Jumbo Frames?

[sechs]

The more I read about this, the more confused I get. So, hopefully, someone here can set me straight.

Do all the devices on a LAN need to support jumbo frames for it to work?

Here's the situation:
I have LAN where the majority of the traffic runs between a few gigabit-capable devices. In order to improve throughput, I'm going to put a gigabit switch (the Netgear GS105, previously recommended here) between them, and then uplink it to the existing 100base-T router. Now, there should be plenty of boost just with the additional bandwidth, but I'm wondering if I can goose it a little more by turning on the jumbo frames.

A lot of what I've read on the 'net implies that all devices on the network need to support jumbo frames for it to work at all. Since everything downstream the switch (the router, 100base-T clients, wireless AP, DSL modem) won't run with the jumbo frames, if that's the case, it's not worth the effort.

 

[Stereodude]

My understanding is that devices that don't support Jumbo Frames still will work, but the switch is responsible for converting / breaking up jumbo frames. Apparently some switches do a very poor job of this, or bog down badly when doing so.

 

[ddrueding]

IIRC, you need a VLAN of some sort that will convert your jumbo frames to regular frames for other devices. Thats as far as my research got.

 

[P5-133XL]

My understanding is that devices that don't support Jumbo Frames still will work, but the switch is responsible for converting / breaking up jumbo frames. Apparently some switches do a very poor job of this, or bog down badly when doing so.

A switches job has absolutely nothing to do with converting/breading up frames. What a switch does is to simply read an address; decide which port it needs to travel; and then send it on its way. It does not manipulate the frames in any way ...

All devices within a network need to understand Jumbo frames. Vlans can define seperate networks and thereby can keep Jumbo frames seperate from devices that can't handle them.

Routers, that understand Jumbo frames, are the devices that convert/breakup frames. They are the devices designed to interface between networks and change protocols as necessary. You are not going to find a consumer-level router that will interface between jumbo frame networks and non-jumbo frame networks.

For most, the cheapest router that will do the job will be a server with multiple network cards and routing capability. That way you can define the jumbo-frame network on one network card and the non-Jumbo frame network card and then have the server operate as the interface between them ...

 

[ddrueding]

Thanks Mark. You don't happen to know what a/the cheapest router capable of doing such a trick, would you?

It would be too easy if this baby supported it...

 

[P5-133XL]

I know you can do it on Cisco routers by simply changing the MTU on the different interfaces. Other than that, I don't know of any. But then I haven't really researched it ...

 

[sechs]

To be clear, if I take all of the devices on the gigabit switch and turn on jumbo frames, I will get exactly nada?

 

[Stereodude]

To be clear, if I take all of the devices on the gigabit switch and turn on jumbo frames, I will get exactly nada?

I tried it before and the network still worked. It didn't work well and I turned them off, but...

 

[Stereodude]

A switches job has absolutely nothing to do with converting/breading up frames. What a switch does is to simply read an address; decide which port it needs to travel; and then send it on its way. It does not manipulate the frames in any way ...

What about a layer 3 switch? As I understand it a Layer 3 switch is basically a router implemented in hardware rather than software running on a processor.

 

[P5-133XL]

What a layer-3 switch does is read IP addresses, instead of the MAC address, and use that data to decide what port to send the data.

A layer 3-4 switch will sometimes do a primitave QOS and prioritize the packets (i.e. reorder them in a queue) before sending them on their way.

A layer 4-7 switch will read content, for load balancing purposes, and then send the packets on their way ...



What none of the switches do is reformulate or manipulate the contents of the packets which is what would be needed to convert a jumbo packet to a non-jumbo form. That is the exclusive domain of routers and/or bridges.

 

[P5-133XL]

To be clear, if I take all of the devices on the gigabit switch and turn on jumbo frames, I will get exactly nada?

If not all the devices on a network can deal with jumbo frames and you activave jumbo frames then what will happen will be lost frames and lots of requests for re-transmittal. The net result will be time-outs and very low performance.

