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
