Re: can I ask mtu question
Which standard are you referring to? AFAIK, nothing above 1500 is standardised I've had two different kinds of customer requests for jumbo frames - customers that want very large frames for performance reasons; Many ethernet switches support 9000 or more, some don't, and some technologies like ATM support ~4470. Sometimes the ability to provide them depends on tunnel modes. - customers that want frames that are at least ~1700-1800 bytes so that a few layers of IPSEC or VLAN headers or whatever won't break the 1500-byte packets inside them. -- Thanks; Bill Note that this isn't my regular email account - It's still experimental so far. And Google probably logs and indexes everything you send it.
Re: can I ask mtu question
Ricky Beam wrote: On Fri, 30 Jan 2009 17:00:00 -0500, Saku Ytti saku+na...@ytti.fi wrote: Which standard are you referring to? AFAIK, nothing above 1500 is standardised None that have ever been accepted. From a quick google for manufacturer support, 9216 looks like the most popular number. But, as I said, it boils down to the largest frame *every* device on the LAN will accept. If there is a single device that only supports 9000, then that's your limit. And if there's a single non-JF device in the LAN, it throws a wrench into the whole thing. (This appears to be one of the sticking points as to why IEEE won't accept the addition of JF to any specs.) --Ricky PS: The topic pops up again with super-jumbo frames in 10G networks. For what it's worth, TCP will negiogate MSS and will work with mismatched MTU in a single LAN segment. Other protocols (e.g. UDP) will be borked though. S
Re: can I ask mtu question
* sam_mailingli...@spacething.org (Sam Stickland) [Tue 03 Feb 2009, 13:04 CET]: For what it's worth, TCP will negiogate MSS and will work with mismatched MTU in a single LAN segment. No Machine 1 -- switch with 1500 byte MTU -- switch with smaller MTU -- switch with 1500 byte MTU -- machine 2 Same situation as when you have IP routers with smaller MTUs in the path that also do not send ICMP Fragmentation Needed errors (or those are dropped on the way to you) If you configure one of those machines with an MTU equal to or smaller than the smallest MTU in the path then yes TCP (assuming MSS option is used) won't send packets that happen to be too big, but again, same story as for routers vs on a LAN. The problem isn't that machine 1 and 2 in the above example disagree on MTU, the problem is that equipment in the path disagrees on the MTU and cannot (in the case of switches) send notifications of such, or those will not arrive (in the case of stupid firewall admins in control of networks). -- Niels.
Re: can I ask mtu question
Niels Bakker wrote: * sam_mailingli...@spacething.org (Sam Stickland) [Tue 03 Feb 2009, 13:04 CET]: For what it's worth, TCP will negiogate MSS and will work with mismatched MTU in a single LAN segment. No Machine 1 -- switch with 1500 byte MTU -- switch with smaller MTU -- switch with 1500 byte MTU -- machine 2 Same situation as when you have IP routers with smaller MTUs in the path that also do not send ICMP Fragmentation Needed errors (or those are dropped on the way to you) If you configure one of those machines with an MTU equal to or smaller than the smallest MTU in the path then yes TCP (assuming MSS option is used) won't send packets that happen to be too big, but again, same story as for routers vs on a LAN. The problem isn't that machine 1 and 2 in the above example disagree on MTU, the problem is that equipment in the path disagrees on the MTU and cannot (in the case of switches) send notifications of such, or those will not arrive (in the case of stupid firewall admins in control of networks). Sorry, I should had clarified. I meant mismatched host MTUs within a jumbo MTU supporting L2 domain. Sam
can I ask mtu question
Hi What is max mtu in jumbo frame? ls it 9000? Do I need to reboot the switch to take effect after setting up it? if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? Thank you for your help Send instant messages to your online friends http://uk.messenger.yahoo.com
RE: can I ask mtu question
Depends on the hardware - GSR's have different MTU's than 7600's for example (and dependant on linecard too). We use 9216 between 7206VXR and 7606 for example. No, the change is immediate - show interface will tell you among other commands... Paul -Original Message- From: adrian kok [mailto:adriankok2...@yahoo.com.hk] Sent: January 30, 2009 12:57 PM To: nanog@nanog.org Subject: can I ask mtu question Hi What is max mtu in jumbo frame? ls it 9000? Do I need to reboot the switch to take effect after setting up it? if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? Thank you for your help Send instant messages to your online friends http://uk.messenger.yahoo.com The information transmitted is intended only for the person or entity to which it is addressed and contains confidential and/or privileged material. If you received this in error, please contact the sender immediately and then destroy this transmission, including all attachments, without copying, distributing or disclosing same. Thank you.
