snet: Add MTU exceeded errors

scionproto / scion

SCION Internet Architecture

https://scion.org

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snet: Add MTU exceeded errors #1328

Open scrye opened 6 years ago

scrye commented 6 years ago

snet currently does no MTU validation. This means that applications might be sending datagrams that are over the allowed length without ever being informed of this.

At the very least, snet should return an error when the MTU is exceeded.

kormat commented 6 years ago

A few comments:

currently we do not enforce the MTU, as we are still reliant on over-sized UDP packets. That said, the BRs only allow 9KiB packets, everything longer gets truncated at the moment.
this (naturally) only applies to datagram-based protocols
an additional desired feature is to be able to query snet to determine the maximum payload size for a datagram.

matzf commented 2 months ago

currently we do not enforce the MTU, as we are still reliant on over-sized UDP packets. That said, the BRs only allow 9KiB packets, everything longer gets truncated at the moment.

We still allow fragmentation, so oversize datagrams do make it through. This used to be required for the control-plane rpcs. This is no longer the case with QUIC as the transport layer for the RPCs; so this can now be fixed without breaking the control plane.