 

[Stereodude]

So, what is the proper way to make it all work?

I have a wireless router that only has 10/100 capabilities for it's wired ports. All my "desktop" PCs (3) have gigabit Ethernet and support jumbo frames. However, they all need at least internet connectivity through the 10/100/wireless router. I also have two notebook PCs (neither has gigabit) that occasionally need to access data on 2 of the 3 desktop PCs as well as print to the printer connected to one of the desktop PCs (generally through wireless). I also have a Roku Soundbridge (stand alone media player device) that only has a 10Mbit connection and accesses data on one of the desktop PCs. Without some sort of "bridge" device that supports jumbo frames & gigabit on the one side and standard 10/100 on the other I haven't a clue how to make this all work and have the 3 "desktop" PCs talk to each other via jumbo frames. I could make a VLAN with just the 3 "desktop" PCs, but then they wouldn't be able to access the internet, or have any of the other devices access them, so that's out as an option.

 

[Mercutio]

The easiest thing, I found, was just to set up a second network.

 

[Stereodude]

The easiest thing, I found, was just to set up a second network.

Can you explain a little bit more? Did you put a 2nd NIC in each PC to have two separate networks? Do your two networks talk to each other?

It would seem that setting up two VLANs with some sort of bridge between them would be the best course of action. However, a Cisco 2800 series router seems a little extreme for a bridge. I would guess a PC with two NICs and linux could do the job...

 

[P5-133XL]

Either take one of your PC's or get another one. On that PC, Put on Windows Server or Linux and use two network cards. On the first Gigabit network card, enable jumbo frames and connect it to the Gigabit switch; Enable Jumbo frames for all the other PC's that are attached to it.

On the second network card (10/100) attach it to a 10/100 switch/router. Attach all your 10/100 stuff to it.

The two network cards will need to be on seperate IP networks and you will have to enable the routing capabilities of the server to communicate between the two networks.

If you need to file-share across the two networks, then the prefered way is to use a domain controller and use DNS as your master browser. The other convienant setup is to place all your files on the server itself and just share off it because it has direct access to both networks.

On the server, you will have to set up routing to allow data to pass between the two networks. You will also need to set gateway addresses that point to the server's IP address. On the server, you will need to set its gateway addresses to cross the networks (the Gigabit interface needs to point to the 10/100 and the 10/100 needs to point to the router).

For the PC with the media player, you will need to give that PC a second network card (10/100) to attach the media player. It will also get a seperate network. Or to make it easier, place the media player on the 10/100 side of the server and place the media files it needs access to on the server.

Your printer can be attached to any PC, just make sure that it is advertised using the domain.

Is all this really worth it, just so you can use Jumbo Frames?

Did I cover everything? Any mistakes (anyone)?

 

[Mercutio]

That's pretty much what I did, Mark.
In my case, the original reason to build the separate network wasn't to use jumbo frames, it was because I didn't want to buy a 16-port gigabit switch.

 

[P5-133XL]

Also, all your PC's and notebooks need to be able to join the domain: No XP Home, unless you share everything off the server (including the printer) so that no one needs to cross the network boundry to file share. If everything belongs to the domain, then you can cross the network boundry for file sharing.

Basicly, workgroup file sharing (XP Home) uses master browsers to communicate what resources are availiable that uses broadcast packets and they won't cross a network boundry. With the Domain, it will use DNS and thereby can cross the network boundry.

 

[ddrueding]

I don't see any errors in your layout Mark. It is a mess of work, that's why I now have local storage for all my goodies.

 

[Sol]

If the server is also the networks NAT router and the file server then life becomes much easier. Since it's already everyone's default gateway you just add a routing rule for each network (probably automatically added actually).

Sharing stuff from one network to the other should be fine it's just browsing that would be a problem so just typing in the address of the PC with the share or mapping a drive to it would work fine (I always do one of these because it's so much quicker than browsing once your used to it).

