On 2018-01-05 06:59, Toshi Esumi wrote:
On 01/04/2018 07:54 AM, suse@a-domani.nl wrote:
A) it is enough to lower the MTU on the physical ethernet device on my linux box.. B) also lower the MTU of the related bridge device C) also required to lower the MTU of the other (virtual) devices connected to this bridge?
I think you got enough info already through those all replies. So I'll just add some that was missed.
1) You want to adjust mtu size at the device interface where the size is not the default size, like 1500 for copper eth (BTW you can increase it to more than 9000 for fiber GigE) for below 2) reason. PMTUD is supposed to find out the smallest MTU on the path between end to end and set the packet size below it before sending packets down to the network. However, as described at Wikipedia [https://en.wikipedia.org/wiki/Path_MTU_Discovery] IPv4 based method often doesn't work due to the fact ICMP messages are blocked by some hops/network devices between end to end. Therefore effective PMTUD needs to rely on TCP based discovery. It most unlikely works for any UDP traffic.
2) If you set MTU lower at the link interface where it's not necessary, like at your PC, all packets use that link need to be fragmented if larger than the MTU size, such as packets to your printer, network storage device, etc. You should avoid that as much as possible not to slow your LAN down. Router/FW are designed to perform it most effectively (by hardware/ASIC) than anything else. Let them do their job.
Toshi
Yes I certainly got quite some responses. And I do remember that old modems required a value of 1492 (just 8 bytes), but my max payload is 1472. Reason for asking, is thatI used a SuSE box as a firewall. One leg to cable-modem (the one with the 1472 MTU) others to internal servers, clients or wifi-modem Besides that, on the machine itself I have some virtualized machines doing common tasks like dns So all other (internal) interfaces (and bridges) I kept at the default MTU 1500 bytes, But one physical interface should be changed for certain, but I wonder if the corresponding virtual-bridge device should also lower its mtu -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org