The only thing is the time that concerns me. -- Marko Milivojevic - CCIE #18427 (SP R&S) Senior CCIE Instructor - IPexpert
:: This message was sent from a mobile device. I apologize for errors and brevity. :: On Oct 18, 2012, at 10:58, Bob McCouch <[email protected]> wrote: > I would just do it! But a few minutes ago you said you wouldn't bother > unless the task mentioned a 1500-byte MTU so I was curious why you > lean that way vs the "safe" path. Just concern for the time of a > reboot? > > Bob > -- > Sent from my iPhone, please excuse any typos. > > On Oct 18, 2012, at 11:55 AM, Marko Milivojevic <[email protected]> wrote: > >> It's a tough call to make really. The only correct answer must come >> from someone who's grading the lab. You know what needs to be done to >> be safe, so... why not just do it? >> >> -- >> Marko Milivojevic - CCIE #18427 (SP R&S) >> Senior CCIE Instructor - IPexpert >> >> On Thu, Oct 18, 2012 at 10:46 AM, Bob McCouch <[email protected]> wrote: >>> Ha, got me on that one! Yes, they'd need to specify the df-bit. >>> >>> Here's my question on interpretation then... Cisco's documentation on QQ >>> tunneling states that you "must" bump the MTU: >>> >>> "Because the IEEE 802.1Q tunneling feature increases the frame size by 4 >>> bytes when the metro tag is added, you must configure all switches in the >>> service-provider network to be able to process maximum frames by increasing >>> the switch system MTU size to at least 1504 bytes." (emphasis mine, source >>> http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_46_se/configuration/guide/swtunnel.html#wp1001068) >>> >>> With this in mind, should we not assume that means we have to do it, as the >>> config guide states it as a "must"? Just like MTU on PPPoE interfaces -- >>> I've configured PPPoE dialer interfaces just fine without specifying 1492 >>> MTU, but every time you see an official example config (or an IPExpert DSG >>> solution as well!) they specify the MTU. I have assumed that means I damn >>> well better do it too if I want points on such a task. >>> >>> What do you think, Marko? >>> >>> >>> On Thu, Oct 18, 2012 at 11:38 AM, Marko Milivojevic <[email protected]> >>> wrote: >>>> >>>> On Thu, Oct 18, 2012 at 9:30 AM, Bob McCouch <[email protected]> wrote: >>>>> And if the grading script used "ping X.X.X.X size 1500" to test? :-) >>>> >>>> It would still work, since packets would be fragmented ;-). On the >>>> other hand, if they added "df-bit" to that command... another story. >>>> >>>> That said - unless the lab asks for 1500-byte payload, I wouldn't >>>> bother with it. Then again, if you think rebooting a switch won't take >>>> from your time, why not do it and not worry? Just keep in mind that >>>> changing "system mtu" will change IP MTU as well, which may have >>>> impact for routing protocols running on the switch. Luckily, you can >>>> fix that without a reboot with "system mtu routing" >>>> >>>> -- >>>> Marko Milivojevic - CCIE #18427 (SP R&S) >>>> Senior CCIE Instructor - IPexpert >>>> >>>>> >>>>> How about routing adjacencies? Might OSPF get tripped up by neighbors >>>>> agreeing they have 1500 byte MTU, but not being able to actually pass >>>>> 1500 >>>>> during LSADB sync? >>>>> >>>>> The devil is in those details. >>>>> >>>>> >>>>> On Thu, Oct 18, 2012 at 10:24 AM, Mills, Derek < >>>>> [email protected]> wrote: >>>>> >>>>>> Good questions Bob and I guess I need to know the answers. Perhaps my >>>>>> downfall is that I would configure it, run a few various pings to >>>>>> verify >>>>>> the reachability requirement, and would count those points when there >>>>>> are >>>>>> no other lab requirements indicating that an mtu change is >>>>>> warranted.**** >>>>>> >>>>>> ** ** >>>>>> >>>>>> ** ** >>>>>> >>>>>> ** ** >>>>>> >>>>>> ** ** >>>>>> >>>>>> ** ** >>>>>> >>>>>> *From:* Bob McCouch [mailto:[email protected]] >>>>>> *Sent:* Thursday, October 18, 2012 9:17 AM >>>>>> *To:* Mills, Derek >>>>>> *Cc:* [email protected] >>>>>> *Subject:* Re: [OSL | CCIE_RS] Dot1q Tunnel and MTU**** >>>>>> >>>>>> ** ** >>>>>> >>>>>> Hi Derek,**** >>>>>> >>>>>> ** ** >>>>>> >>>>>> You say "most times" and you are correct. What are the times it >>>>>> wouldn't >>>>>> work? How might those times bite you either while configuring later >>>>>> elements of your lab, or how they might test your solution with a >>>>>> grading >>>>>> script?**** >>>>>> >>>>>> ** ** >>>>>> >>>>>> We must learn the right thing to do, even if IOS doesn't warn you about >>>>>> something. :-)**** >>>>>> >>>>>> ** ** >>>>>> >>>>>> ** ** >>>>>> >>>>>> On Thu, Oct 18, 2012 at 9:01 AM, Mills, Derek < >>>>>> [email protected]> wrote:**** >>>>>> >>>>>> Most times configuring dot1q tunnel in the lab will work just fine >>>>>> without >>>>>> changing the MTU on the switches. What is the opinion on whether we >>>>>> should >>>>>> change it or not? If there is a specific task requirement for it there >>>>>> is >>>>>> no question, but is it expected and standard procedure just to increase >>>>>> it >>>>>> ALL the time when you configure it? Will you miss the points if you >>>>>> don't >>>>>> configure it? >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> DEREK MILLS >>>>>> <>< >>>>>> >>>>>> >>>>>> >>>>>> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- >>>>>> Anheuser-Busch InBev Email Disclaimer www.ab-inbev.com >>>>>> _______________________________________________ >>>>>> For more information regarding industry leading CCIE Lab training, >>>>>> please >>>>>> visit www.ipexpert.com >>>>>> >>>>>> Are you a CCNP or CCIE and looking for a job? Check out >>>>>> www.PlatinumPlacement.com >>>>>> >>>>>> http://onlinestudylist.com/mailman/listinfo/ccie_rs**** >>>>>> >>>>>> ** ** >>>>>> ------------------------------ >>>>>> Anheuser-Busch InBev Email Disclaimer >>>>>> www.ab-inbev.com<http://www.ab-inbev.com/disclaimer.cfm> >>>>> _______________________________________________ >>>>> For more information regarding industry leading CCIE Lab training, >>>>> please visit www.ipexpert.com >>>>> >>>>> Are you a CCNP or CCIE and looking for a job? Check out >>>>> www.PlatinumPlacement.com >>>>> >>>>> http://onlinestudylist.com/mailman/listinfo/ccie_rs >>> >>> _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
