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how to run SKIP and natd together. Submitted by: Jim Flowers <jflowers@ezo.net> Mark this port as BROKEN until the device registration bit is fixed.
70 lines
3.5 KiB
Plaintext
70 lines
3.5 KiB
Plaintext
diff -ur --unidirectional-new-file skipsrc-1.0.orig/doc/README.FreeBSD+NAT work.new/doc/README.FreeBSD+NAT
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--- skipsrc-1.0.orig/doc/README.FreeBSD+NAT Wed Dec 31 16:00:00 1969
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+++ work.new/doc/README.FreeBSD+NAT Thu Jul 22 11:02:18 1999
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@@ -0,0 +1,65 @@
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+Using SKIP and FreeBSD's NAT (Network Address Translation) together
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+-------------------------------------------------------------------
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+
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+Skip and NAT are two very popular strategies for building secure
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+networks with FreeBSD. They are sometimes believed to be incompatable
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+when applied to the same interface. They will work together, however,
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+when correctly configured. This document addresses the reference
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+implementation of SKIP (1.0) and natd as implemented through ipfw.
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+
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+The key to understanding the operation of SKIP and NAT in parallel is to
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+realize that inbound packets traverse the ipfw ruleset twice - once as an
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+encapsulated packet and once as an de-encapsulated packet with the
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+original destination address restored. Outbound packets, on the other
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+hand, make a single pass in the unencapsulated state. This understanding
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+can be used to advantage in building a nomadic SKIP server. A nomadic SKIP
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+server allows any host equipped with a SKIP client to connect to the
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+Internet (eg. via a dialup connection to an ISP) and then establish a
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+secure connection to the nomadic SKIP server allowing full access to a
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+Local Area Network. Because the remote host may have a different IP
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+address each time it connects it is known as a nomad and its KeyID is
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+used for identification rather than the IP address identification normally
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+used to establish authenticity.
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+
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+The primary difficulty in setting up a nomadic server in conjunction with
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+NAT is not in reaching in to the LAN but in returning a response to the
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+remote host. The remote host IP address cannot, by definition, be known
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+in advance. Further - authentication of the remote host and
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+identification of its IP address by the SKIP module does not proceed to
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+update the routing tables in the kernel. A LAN host receiving a
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+connection request has insufficient information to reply to the remote
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+host either via a static route or by dynamic routing.
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+
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+This leads to the requirement that the nomadic server must be in-line
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+between the Internet and the LAN so that all packets not destined for the
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+LAN are routed to the nomadic server by the gateway address in the LAN
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+host.
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+
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+The second requirement is to prevent NAT from interfering. NAT does
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+not bother the SKIP pass as the packet header is directed to the
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+nat/skiphost. You can count the inbound SKIP packets as they
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+can be identified by the SKIP protocol (57). Use an ipfw rule
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+before the NAT rule such as:
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+
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+00010 allow skip from any to any in recv fxp0
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+00100 divert 8668 ip from any to any via fxp0
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+
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+assuming that skip is identified as 57 in /etc/protocols.
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+
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+A rule is required for the de-encrypted packets to allow them to be
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+forwarded to the LAN by the routing mechanism without interference from
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+NAT during the second pass:
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+
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+00010 allow skip from any to any in recv fxp0
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+00020 allow ip from any to 192.168.0.0/24 in recv fxp0
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+00100 divert 8668 ip from any to any via fxp0
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+
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+Now you can have nomadic hosts connect securely as part of the LAN and
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+hosts on the LAN can continue to access the Internet through NAT. Of
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+course, you have to configure the skiphost ACL correctly and setup the
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+SKIP client on the nomad to match but that's covered in the
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+documentation.
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+
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+Jim Flowers <jflowers@ezo.net>
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+#4 ISP on C|NET, #1 in Ohio
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+
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