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Jumbo Frames and Internet access

July 7th, 2012

I recently added a Synology 411 NAS to my gear. Running in RAID 5 to have a good compromise between data safety and speed.

As easy as it is to set up such a NAS, to get it work in simple home network with full performance is less trivial.

My internet access is via a Netgear modem/switch. Sleak device that works perfectly with my 100Mbit fiber connection (thanks numericable).

Problem: Such switches are 100MB only, so the NAS attached via this switch tops out at 10Mbyte/sec - disappointing.

Solution: Get a Gigabit switch. I opted for a Netgear GS 605 which supports 9K Jumbo frames. So I cabled the modem, the NAS and my computer to the switch. Then I activated Jumbo frames 9k on my network card and on the NAS. Much better speed, around 35MByte/sec.

Not the end of the story: With these settings I wasn’t able to connect to facebook anymore, all browsers timed out. Facebook doesn’t like big frames. So to access FB I would have to deactivate Jumbo Frames again… Jumbo Frames might also impair performance of VoIP, etc. - the normal internet connection is set for MTUs of 1500 or even lower.

Solution: Get a second network card. If your computer already has a Gigabit Ethernet which supports 9K Jumbo Frames, get the cheapest you can find. The new card will become the internet gateway.

After installing the new card, connectit directly to the modem/router. This is important, because it will then run in 100MB mode. This will make Windows prefer the 1GB card if it can resolve a peer via that connection.

With this connection I got over 65MByte/sec from the NAS - good.

Last tuning step: Make sure that the GB connection will not be used for internet connections: Go the properties of the GB connection and select the IPv4 compenent and open its properties. Select using a fixed IP and enter an address like 192.168.0.201 and no default gateway. 201 is outside the DHCP range I configured in my router.

Now everything works as expected, hope this is helpful for you