Bug 66

Summary:	pasta --config-net accepts, but does not properly handle MTUs between 65522 and 65535
Product:	passt	Reporter:	David Gibson <dgibson>
Component:	general	Assignee:	David Gibson <dgibson>
Status:	CONFIRMED ---
Severity:	normal
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	Linux
Bug Depends on:
Bug Blocks:	65

Description David Gibson 2023-07-04 05:48:18 UTC

The MTU for the guest interface in pasta defaults to 65520 bytes.  However, it can be overridden with the --mtu / -m option.  conf.c will accept any value to this option between 68 and 65535 inclusive.  However, if values of 65522 or over are given, --config-net does not complete, and the tap interface is not up and has MTU 1500 within the guest.

Comment 1 David Gibson 2023-07-04 06:05:24 UTC

This appears to be a consequence of the kernel limiting the MTU for tap devices to 65521 or less bytes.  It's another problem that would have shown up immediately if we detected and report netlink errors (see bug 60).