Adjusting tunnel MTU

[brad]

I wanted to know if HE could add the ability to adjust the tunnels MTU through the web interface from the default of 1280 up to whatever your particular link type is capable of handling?

[eonesixfour]

What sort of link do you have?

[brad]

What sort of link do you have?

It is irrelevant what I have. To be safe the default is set lower than anything you would encounter whether it is a system co-lo'd somewhere, DSL, cable and so on. I would like to be able to adjust the MTU to match the capability of the circuit type.

[broquea]

We'll consider the suggestion.

[eonesixfour]

It is irrelevant what I have.

I fail to see how, you might have an internet2 link which has a rather large MTU, then again if you are using a HE tunnel this isn't very likely. There is a very good reason for the MTU being set to what it is, since if you have a cable connection or PPPoA you'll most likely have a MTU of 1500, PPPoE is 1492 etc, to run IPv6 over IPv4 you have a bunch of overheads and bumping the MTU will just fragment packets possibly unnecessarily etc.

[rlhdomain]

I'm getting an MTU of 1514 on my T0 interface

[brad]

an MTU of 1500 is fine all the way to 100Mbps
so unless you need jumbo frames then don't worry

The MTU of the *tunnel* is what matters, not the physical interface or virtual interface (PPPoE) providing your Internet connection. This also has nothing to do with Jumbo frames.

[brad]

I fail to see how, you might have an internet2 link which has a rather large MTU, then again if you are using a HE tunnel this isn't very likely. There is a very good reason for the MTU being set to what it is, since if you have a cable connection or PPPoA you'll most likely have a MTU of 1500, PPPoE is 1492 etc, to run IPv6 over IPv4 you have a bunch of overheads and bumping the MTU will just fragment packets possibly unnecessarily etc.

I am not talking about the MTU of my connection. I am talking about the MTU of the *tunnel*. The default and minimum MTU of the tunnel is 1280. Well below any Ethernet, cable, PPPoE, etc connection. This lower MTU will cause unnecessary fragmentation. The tunnel has an overhead of 20 bytes for the IPv4 header meaning the maximum MTU of the tunnel can be is 1480 for a connection with an MTU of 1500.

[brad]

have you even looked at the set bandwidth of the tunnel?

The bandwidth of a virtual interface (VLAN/Tunnel) is for all intents and purposes irrelevant.
Although I have used tons of Cisco gear I am not using Cisco gear at the moment for these tunnels.

the MTU only needs to be raised if the bandwidth is high and so is the quality

This is not true and even if it were true I have no issue with bandwidth or quality
of the bandwidth on my end.

on my cisco router if I type "show interface tunnel0" then I see the Bandwidth thats set and the MTU also your argument of fragmentation is invalid as a lower MTU gives less fragmentation and is more useful at lower bandwidth

Yes there is a threshold where it should be smaller than the smallest MTU of the connections between my router and HE's router but it should also be higher than the default which is currently being used.

If I was on a modem or ISDN connection then I would agree but bandwidth is not an issue.

MTU= Maximum transmition unit= Max size for per packet in bytes= 1.5 kilobytes (or more accurately 1.46KB)
and although your wan interface may be able to do 1500 without fragmentation it may not be able to do a tunnel with 1500

I never said a tunnel with an MTU of 1500. I said 1480 or in the case of a PPPoE connection 1472.

since the tunnels have differing MTU's I would assume its automaticly set by the HE point based on what can work with minimal fragmentation

The tunnels with HE do not have differing MTU's at the moment.

[snarked]

OP:  This sounds as if it's a problem with your specific configuration.  My system reports a default mtu of 1480 as expected where the real interface is 1500.  I don't see how you're getting a default of 1280.  Please explain your hardware configuration.  Something is different.

[rlhdomain]

I can't help if you can't understand

[brad]

I wanted a response from Hurricane Electric personnel involved with the Tunnel broker service, not from people who have no idea what they're talking about or random opinions.

[broquea]

FYI we are still looking into it as a configuration option inside the broker. There are just other things that require our attention at the moment.

[brad]

FYI we are still looking into it as a configuration option inside the broker. There are just other things that require our attention at the moment.

Great, thank you very much.

[eonesixfour]

OP:  This sounds as if it's a problem with your specific configuration.  My system reports a default mtu of 1480 as expected where the real interface is 1500.  I don't see how you're getting a default of 1280.  Please explain your hardware configuration.  Something is different.

I just checked mine too, and I'm seeing the MTU automatically being set at 1480 as well.