Need help with Jumbo Frames

[Cool1Net6]

I am in need of some [H]ard networking knowledge. To ask my questions, it is easier to show my network topography:

My side of the network is 2 PC's, a laptop, a PS3, and a Wii. In the near future, I plan to revamp my home network; replacing the XP Server with a WHS box, moving all my data to WHS, and upgrading my computer and the switch to Gigabit. As you can see, I plan to have a mixed network of Fast Ethernet, Gigabit, and Jumbo Frame Gigabit devices.

I keep hearing that Jumbo Frames makes gigabit file transfers even sweeter, but I have several questions which my research can't clearly answer.

If I get a Jumbo Frame (JF) switch, can devices that are regular GigE coexist with JF-enabled devices? I heard that Megabit devices might not play nice on a JF GigE switch, but what if one port is used as an uplink to my router; will its packets get dropped?

Will this mixed network work, or do I have to divide things up into a three, distinct regions (which would suck)?

Thanks.

 

[Keiichi]

Basically you need to get a switch and netwrok cards that support jumbo frames. From there you would need to configure them for the appropriate jumbo packet size. Keep in mind that all devices involved with the packet transfer must support jumbo frames or the transfer will be knocked down to regular gigabit speeds.

 

[InvisiBill]

While most of the information I've found is a bit older, everything I've seen says that Jumbo Frames require their own VLAN or network segment.

http://sd.wareonearth.com/~phil/jumbo.html

How can jumbo frames and 1500 byte frames coexist?
Two basic approaches exist:

• On a port by port basis, where everything "downstream" from a given port is known to support jumbo frames.
• Using 802.1q Virtual LANs, where jumbo frame and non-jumbo frame devices are segregated to different VLANs.

http://www.networkworld.com/forum/0223jumboyes.html

In the past, users who demanded the efficiency of large frame sizes had to build separate workgroup networks. Today, however, applications optimized for large frame sizes can easily be integrated with existing Ethernet LANs without causing interoperability problems. For example, you can partition a logical network in which systems can exchange Jumbo Frames and mark them with IEEE 802.1Q virtual LAN tags. The extended frames will be transparent to the rest of the network.

Adapters that implement IEEE 802.1Q can support different Ethernet frame sizes for different logical network interfaces. For example, a server could communicate with another server using Jumbo Frames while communicating with clients sitting on another VLAN or IP subnet using standard Ethernet frames - all via the same physical connection.

http://www.beowulf.org/archive/2002-April/006940.html

Jumbo frames are great to reduce host frame procesing overhead, but,
unfortunately, we arrived at the same conclusion: jumbo frames and
normal equipment do not mix well. If you have a separate network where
all participants use jumbo frames, fine; otherwise, things get messy.

Alteon (a key proponent of jumbo frames) has some suggestions: define a
normal frame VLAN including everybody and a (smaller) jumbo frame VLAN;
then use their ACEswitch 180 to automatically fragment UDP datagrams
when routing from a jumbo frame VLAN to a non-jumbo frame VLAN (TCP is
supposed to negotiate MTU for each connection, so it should not need
this help). This sounds simple, but it requires support for 802.1Q VLAN
tagging in Linux kernel if a machine is to participate in both jumbo
frame and in non-jumbo frame VLAN. Moreover, in practice this mix is
fragile for many reasons, as Donald Becker has explained...

Some things could've been updated since all this was published. Devices might be better at auto-negotiating this stuff now. Networking is my weak point and I tend to get confused on what happens in which layers. The easiest way to deal with it is to have all your devices support Jumbo Frames, but I know that's not always possible. I don't know if the switches (i.e. your new GbE switch and the router's built-in 10/100 switch or the old switch) are smart enough now to fragment packets when needed and therefore you could use separate physical switches to segregate the haves and have-nots.

I too would love to learn more about this topic.

http://www.codinghorror.com/blog/archives/001232.html has some good info too. Read some of the comments at the bottom. One thing they point out is that the better the hardware gets, the less improvement there is from jumbo frames. Most also point out that there always seems to be something incompatible with jumbo frames and causing problems in a home network.

 

[Cool1Net6]

Well it seems from what InvisiBill posted that I will either have to get an expensive managed switch that can discriminate on a port by port basis, or get a degree in data communications to learn how to properly implement a 802.1Q VLAN, or run a completely separate network with a separate JF-enabled switch and separate JF-enabled NIC's.

All of this is more involved than what I am looking for. I guess I will keep things simple and just run regular GigE.

-Cool-