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