 

[sechs]

If not all the devices on a network can deal with jumbo frames and you activave jumbo frames then what will happen will be lost frames and lots of requests for re-transmittal. The net result will be time-outs and very low performance.

Frankly, that seems backwards. I would have thought that the worst case scenario is that everyone negotiates down to the lowest common denominator, which, in this case, is standard-sized frames.

Obviously, my networking knowledge is lacking in this department, but why don't devices determine this stuff on a bilateral basis, i.e., on the same network, jumbo-capable devices talk jumbo-speak to one another and regular frames to non-jumbo-capable devices?

 

[sechs]

Also, all your PC's and notebooks need to be able to join the domain: No XP Home, unless you share everything off the server (including the printer) so that no one needs to cross the network boundry to file share. If everything belongs to the domain, then you can cross the network boundry for file sharing.

Basicly, workgroup file sharing (XP Home) uses master browsers to communicate what resources are availiable that uses broadcast packets and they won't cross a network boundry. With the Domain, it will use DNS and thereby can cross the network boundry.

How would this work with Linux/Unix?

What about using WINS service rather than a domain?

 

[Stereodude]

Is all this really worth it, just so you can use Jumbo Frames?

Sure doesn't sound like it!

 

[P5-133XL]

How would this work with Linux/Unix?

What about using WINS service rather than a domain?

First, WINS is a broadcast protocol that won't cross a network boundry. If you want to use WINS, then put all your data on the server and share from that point. You won't be able to browse between the PC's and the notebooks (across the network boundry), but everything will be able to see the server. That also includes the printer: To be seeable to everything, the printer has to be hanging off the server. This also has the benefit of not requiring a domain and not requiring XP Pro on all the client PC's: Just use the same workgroup for everything...

With Linux/Unix, you would configure SAMBA and it can be setup as a domain controller or as a workgroup using WINS, just like above. You would also still have to configure the Linux/Unix server to route between the network cards.

 

[Mercutio]

My "server" PCs - the ones on my gigabit network - have static IPs, so even using a hosts or lmhosts file works fine, and both those things work in Windows and Linux. I have BIND set up properly to allow for dynamic hostnames but frankly on a home network that's more of a hassle than just making and distributing a hosts file.

 

[P5-133XL]

Sure doesn't sound like it!

On my own personal network. I have two pods of 4 computers each attached to gigabit switches. The two pods communicate to each other, and the internet router wirelessly using 802.11g access points. My main printer is an IP printer attached to the router.

I have occasionaly considered doing this to each pod but it never seems to be worth the effort. It would take hours (especially including the debugging and testing time) and the amount of saving from the increased gigabit speed would be minimal. The practical inside me says no and the astetic within me says yes because everyting would run better ...

Just like the conflict within me because I have access to an unsecured wireless network that I could so easily tap into and quit paying for my own internet connection. The practical says why pay for something you don't need to and then my ethical side says that would be stealing. So far my ethical side has always won and on the other issue, the practical side has always won. It doesn't mean the temptation is not ongoing for both ...

 

[Stereodude]

Just like the conflict within me because I have access to an unsecured wireless network that I could so easily tap into and quit paying for my own internet connection. The practical says why pay for something you don't need to and then my ethical side says that would be stealing. So far my ethical side has always won and on the other issue, the practical side has always won. It doesn't mean the temptation is not ongoing for both ...

Find out whose it is, offer to help them secure it, and find out if they'd be willing to split the cost and the BW with you. Then get rid of your connection.

 

[sechs]

So, the only way to do this is setup a bridging router?

This whole physically *and* logically separating the clients is nigh ridiculous, and totally not worth the effort. It doesn't seem like very many people would actually implement jumbo frames.

 

[ddrueding]

The last time I did it was because I used the same server for file/print serving and routing. Since I switched from MS ISA to smoothwall, I haven't looked back.

 

[P5-133XL]

So, the only way to do this is setup a bridging router?

