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#209854 - 2015-01-19 06:10 AM Set mtu in Win7
GAW GAW Fresh Scripter Registered: 2010-02-16 Posts: 20 Loc: Tennessee	I can run this script in a command prompt successfully, but not in my kixscript... I am sure it is simple... netsh interface ipv4 set subinterface "local area connection" mtu=1450 store=persistent Thanks for any help! Glenn
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#209856 - 2015-01-19 06:27 AM Re: Set mtu in Win7 [Re: GAW]
GAW GAW Fresh Scripter Registered: 2010-02-16 Posts: 20 Loc: Tennessee	now I see there is a permissions issue, the program doesn't have the credentials to run... G:\>netsh interface ipv4 set subinterface "local area connection 2" mtu=1200 sto re=persistent The requested operation requires elevation (Run as administrator). How can I do that with run or shell?
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#209857 - 2015-01-19 06:45 AM Re: Set mtu in Win7 [Re: GAW]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	the same way as the command prompt. run as admin or disable UAC. _________________________ ! download KiXnet
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#209858 - 2015-01-19 09:17 AM Re: Set mtu in Win7 [Re: Lonkero]
Arend_ Arend_ MM club member Registered: 2005-01-17 Posts: 1896 Loc: Hilversum, The Netherlands	Purely out of interest, why would you set it any lower then 1500 ?
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#209859 - 2015-01-19 04:50 PM Re: Set mtu in Win7 [Re: Arend_]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	the old common reason would be to prevent packet fragmentation over ipsec links. now, windows vista introduced dynamic packet scaling (one of those features causing grief back in the day) and these things should not be needed to change anymore. _________________________ ! download KiXnet
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#209860 - 2015-01-19 05:32 PM Re: Set mtu in Win7 [Re: Lonkero]
Arend_ Arend_ MM club member Registered: 2005-01-17 Posts: 1896 Loc: Hilversum, The Netherlands	Interesting, I never knew about packet fragmentation over IPSec links. I'll investigate that, thanks!
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#209861 - 2015-01-19 08:25 PM Re: Set mtu in Win7 [Re: Arend_]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	nothing much to investigate. if default packet size is 1500, this is what the ipsec endpoint uses, inserts it's headers and rest is for data. I think for ipsec the data was 1460 or 1463 or something like that. now, fragmented packages are be re-combined at the other end. in some special cases though, the delays caused by this or weird software having no-fragment bit on, this will cause connection issues. supposedly even RDP does this: http://www.thincomputing.net/2011/06/28/mtu-size-mismatch-a-major-cause-of-disconnections/ _________________________ ! download KiXnet
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#209862 - 2015-01-19 09:03 PM Re: Set mtu in Win7 [Re: Arend_]
GAW GAW Fresh Scripter Registered: 2010-02-16 Posts: 20 Loc: Tennessee	Something has gone arye in our network. The network engineers still have not figured out what. In trying just to get things back and workable someone tried setting his mtu=1450, he said he ran into a similar problem but it involved a firewall issue and this got them around it. When we tried it it worked! but now I have 200 pc's that need to be changed - and today the other 12 hospitals in our network are seeing the same problem so the potential number of affected pc's is many times more!
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#209863 - 2015-01-19 09:26 PM Re: Set mtu in Win7 [Re: GAW]
NTDOC NTDOC Administrator Registered: 2000-07-28 Posts: 11628 Loc: CA	Did this happen after a Microsoft Windows Update TUESDAY ? Was there an undocumented router change?
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#209864 - 2015-01-19 10:00 PM Re: Set mtu in Win7 [Re: GAW]
Arend_ Arend_ MM club member Registered: 2005-01-17 Posts: 1896 Loc: Hilversum, The Netherlands	Lonk: confuses me sometimes; ethernet spec is 1500, while IEEE 802.3 spec is 1492. GAW: probably some switch or firewall has an MTU < 1500, all switches and firewalls must be configured with the same MTU size.
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#209865 - 2015-01-19 10:47 PM Re: Set mtu in Win7 [Re: Arend_]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	arend, it does not really matter what the ethernet is. payload for encapsulated packets is less than the full length. if the software in question actually refuses fragmented packages, the only solution is to drop MTU lower. anyways, the last time I had to play with these was around 2009 or so. like I said, the data stored in my memory says this was "fixed" with vista and should not be an issue anymore. _________________________ ! download KiXnet
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#209866 - 2015-01-19 11:45 PM Re: Set mtu in Win7 [Re: Lonkero]
Arend_ Arend_ MM club member Registered: 2005-01-17 Posts: 1896 Loc: Hilversum, The Netherlands	Interesting though, I only had these types of problems when I introduced Jumbo Frames to my SAN. I had to put the switches to > 9000 MTU, whilst VMware components & drivers were exactly 9000 for it to work properly.
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#209867 - 2015-01-20 01:31 AM Re: Set mtu in Win7 [Re: Arend_]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	Exactly same issue, different software stack. _________________________ ! download KiXnet
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#209880 - 2015-01-26 03:32 PM Re: Set mtu in Win7 [Re: Lonkero]
GAW GAW Fresh Scripter Registered: 2010-02-16 Posts: 20 Loc: Tennessee	Just so I don't leave this hanging... The Network Engineers finally figured out what happened. Originally they thought the changes they made would not cause our problems even though it occurred at the same time their changes went live... hmmm Here is their final findings: What we learned: If a Cisco IOS router is configured with mtu x and is connected to a Cisco IOS XR router, then the corresponding interface on the Cisco IOS XR router should be configured with mtu x+14 for Ethernet interfaces, or mtu x+4 for serial interfaces. Cisco IOS and Cisco IOS XR software have the same meaning for the ipv4 mtu, ipv6 mtu and mpls mtu commands; they must be configured with the same values. You can use the command mtu 1514 or ipv4 mtu 1500.
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#209881 - 2015-01-26 04:06 PM Re: Set mtu in Win7 [Re: GAW]
Lonkero Lonkero KiX Master Guru Registered: 2001-06-05 Posts: 22346 Loc: OK	Nice. "it wasn't me" _________________________ ! download KiXnet
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