As soon as compression is disabled, traffic is being passed through the tunnels again.
Is this related to this note included with 4.14? https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/Documentation/networking/ipsec.txt?h=v4.14.6 "Here documents known IPsec corner cases which need to be keep in mind when deploy various IPsec configuration in real world production environment. 1. IPcomp: Small IP packet won't get compressed at sender, and failed on policy check on receiver. Quote from RFC3173: 2.2. Non-Expansion Policy If the total size of a compressed payload and the IPComp header, as defined in section 3, is not smaller than the size of the original payload, the IP datagram MUST be sent in the original non-compressed form. To clarify: If an IP datagram is sent non-compressed, no IPComp header is added to the datagram. This policy ensures saving the decompression processing cycles and avoiding incurring IP datagram fragmentation when the expanded datagram is larger than the MTU. Small IP datagrams are likely to expand as a result of compression. Therefore, a numeric threshold should be applied before compression, where IP datagrams of size smaller than the threshold are sent in the original form without attempting compression. The numeric threshold is implementation dependent. Current IPComp implementation is indeed by the book, while as in practice when sending non-compressed packet to the peer(whether or not packet len is smaller than the threshold or the compressed len is large than original packet len), the packet is dropped when checking the policy as this packet matches the selector but not coming from any XFRM layer, i.e., with no security path. Such naked packet will not eventually make it to upper layer. The result is much more wired to the user when ping peer with different payload length. One workaround is try to set "level use" for each policy if user observed above scenario. The consequence of doing so is small packet(uncompressed) will skip policy checking on receiver side."
Unfortunately I cannot reproduce this. When I try to ping through the tunnel with larger packets, they still won't show up in the packet counters and I do not see any outgoing packets at all. Neither compressed nor non-compressed. That tells us that the problem is on the local side though which is at least something. When pinging back from the remote site, packets are coming in and are also shown in the packet counters. However, there are no responses going out.
We have multiple units in the field testing 4.14.2 from Arne F and they are working with IPsec with compression disabled.
Timo just confirmed that this is a problem with the default Gentoo kernel. There is also a post on the strongswan mailing list about Debian. Therefore we can say that this isn't an IPFire problem. > https://lists.strongswan.org/pipermail/users/2017-December/011941.html
https://wiki.strongswan.org/issues/2478
Fixed in 4.14.12 and later. Can confirm. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=94802151894d482e82c324edf2c658f8e6b96508