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Q in Q

Ok this is great. spent ages wondering how I could do this, even went as far as working out work around to achive this idea...

then read the documentation and found out some one got there first!!

anyway this is just what i needed. For reasons best left to BT, i ended up having to put my 1841 the oposite side of site to the rest of the network it routers for.

with two choises to get the two connected. Run about 1km of fibre (a little of an over kill for a network of 10 end devices and a cheap ADSL link), or creating all the vlans on our main corprae network and trunking it across that.

All i could think of was  why can't I trunk it all in one vlan to have as little effact on the corprate network as possible... So after  fiddeling around a bit, I bit the bullet and opened the configuration PDF..  It seems cisco have already thought of this and wow what simple config. 5 min later all up and running and working fine... a singel VLAN created on the corprate network. a single port either side configured as a tunnel and in effact I have turned my corprate network in to a very expensive and long eithernet cable between my 1841 and the switch it needs to connect to. (router on a stick setup)

well fine untill I try to FTP across it... errrr whats all that about, it just stops.... Go back to read a bit more about it oh it seems I skiped the MTU bit.. have another look and theres the problem... that extra 4byte of valn tag is stopping it working!!

DAMM!! so what I need to change the whole corprate network to support jumbo frames!! reboot every switch to update it!! (you have to reboot a cisco swith to update the MTU size!!) some how cant see manger agreeing with that...

Ok next idea I can change the MTU on the router interface

#int f0/0

#mtu 1490

Wow that did it, now the FTP works fine. But still some packets seem to be getting lost along the way, and 90% of webpages will not display? whats that all about??

I need a bit of help on the MTU side of things. how can i insure that my network will run using a smaller MTU size. the 1841 is running with a adsl wic installed (so running the ADSL link, a zone based firewall, multi vlan routing, NAT, and IPS). it seems to some times throuh up errors about fragmented frames and stuff. I knwo its a lot for one router to run but the network is very low usage (a few very lightly uterlised webservers < 500meg a month total, and a few PC's used sporadicaly to browse the internet) Its realy jsut proof of consept.

what i want is the ethernet side to run using a MTU of 1490 (so it can be doubble tag with out affecting the 1514 limit of ethernet), Do i need to do any more than change the MTU size on the ethernet interface that is running the routing. will all devices then use this MTU when they try to reach the DFGW/router?

Thank you


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Last update:
‎11-16-2009 02:34 PM
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