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Cisco 3560 & 4507 Jumbo Frames

I have a question about my current setup. I have an EMC ISCSI NAS device that I have connected to two 3560 GB switches, I have enabled jumboframes on the two switches. I also use the NAS function of the device and have an interface on the EMC configured for another network (VLAN8). I am gaining access to that network (VLAN8) via one of the fibre ports on the 3560 which maps back to a fibre port on my 4507. I have an MTU size of 9000 configured on all three interfaces (NAS interface, 3560 Fibre Int, 4507 Fibre int) my question is if I'll have issues with clients accessing the NAS since all my clients are obviously aren't using jumbo frames.

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Hall of Fame Super Bronze

Re: Cisco 3560 & 4507 Jumbo Frames

> my question is if I'll have issues with clients accessing the NAS

> since all my clients are obviously aren't using jumbo frames.

No. The client-to-NAS connection will send regular frame-size packets and makes no difference if jumbo frame is enabled in the switches. The problem you may encounter if you are sending jumbo frames in the client-to-NAS connection and the switches wouldn't support it. In the case, you would encounter packet fragmentation.

HTH,

__

Edison.

5 REPLIES

Re: Cisco 3560 & 4507 Jumbo Frames

HI Duhaas,

PC default frame size is 1472

VLAN will add 4 bytes

Total = 1472 + 4

So, VLAN8 having JUMBO Frame enabled will accept the packets upto 9000 bytes

Normally if NAS tries to contact a client with more than 1500 size means the packets should get fragmented before reaching PC's

Hope so its like the client-server setup and only the PC's will contact the NAS.

If the PC's are Windows Xp means no problem upto 1500 bytes. If it is Window 98 means make sure to check the size set in PC.

Hope i am Informative.

Pls rate if Helps

Best Regards,

Guru Prasad R

Community Member

Re: Cisco 3560 & 4507 Jumbo Frames

Just to be clear, I have the two fibre ports (one on 4507, one on 3560) configured for an MTU size of 9000, the reason I did that is that from what I have been told the 3560 MTU is a global switch setting, so I cant configure a port on the 3560 to be 1500 once I have enabled jumbo frames, hence I had to create an uplink port via fibre to my 4507 and set it to 9000 MTU. I just want to make sure that my clients wont have any performance issues accessing the NAS. Our network guys use solarwinds, and they are indicating to me that they are seeing many "HUGE BUFFER MISSES" and I dont know what to contribute it to. Not being a true networking guy, just trying to understand everything.

Hall of Fame Super Bronze

Re: Cisco 3560 & 4507 Jumbo Frames

> my question is if I'll have issues with clients accessing the NAS

> since all my clients are obviously aren't using jumbo frames.

No. The client-to-NAS connection will send regular frame-size packets and makes no difference if jumbo frame is enabled in the switches. The problem you may encounter if you are sending jumbo frames in the client-to-NAS connection and the switches wouldn't support it. In the case, you would encounter packet fragmentation.

HTH,

__

Edison.

Community Member

Re: Cisco 3560 & 4507 Jumbo Frames

So my interface on the NAS side should be set to 1500, the fibre ports between the switches (3560 and 4507) will be connected @ 9000, and clients will be connected @ 1500 and all will be well???

Hall of Fame Super Bronze

Re: Cisco 3560 & 4507 Jumbo Frames

Yes

__

Edison.

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