Most Important Jumbo Frame Question!

[JEEPMON]

I am sure this is the most common and popular setup and a very important question. Say you have several computers in your house all hard wired (ethernet)up through a wireless router that is connected to a modem (DSL or Cable) to the internet. There is also a NAS or a home server for sharing, backups, and storage. All of the computers support jumbo frames as well as the router and the NAS. I can see how jumbo frames would help if enabled, for transfers to and from the computers and the server/NAS. BUT will enabling the jumbo frames make for slower more fragmented packets when the computers are connecting to the internet and downloading stuff? The cable/DSL modem is only 10/100 no gigabyte or jumbo frames. Will enabling jumbo frames hurt internet connections and downloads in this setup? Just as important will enabling jumbo frame support on the wireless router affect internet connection and internet downloads for wireless laptops or netbooks or smart phones or streaming media devices? Do wireless protocols support jumbo frames?

Thank you!

 

[Terry Kennedy]

BUT will enabling the jumbo frames make for slower more fragmented packets when the computers are connecting to the internet and downloading stuff? The cable/DSL modem is only 10/100 no gigabyte or jumbo frames. Will enabling jumbo frames hurt internet connections and downloads in this setup?

For TCP connections, modern implementations will use path MTU discovery to find the largest frame size supported in the end-to-end link and will only send packets of that size. Pre-MTU discovery implementations almost always assume a maximum of 1500 bytes, so you should be fine there, too.

UDP is a different matter, as there is no connection setup as part of the protocol (though applications may impose their own negotiation on top of UDP). However, a common adaptive mechanism when UDP packets don't get through is "use a smaller packet size and try again", so problems should be rare here as well.

I've been using 9K jumbos on all the devices that support it in my home network for many years now (since 2004 at least - my online config logs don't go back earlier than that).

Where you can run into trouble is if you have a local (same IP network number) path between two jumbo-capable device that isn't jumbo-clean. For example, a NAS connected to a jumbo-enabled Gigabit port on switch1, a client (also jumbo/gig) on switch2, but the connection between switch1 and switch2 is not configured for jumbo frames. In this situation, there's no router to send a "packet too big, try a smaller one" to either system, so they both think they have a jumbo-clean path but large packets are silently lost between them.

Just as important will enabling jumbo frame support on the wireless router affect internet connection and internet downloads for wireless laptops or netbooks or smart phones or streaming media devices?

You should be fine. Remember, a non-jumbo packet takes longer to transmit at 100Mbit/sec than a jumbo packet does at Gigabit speed.

Do wireless protocols support jumbo frames?

An interesting question which I've actually never considered. I'll defer to the experts here for an answer.

 

[stevech]

802.11/WiFi, cellular (TDMA, CDMA), WiMax and the rest:
An IP packet, no matter its size, is broken in to small frames and sent via one of the many wireless "MAC" and "PHY" protocols. They are received and reassembled into an IP packet.

So the size of the IP packet isn't very significant to wireless. This framing protocol doesn't happen on 802.3 (Ethernet) - one frame per packet.

HOWEVER, in any ethernet switch, router, or any other 802.3 device, support for jumbo frames is optional, per the IETF standards. The 802.3 port of a wireless device is no different.