jeremymacmull

Gigabit Switches

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Isn't that what path MTU is solving?

193686[/snapback]

Well, I don't get it then. Did a bit of a google and it sounds like that's what it's about. So I don't know why the general consensus seems to be that technology such as VLAN is required to mix frame sizes. Just can't seem to find a conclusive answer anywhere.. :angry:

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Perhaps because it doesn't have wide implementation yet? Just a guess.

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Isn't that what path MTU is solving?

193686[/snapback]

Well, I don't get it then. Did a bit of a google and it sounds like that's what it's about. So I don't know why the general consensus seems to be that technology such as VLAN is required to mix frame sizes. Just can't seem to find a conclusive answer anywhere.. :angry:

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Thats because it is the only compliant way of sorting frame sizes between what are essentially two completely different media types.

Any properly implemented FastE switch will discard oversized frames, so relying on what are essentially propertiary hacks to use jumbo frames wont work.

PMTU discovery is a layer 3 service. See RFC 1191 for more detail as to how it works and it'll become obvious why.

The easiest and cheapest way to do this is get a S/H managed gig-e switch from ebay. Partition it into two VLANS and run a *single*, yes I said single gig-e trunk from your gateway server into it.

VLAN trunking and PMTU on the gateway will take care of the rest.

http://darkwing.uoregon.edu/~joe/jumbo-clean-gear.html

greg

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PMTU discovery is a layer 3 service.

193730[/snapback]

This is what I thought, but the information I read didn't specifically state it, and I only have a basic understanding on the network model so I wasn't sure.

After reading the RFC 1191 document you suggested (well, half-read as a lot of it went over my head) I can see that PMTU appears to define from one specific host to another specific host. What I (and I think many others that have discussed this before at SR) still don't quite grasp is this..

If you have a switch that supports jumbo frames and you introduce a non-jumbo device, why does the switch need to run in non-jumbo mode? PMTU discovery suggests that the jumbo capable devices can discover that communication to the non-jumbo device supports smaller MTU only. The non-jumbo device will only try and use a smaller MTU to begin with, which the jumbo capable device should be able to accept. There's a piece of information missing that must explain it. Maybe it's in cmkrnl's previous post, but I still don't get it..

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PMTU discovery is a layer 3 service.

193730[/snapback]

This is what I thought, but the information I read didn't specifically state it, and I only have a basic understanding on the network model so I wasn't sure.

After reading the RFC 1191 document you suggested (well, half-read as a lot of it went over my head) I can see that PMTU appears to define from one specific host to another specific host. What I (and I think many others that have discussed this before at SR) still don't quite grasp is this..

If you have a switch that supports jumbo frames and you introduce a non-jumbo device, why does the switch need to run in non-jumbo mode? PMTU discovery suggests that the jumbo capable devices can discover that communication to the non-jumbo device supports smaller MTU only. The non-jumbo device will only try and use a smaller MTU to begin with, which the jumbo capable device should be able to accept. There's a piece of information missing that must explain it. Maybe it's in cmkrnl's previous post, but I still don't get it..

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PMTU opperates at a level 3, which is higher then ethernet, which is level 2. If you turn Jumbo frames on at level 2, all frames sent by the ethernet card will be 9000 bytes long, regardless of the length of the data in the packets. Thus, the receiving device which doesn't accept jumbo packets will overrun with each packet and drop it.

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However, I returned this SMC switch b/c it was making high-pitched sound that was driving me nuts.
Possibly a bad capacitor. If you were to ask for a replacement, it is unlikely the new unit would have the same problem. My SMC switch makes no such noise, but I've seen that problem on cheap monitors (e.g. Optiquest) and narrowed it to a capacitor.

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My SMC switch...

I've been thinking of buying one of these from a US dealer as they are not available in Australia at anywhere near the prices available over there. Can you tell me if the AC adapter is universal (ie. supports up to 240v)?

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I can see that PMTU appears to define from one specific host to another specific host. 

Not quite, PMTU works on a hop by hop basis on the route between two hosts on different networks.

As the packet crosses each hop it'll be resized accordingly to fit ever is the largest acceptable frame size on the other side.

PMTU provides a mechanism to tell the sender what the largest acceptable size will be along the entire route to facilitate communication.

Interesting presentation here which

http://www.ncne.org/training/techs/2003/02...files/frame.htm

gives you some idea of the issues.

If you have a switch that supports jumbo frames and you introduce a non-jumbo device, why does the switch need to run in non-jumbo mode?

Because as 'rugger' explains above, everything on the switch is on the same network at Layer 2. The endpoints have no mechanism to figure out what is the largest Frame size the other end can accept.

