mixed gigabit and std ethernet network questions

I have a house wired with cat 6e. Right now I'm just using standard 10/100 ethernet, but I want to try to move to gigabit because I plan to get an Infrant readynas that suports jumbo frames. Unfortunately, not everything on the network can be upgraded to handle jumbo frames, or gigabit for that matter.

I'll try to describe the network as it is now.

cable modem-> VOIP box-> linksys wireless router WRT54G ... this is in the "office"

from the wireless router WRT54G:
port 1 thru 3 are to computers in the same room (2 athlons and an old P2)
port 4 goes to switch #1 in the closet
wireless is for a sempron notebook

from switch #1:
port 1 goes to a DVR in the Bedroom
port 2 goes to switch #2 in the family room (DVR and Roku soundbridge hooked to it)

Everything workds perfectly as is!

I have 2 wires in the wall from the wireless router to switch #1's location in the closet (only one used of course).... so with that in mind .........Here's what I want to do:

cable modem-> VOIP box-> linksys wireless router WRT54G (unchanged)

from the wireless router
port 1 goes to a new gigabit switch in same office
port 2 goes to old P2 machine the kids use for games (prolly should retire)
port 4 goes to switch #1. Everything downstream of that is the same
wireless still reserved for sempron notebook if roaming

from the gigabit switch
port 1 goes to Athlon 2500+ w/ Gb nic
port 2 goes to Athlon 1.3Ghz w/ Gb nic
port 3 goes to the sempron notebook with new gigabit adaptor
port 4 goes to the NAS in the closet next to switch #1.

I know everything downstream of the gigabit switch has to have jumbo frames enabled (no mixing jumbo and non-jumbo under the switch), but I'm concerned with the communications with the rest of the network.... specifically:
1. streaming music to the roku from the nas, 1000 (jumbo'd) ->100
2. eventually I want to stream video to other 100 devices
3. performance of moving files from the nas w/ jumbo frames to a wireless computer or even a 100 visitor that hooks to the router.

What other sort of issues may I encounter? Basically I want maximum file transfer speeds on everything under the Gigabit switch, but I don't want the network to hit a huge bottleneck and "stall" when streaming or moving files to a slower component or a wireless client. I know it will slow, but I don't want it grinding away and dropping packets like crazy and then timing out or something.

I can keep it simple and just put the NAS on the switch #1, but then I'd have slower xfer speeds (and I wouldn't learn anything either)

thanks in advance
4 answers Last reply
More about mixed gigabit ethernet network questions
  1. You really shouldn't have to worry so much -- path MTU detection should take care of jumbo / non-jumbo on a point-to-point basis. One of my key computers still doesn't support jumbo frames, so I've always mixed jumbo and non-jumbo frames configuration through the same switch.
  2. I figured that "under" the gigabit switch, all would be fine as long as everything was on jumbo frames (or not .. just as long as it was consistent). In this case, everything "above" the switch would be on the std ethernet, and the gigabit switch would "reconfigure" the MTU's back to 1500 to communicate with the remaining equipment. So.... would it be correct to assume that the switch buffers or regulates the data from the jumbo framed equip to the std ethernet equipment to reduce packet loss and congestion on the network (I'm not sure if I framed that correctly) ...

    I didn't think a giga switch would manage communications between a jumbo and non jumbo unit connected to it (I guess that's why I'm writing). I thought that affected performance negatively by having to constantly switch between the MTU sizes.

    thanks for the reply
  3. The switch doesn't really switch MTUs -- it just forwards them as they come in. Perhaps you're worried about fragmentation -- this doesn't happen, at least with this level of switch, because they aren't that smart --- the packets are sent out with the "best" size as determined by the path MTU protocol, and aren't fragmented in transit.

    I can tell you that I get very good performance in a mixed MTU environment here. E.g. up to ~950 Mb/s without jumbo frames, and up to ~990 Mb/s with (sustained synthetic measurements; actual file transfers are somewhat less of course.)
  4. I'll give it a shot .... thanks for the quick feedback.

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