IPexpert
> Mailto: jastorino_at_ipexpert.com
> Telephone: +1.810.326.1444
> Live Assistance, Please visit: www.ipexpert.com/chat
> eFax: +1.810.454.0130
>
> IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA
> (R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice,
> Security & Service Provider) Certification Training with locations
> throughout the United States, Europe and Australia. Be sure to check
> out our online communities at www.ipexpert.com/communities and our
> public website at www.ipexpert.com
>

-- 
Regards,
Joe Astorino CCIE #24347 (R&S)
Sr. Technical Instructor - IPexpert
Mailto: jastorino_at_ipexpert.com
Telephone: +1.810.326.1444
Live Assistance, Please visit: www.ipexpert.com/chat
eFax: +1.810.454.0130
IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA
(R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice,
Security & Service Provider) Certification Training with locations
throughout the United States, Europe and Australia. Be sure to check
out our online communities at www.ipexpert.com/communities and our
public website at www.ipexpert.com
Blogs and organic groups at http://www.ccie.net