Greg

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My SMC switch!

Port 1 = Server with Intel 1000MT 1000Mbit Jumbo Frames

Port 2 = HP print server 10Mbit

Port 3 = Game Machine 1 Realtek 1000Mbit Jumbo Frames

Port 4 = Game Machine 2 Realtek 1000Mbit Jumbo Frames

Port 5 = Wifes Computer Realtek 1000Mbit Jubmo Frames

Port 6 = Daughters computer Realtek 1000Mbit Jumbo Frames

Port 7 = Dell Laptop 100Mbit

Port 8 = Linksys Router

Everything works great except when I try to go to my web site hosted on my server. It tries to go though the router and it doesn't support jumbo frames. The fix is to add a line in the "c:\windows\system32\drivers\etc\hosts". I just have to make the web site redirect directly though my local network instead of my wan connection. No need for Vlan! Just Plug and Play :)

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Hello all,

A little introduction about myself. I work for a networking company (unfortunately I cannot give you the name). We make network controller IC for both server and desktop platform.

I have been reading a number of posts and I hope I can clarify a number of things for everyone here.

Jumbo frames was invented by Alteon back in the days of 10/100Mbit Ethernet. At the time, it was felt that an increase in the MTU size (from maximum of 1518 to 9K) would be of great benefits in data transfer.

I have been in this industry for 9 years and along with my colleages we all agree on one thing: Jumbo frames is a curse. It forces everything connecting to it support it, otherwise things don't work. Even to this day everything we built we have to support it even in environment that don't uses it.

So to clarify for a number of people. If you truly want to use Jumbo Frames, everything connected to it must support Jumbo Frames. Otherwise, once data is initiated, the data stream would automatically adjust the MTU size and finally the MTU got set back to 1518 anyway.

But I digress. Here is my current setup. Netgear Gigabit Ethernet Switch connected to 2 computers. One computer is using a Gigabit Ethernet Card made by Netgear, with a Realtek chip. The other computer is using Intel Gigabit LOM (Lan on Motherboard). The data transfer rate (copying large DVD files) varies between 190Mbit to 250Mbit. CPU utilization is around 30%.

The MTU size is from 1400 to 1518.

Okay here is the thing ive wanted to have a gigabit ethernet network for some time now

all the computers have gigabit ethernet capability and after looking at the prices of some switches i thought why not

the computers are

1 X A64 3200 with 160 gb (2X hitachis 7K250 in Raid 0) (2X 160 gb Hitachis in RAID 0 ) with and onboard gigabit network interface on asus K8V deluxe

1X A64 3400 with onboard Gigabit network interface with (2X samsung spinpoint 80 gb in RAiD 0) ASUS K8V deluxe

1X P4 3.2 with HT (1 X 74 gb raptor ) & (2X 7K250 80 gb in RAID 0) INTEL 875p chipset with CSA for ethernet

all the files pretty much that i want to move about are single large files ie more than 4000 mb often dvd size (dvd images to be exact) so i included disk setups as i thought in this case linear sequentual read and write performance could become a bottle neck due to the fact that im copying large files from pc A to pc b and c. i stress these are my mates computers and we live in a shared house so i dont really want a discussion about advantages etc etc of RAID 0  at all. all the raid systems can do 80 mb sec according to bechmarks so they should be able to get the maximum thruput without being disk limited too much

ive already got cat 5 e cabling in place although at the moment im using a linksys bef8r1 router and switch combo attached to my cable modem. which limits us to 100mbit speeds i was going to buy one of these gigabit swtiches and place all our computers on it after attaching it to the router to keep the internet connection

i know ill have a speed up in file transfers and i know what to realistically expect as a minimum but i was hoping with RAID 0 and the serial nature of large file transfers i would like to maximise that speed possibility by choosing the best switch for the money

the reason i ask questions is all the switches are very similiar in price and there are two from linksys and i cant tell the difference between em at all just the 5 pound diff in price and different shape!!??

OK ive blabbed on enough  here are my choices of switches

1) D-Link DGS-1005D 5-Port GigaExpress Switch 51 pounds

2) Linksys EG005W Gigabit 5-Port Switch 62 pounds

3) Linksys SD2005 5-Port Gigabit Switch 66 pounds (2 and 3 are the ones i cant tell the difference from and linksys are my preferred manufacturer but if there is a marked difference in speed then im willing to use another)

4) Netgear GS105 5 Port Gigabit Switch  55 pounds

5) US Robotics USR997930 8-Port Gigabit 60 pounds

6) Asus GigaX 1105 Gigabit Switch 43 pounds

ok thats it the price difference is inconsequential as at most its only about 10 to 20 pounds and im quite willing to spend the 66 pounds of the most expensive one so im not interested in that comparison. the only thing id like is a pure performance comparison

all those with experience with these switches pls contribute it would be appreciated

ive looked up reviews and benchmarks for the linksys EG005W switch and they say wildly different things on has a transfer of 49 mb sec other has 29 etc etc

JEREMY

191963[/snapback]

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It's been a few months since this thread was going, so I thought that I'd add to it.

