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I recently purchased a Netgear GS108T managed switch and I am trying to configure jumbo packets between my NAS (Thecus N4100Pro), PC and managed switch. I should mention the fact that I was able to use jumbo frames between my PC and NAS before I purchased the switch without issue.

My Desktop has a wired gigabit NIC (Intel 82579V Gigabit) and has the ability to configure jumbo frames (see pic) that are either 9014 bytes or 4088 bytes. I choose 9014 bytes for the jumbo frame size

nic1

My NAS supports jumbo frames as well, and is configured to use 9014 as the frame size.

When I go into my Netgear managed switch and set the frame size to 9014 on the ports I am using for my PC and NAS. See image

Switch1

As soon as I hit apply in the web interface, I loose my connection to the SMB shares on my NAS and I can no longer connect to the web admin interface for my NAS. The really strange thing is I can ping my NAS via the ping command, but when I try to connect to the web interface on port 80 or port 443 the page never loads. I did a scan from my PC to my NAS using nmap and I can see the following ports open

PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
111/tcp   open  rpcbind
139/tcp   open  netbios-ssn
443/tcp   open  https
445/tcp   open  microsoft-ds
631/tcp   open  ipp
2000/tcp  open  cisco-sccp
2049/tcp  open  nfs
3260/tcp  open  iscsi
49152/tcp open  unknown
MAC Address: 00:14:FD:15:00:44 (Thecus Technology)

Read data files from: C:\Program Files (x86)\Nmap
Nmap done: 1 IP address (1 host up) scanned in 211.97 seconds
           Raw packets sent: 1 (28B) | Rcvd: 1 (28B)

Anyone have any idea what is going on here? Why is nmap able to detect the ports are open and listening for http, https and file sharing but I cant connect when all devices have jumbo packets enabled?

Stranger still - I did a packet capture using wireshark while the nmap scan was running and filtered so I only saw converstations between my PC and my NAS. Here are the packet details from my scan

packets

Only 4 packets over 5k bytes? What is going on here? Do I not need to configure jumbo frame sizes on the switch?

I have an internet connection from my pc to the switch to my router - I just cannot connect to my NAS. I just checked on my iPhone and I am able to open my NAS web admin interface without issue on my iPhone! WTF!!!!!!

Let me know if you need more details..

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Normally Jumbo Packets are a network-wide setting; you can't mix and match the MTU on each device on the same network. Your desktop and NAS are using 9014, but what happens when the NAS sends a 9014 sized frame to your phone that only has a 1500 MTU? Is there somewhere else in the switch management to enable Jumbo Frames perhaps? –  fukawi2 Dec 18 '12 at 3:44
    
this is - my phone CAN connect to the NAS web admin interface - only my pc seems to be having issues communicating. Not a bad idea to take a look at other places to configure jumbo packets in the switch tho.. Ill poke around a bit more. –  Richie086 Dec 18 '12 at 3:49
    
If the phone and NAS are only exchanging frames under 1500 (by chance) then there won't be a problem, but if the phone is expecting up to 1500 and the NAS sends frames over that, then you'll start getting strange things possibly. Regardless, the fact that it's normally a network-wide settings makes me think there's somewhere else in the switch to configure it. On HP ProCurves, it is a per-VLAN setting. –  fukawi2 Dec 18 '12 at 5:38

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