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| -rw-r--r-- | Documentation/networking/ipsec.txt | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/Documentation/networking/ipsec.txt b/Documentation/networking/ipsec.txt new file mode 100644 index 000000000000..8dbc08b7e431 --- /dev/null +++ b/Documentation/networking/ipsec.txt @@ -0,0 +1,38 @@ + +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. |