The consensus appears to be that you need a switch that supports VLANs in order to adequately support a mix of jumbo and non-Jumbo frames. I doubt that we'll be able to walk into a computer store and just buy one of these today, but with prices coming down maybe there is something new online that is reasonably priced. ("Reasonable" being different for everyone of course.)

It looks like the SMC switch, which is still the only one <$100 supports Jumbo frames. But, we have mixed opinions on whether the NICs will cut back to non-jumbo on the fly, or just stay non-jumbo.

I agree with bigdn though, this is a curse in a way. :) Kind of like when 100BT came out, you had hubs with 100BT and 10BT, but switches that supported both were too expensive for most.

How do you set up a VLAN anyway? Do you need separate DHCP servers on each "network" then and the switch sorts by IP address or is it not complicated at all? If it's not bad, maybe it's time to check out the newer line of switches.

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Alternatively, I guess you could just get the absoulte cheapest non-jumbo gigabit switch today, and then use it as a backup when someone figures out how to integrate the two into one cheap switch. :)

EDIT: The SMC is still tempting to try though, might be good for future all-jumbo connections to other switches.

Edited by Krusher

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Alternatively, I guess you could just get the absoulte cheapest non-jumbo gigabit switch today, and then use it as a backup when someone figures out how to integrate the two into one cheap switch.  :)

EDIT: The SMC is still tempting to try though, might be good for future all-jumbo connections to other switches.

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The 16 & 24 port versions of the new Dell 27xx switch range have both vlan and Jumbo frame support.

http://www1.us.dell.com/content/products/c...s=04&l=en&s=bsd

http://www1.us.dell.com/content/products/p...s=04&l=en&s=bsd

Dunno WTF they disabled jumbo support in the 8 port one. I assume they are based on all the same switching hardware.

Greg

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You definetely need to get a jumbo frame supporting switch. Since you want to do file copies, this is ESSENTIAL for you. W/O jumbo frames, you will only get a modest -if at all- improvement. All your NIC should support it anyway.

192155[/snapback]

My switch does not support jumbo frame and I am traffering data at over 50MB/s, the limit here is my disk speed.

OS optimization and disk speed paly more important roles than jumbo frame. Jumbo frame can reduce cpu load but it also depends on nic since high end nics have tcp off-load.

I'm RAID system on both my server and workstation, and I'm also getting a jumbo frame supported switch, I'll post performance data when everything is here.

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Hope this isn't considered hijacking, but it seems like an appropriate place.

I would greatly benefit from having a gigabit ethernet connection between my main workstation and my fileserver which sit right next to each other. Could I buy 2 gigabit ethernet nics, hook them up with a crossover cable, direct all traffic to the file server from the workstation to the gigabit nic through the use of a hosts entry and have a working setup?

Thanks,

Chris

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Hope this isn't considered hijacking, but it seems like an appropriate place.

I would greatly benefit from having a gigabit ethernet connection between my main workstation and my fileserver which sit right next to each other.  Could I buy 2 gigabit ethernet nics, hook them up with a crossover cable, direct all traffic to the file server from the workstation to the gigabit nic through the use of a hosts entry and have a working setup?

Thanks,

Chris

206057[/snapback]

This will work.

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Has anyone used the Dell 2716/2724? I'd like to know if they have cooling fans in them. I want to replace a 3COM Baseline 10/100/1000 switch in my wiring closet -- it's so loud I can hear it across the house.

What about the SMC, is that one fanless?

I'm pretty unimpressed by my Netgear FS108 except that it's got a cool metal case.

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I read through the Del 27xx manual. The 8 and 16-port switches are fanless. The integrated power supply is a nice touch. Overall it looks like it is going to be difficult to beat the price/performance of these switches, at least while they are on sale.

I ended up ordering the 2724. It does have one fan. I can't believe I got a 24-port managed 10/100/1000 switch with vlan, jumbo frame, tos, link aggregation, etc., etc. for under $300 after tax and shipping. I'll report back when I get it, which should be 1st week of June.

I'm still interested in replacing my Netgear with an SMC, as long as it's fanless.

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Damn the American Dell deals :( . You guys don't know how lucky you are.

Sometimes I wonder if many Canadian geeks consider moving to the United States just for the Dell deals.

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