RE: can I ask mtu question
http://www.google.com/search?source=ighl=enrlz==q=What+is+max+mtu+in +jumbo+frame%3F+btnG=Google+Searchaq=f -Original Message- From: adrian kok [mailto:adriankok2...@yahoo.com.hk] Sent: Friday, January 30, 2009 12:57 PM To: nanog@nanog.org Subject: can I ask mtu question Hi What is max mtu in jumbo frame? ls it 9000? Do I need to reboot the switch to take effect after setting up it? if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? Thank you for your help Send instant messages to your online friends http://uk.messenger.yahoo.com
Re: can I ask mtu question
KanREN runs Foundry (Brocade) NetIron XMR 4000's as our primary core infrastructure with an MTU of 9216. To make the change (this is Foundry-specific), we have to change some system-max settings which only take effect once the device has been rebooted (or at least it DID require a reboot in the IronWare 3.3.x days). It does NOT reboot immediately so you're free to make the change then perform a reboot at a convenient time. -- Brad Fleming Network Engineer Kansas Research and Education Network Office:785-856-9800 x.222 Moblie: 785-865-7231 NOC: 866-984-3662 On Jan 30, 2009, at 11:57 AM, adrian kok wrote: Hi What is max mtu in jumbo frame? ls it 9000? Do I need to reboot the switch to take effect after setting up it? if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? Thank you for your help Send instant messages to your online friends http://uk.messenger.yahoo.com
Re: can I ask mtu question
On Fri, 30 Jan 2009 12:57:25 -0500, adrian kok adriankok2...@yahoo.com.hk wrote: What is max mtu in jumbo frame? That depends on the hardware. I've seen gear running as low as ~8k. I'd have to consult standard, but I think the max is 10k (10240). Keep in mind the switch is not the only device on the network with jumbo frame limits. The NICs in your servers will also have limits. Do I need to reboot the switch to take effect after setting up it? Again, this depends on the system. Many accept the change immediately, while others have to rebooted or interfaces reset to effect the change. if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? ping will do. Set the packet size larger than the normal MTU (1500) and see if it crosses the network intact. If it's not working, A) the packets will be dropped, and B) the oversized frame counter (among others) should be clocking errors. --Ricky
Re: can I ask mtu question
On Fri, 30 Jan 2009, Ricky Beam wrote: On Fri, 30 Jan 2009 12:57:25 -0500, adrian kok adriankok2...@yahoo.com.hk wrote: What is max mtu in jumbo frame? That depends on the hardware. I've seen gear running as low as ~8k. I'd have to consult standard, but I think the max is 10k (10240). Keep in mind the switch is not the only device on the network with jumbo frame limits. The NICs in your servers will also have limits. Do I need to reboot the switch to take effect after setting up it? Again, this depends on the system. Many accept the change immediately, while others have to rebooted or interfaces reset to effect the change. if it doesn't need to reboot, How can I know the switch is running fine in this mtu 9000? eg: cisco any tools to check? ping will do. Set the packet size larger than the normal MTU (1500) and see if it crosses the network intact. If it's not working, A) the packets will be dropped, and B) the oversized frame counter (among others) should be clocking errors. If you're sourcing the pings from a device that supports it, you can also send the large pings with the Do Not Fragment bit set. jms
Re: can I ask mtu question
That depends on the hardware. I've seen gear running as low as ~8k. I'd have to consult standard, but I think the max is 10k (10240). There *is* no standard for jumbo MTU. IEEE has steadfastly refused to standardize anything bigger than 1500 bytes. Steinar Haug, Nethelp consulting, sth...@nethelp.no
Re: can I ask mtu question
On (2009-01-30 16:33 -0500), Ricky Beam wrote: That depends on the hardware. I've seen gear running as low as ~8k. I'd have to consult standard, but I think the max is 10k (10240). Which standard are you referring to? AFAIK, nothing above 1500 is standardised -- ++ytti
Re: can I ask mtu question
On Fri, 30 Jan 2009 16:51:00 -0500, Justin M. Streiner strei...@cluebyfour.org wrote: If you're sourcing the pings from a device that supports it, you can also send the large pings with the Do Not Fragment bit set. Most modern systems do that already (part of path MTU discovery.) And if there are no routers in the path (only the switch in question), then there's nothing to fragment it anyway. --Ricky
