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MTU Sizes Jumbo Frames
I have a few questions on how the PowerConnect 6248 handles MTU sizes:
1. It appears if I have a host using jumbo frames at 9000 MTU then I have to use a MTU of 9216 to match?
2. I can apply a MTU size under a VLAN using the "ip mtu" command but I can't set it to 9216 since I get an error back saying "Value is out of range. The valid range is 68 to 9198." I understand why since 9216 isn't even a valid standard for jumbo frames. So is the MTU size on the port vs VLAN suppose to be different to support a MTU of 9000?
3.Do I have to apply a MTU size to a VLAN? My intent is not all VLANs on the physical port need jumbo frames.
Anonymous
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October 6th, 2014 12:00
Older firmware revisions had a lower maximum mtu size. In the newer revisions they increased the mtu limit.
It should let you set it to 9216. Can you post up the output of the command ,console>show version. This will let us check what revision the switch is on, which image the revision is installed on, and if that image is active.
You could also run the command [tag:iscsi] enable
When iSCSI is enabled, the following actions occur:
• The MTU on all ports and port-channels is set to 9216 (jumbo frames are
enabled).
• Flow control is globally enabled, if it is not already enabled.
• iSCSI LLDP monitoring starts to automatically detect Dell EqualLogic
arrays.
Anonymous
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October 6th, 2014 12:00
Sounds like the switch is on an older firmware revision. Getting the firmware up to date should enable the larger MTU setting.
http://dell.to/1vHRJit
PowerConnect48
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October 6th, 2014 12:00
I don't understand your response of:
1. "Getting the firmware up to date should enable the larger MTU setting."
9216 MTU is not even in the Ethernet Jumbo Frame standard, so why would it support larger?
2. I'm on the latest firmware A36, so no changes have been made to this release.
PowerConnect48
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October 6th, 2014 13:00
Daniel -
Would you mind reviewing my initial questions as I don't believe you fully understand them. See below on my firmware.
console#show ver
Image Descriptions
image1 : default image
image2 :
Images currently available on Flash
--------------------------------------------------------------------
unit image1 image2 current-active next-active
--------------------------------------------------------------------
1 3.3.11.2 3.3.4.1 image1 image1
Anonymous
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October 6th, 2014 13:00
Thanks for the output from the show command, it looks good.
With MTU size you need to leave enough room for the headers to be added. IPv4 =20, TCP =20, icsi can vary, etc. So MTU 9216 is not required, but is used to ensure there is enough space.
However with the firmware the switch is on should allow the mtu to be set to 9216. I just connected to one we have in the lab and it allowed me to set a port to 9216.
If you enter an interface and enter this command # mtu ?, what does it show as possible options?
PowerConnect48
41 Posts
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October 6th, 2014 13:00
Daniel
You are referring to a physical port. Please see below, I am referring to a VLAN interface.
2. I can apply a MTU size under a VLAN using the "ip mtu" command but I can't set it to 9216 since I get an error back saying "Value is out of range. The valid range is 68 to 9198." I understand why since 9216 isn't even a valid standard for jumbo frames. So is the MTU size on the port vs VLAN suppose to be different to support a MTU of 9000?
3.Do I have to apply a MTU size to a VLAN? My intent is not all VLANs on the physical port need jumbo frames.
Anonymous
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October 6th, 2014 14:00
I apologize, I was reading that incorrectly. With ip mtu on the VLAN interface, this value includes the 802.1q tag, but does not include the Ethernet header and CRC trailer. So, the maximum Ethernet frame size, including the Ethernet header/trailer, is 9198 + 18 = 9216 bytes.
The physical interfaces includes everything, meaning you can set it to 9216.
PowerConnect48
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October 7th, 2014 07:00
OK so back to question
3.Do I have to apply a MTU size to a VLAN? My intent is not all VLANs on the physical port need jumbo frames.
Anonymous
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October 7th, 2014 08:00
ip mtu setting is used when a packet is sent on an interface. When applied to a VLAN interface, the ip mtu command will be followed when the VLAN sends the packet to another VLAN. So if your jumbo frames are all staying in the same VLAN, then you shouldn't need to worry about it. However if the jumbo frames will frequently be moving from VLAN to VLAN, i would set the ip mtu to 9198.
PowerConnect48
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October 7th, 2014 10:00
"i would set the ip mtu to 9198."
To be clear, on a host with a MTU of 9000 you're saying on the VLAN interface that would equal 9198 on your switch? That is odd but let me know if that is what you're saying.
Anonymous
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October 7th, 2014 11:00
yes, on a VLAN interface you would set it to 9198.
On the physical interface you would set it to 9216.
simomemtro
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September 14th, 2017 06:00
Hi
I have a question please. i dont have acces to my actual fabric switch 2748 and i am waiting for a powerconenct 7048 switch that i need to set it as a fabric switch. on my hosts and SAN eqaullogic Ps6100 i have the MTU set at 9000. what Mtu should i give to my Dell 7048 ? 9000 or 9219 ? and whay ?
many thanks
Henning1
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October 26th, 2017 05:00
Hello,
here you find the best-practice configuration for a lot of switches and different Dell-SANs.
[View:~/techcenter/storage/w/wiki/4250.switch-configuration-guides-for-ps-series-or-sc-series-sans:550:0]
Among them is the PC7048: http://en.community.dell.com/techcenter/extras/m/white_papers/20438529/download.aspx
regards
Henning