This whole physically *and* logically separating the clients is nigh ridiculous, and totally not worth the effort. It doesn't seem like very many people would actually implement jumbo frames.

A Jumbo-frame Vlan switch would eliminate the need to physically seperate the networks: But you would still need the bridging router to communicate between the two logical networks. If you can get all your equipment Jumbo-frame compatible, then you don't need to seperate anything at all: The big problem here, for most people, is the internet router/firewall.

Until consumer-level jumbo-frame gigabit routers are common, you are right that very few people will be implementing jumbo-frames on their networks. Even, I, as a person totally capable of setting it properly, have a really hard time justifying doing it. For an amature: unthinkable. It is a massive hassle; costs signifigent $$$; makes your network less reliable and much harder to diagnoise problem because it is that much more complex (For someone that really doesn't fully understand whats going on, it can be pulling out hair time). On the up side the gigabit Lan is signifigently faster ...

 

[P5-133XL]

The last time I did it was because I used the same server for file/print serving and routing. Since I switched from MS ISA to smoothwall, I haven't looked back.

I pulled my smoothwall router because I ran into two problems. One was a specific IIS challange-response box that wouldn't get through the smoothwall and I could not see why. I needed to be able to logon and it wouldn't get through (other challange-response sites worked fine: It was specific to this one site). The second was ATI's guide+. Both of these, worked fine through MS proxy server and a standard firewall/proxy but would no go through the smoothwall box.

 

[sechs]

For grins, I looked for a consumer-SOHO appropriate wired gigabit router and only found a model from Dlink aimed at overspending gamers. Everything else in also an 802.11n AP, which is a completely unnecessary function in most cases.

 

[ddrueding]

So n functionality is a bad thing? Doesn't it make sense that devices that support cutting-edge wired connections (GbE w/Jumbo Frames) would also support cutting-edge wireless?

 

[P5-133XL]

For grins, I looked for a consumer-SOHO appropriate wired gigabit router and only found a model from Dlink aimed at overspending gamers. Everything else in also an 802.11n AP, which is a completely unnecessary function in most cases.

If it supports jumbo frames, it will be cheap (almost regardless of its price)compared to alternative solutions. As a brand, I really don't like D-Link though: but if it's the only choice ...

 

[sechs]

First, 802.11n isn't final.

Second, for most people, it's totally unnecessary.

Finally, it's added complication, i.e. makes the device more likely to fail.

Personally, I have WAP that works fine and does what I want.

 

[ddrueding]

#s 1, 2 & 4 don't make it bad; simply unnecessary. I think #3 is arguable, considering it's likely the same number of ICs in the device, just a different one that supports n as well.

 

[sechs]

Also, they cost more.

 

[Stereodude]

Correct me if I'm wrong, but couldn't you use 802.1q / VLAN trunking to put the gigabit machines onto both VLANs so they can both talk amongst themselves on the gigabit only network and so they can also talk to the non gigabit network?

 

[Mercutio]

You can if you have hardware that supports that sort of thing.
I assure you that you aren't getting that shit at Best Buy.

 

[Stereodude]

You can if you have hardware that supports that sort of thing. I assure you that you aren't getting that shit at Best Buy.

I'm not 100% sure, but it seems that most gigabit NICs support 802.1q. On the switch side, I'm sure the Best Buy flavor doesn't. However, the gigabit Linksys SRW series does, and they're not that pricey.

 

[P5-133XL]

Correct me if I'm wrong, but couldn't you use 802.1q / VLAN trunking to put the gigabit machines onto both VLANs so they can both talk amongst themselves on the gigabit only network and so they can also talk to the non gigabit network?

No that is not what a vlan does, it will prevent communication to and from the different vlan's so that the non gigabit and the gigabit networks can not communicate to each other. You will still need to connect the two virtual networks via a router.

A vlan creates seperate virtual lans on the same physical network. It is as if they were on seperate physical networks, but they are not. As such, you still need a router to communicate between them.