We're using Linux kernel 4.4 for our IPsec tunnel. At one end of the tunnel, ESP packets are decrypted by kernel xfrm at a veth interface in a namespace. That veth interface also supports packet defragmentation, so fragmented packets are reassembled after decryption by kernel.

We find the kernel behavior is changed after we upgrade kernel from 4.4 to kernel 4.9 or 4.14 and the defragmentation function is removed. Because we need the defragmentation function at the veth interface, we wonder what Linux kernel code changes remove it. But we can't find anything so far because there are so many commits between these kernel versions. Does anybody know anything about this? Thank you very much in advance!

You'll probably have to bisect this yourself.

Fortunately, that's not particularly difficult or even very time consuming, if you have a semi-decent PC that can do the compiling.

That's probably the only way left. Thank you very much!