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| author | Rene Mayrhofer <rene@mayrhofer.eu.org> | 2006-05-22 05:12:18 +0000 |
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| committer | Rene Mayrhofer <rene@mayrhofer.eu.org> | 2006-05-22 05:12:18 +0000 |
| commit | aa0f5b38aec14428b4b80e06f90ff781f8bca5f1 (patch) | |
| tree | 95f3d0c8cb0d59d88900dbbd72110d7ab6e15b2a /doc/adv_config.html | |
| parent | 7c383bc22113b23718be89fe18eeb251942d7356 (diff) | |
| download | vyos-strongswan-aa0f5b38aec14428b4b80e06f90ff781f8bca5f1.tar.gz vyos-strongswan-aa0f5b38aec14428b4b80e06f90ff781f8bca5f1.zip | |
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diff --git a/doc/adv_config.html b/doc/adv_config.html new file mode 100644 index 000000000..4b779c753 --- /dev/null +++ b/doc/adv_config.html @@ -0,0 +1,1232 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> +<HTML> +<HEAD> +<TITLE>Introduction to FreeS/WAN</TITLE> +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; CHARSET=iso-8859-1"> +<STYLE TYPE="text/css"><!-- +BODY { font-family: serif } +H1 { font-family: sans-serif } +H2 { font-family: sans-serif } +H3 { font-family: sans-serif } +H4 { font-family: sans-serif } +H5 { font-family: sans-serif } +H6 { font-family: sans-serif } +SUB { font-size: smaller } +SUP { font-size: smaller } +PRE { font-family: monospace } +--></STYLE> +</HEAD> +<BODY> +<A HREF="toc.html">Contents</A> +<A HREF="kernel.html">Previous</A> +<A HREF="install.html">Next</A> +<HR> +<H1><A name="adv_config">Other configuration possibilities</A></H1> +<P>This document describes various options for FreeS/WAN configuration + which are less used or more complex (often both) than the standard + cases described in our<A href="config.html#config"> config</A> and<A href="quickstart.html#quick_guide"> + quickstart</A> documents.</P> +<H2><A name="thumb">Some rules of thumb about configuration</A></H2> +<H3><A name="cheap.tunnel">Tunnels are cheap</A></H3> +<P>Nearly all of the overhead in IPsec processing is in the encryption + and authentication of packets. Our<A href="performance.html"> + performance</A> document discusses these overheads.</P> +<P>Beside those overheads, the cost of managing additional tunnels is + trivial. Whether your gateway supports one tunnel or ten just does not + matter. A hundred might be a problem; there is a<A href="performance.html#biggate"> + section</A> on this in the performance document.</P> +<P>So, in nearly all cases, if using multiple tunnels gives you a + reasonable way to describe what you need to do, you should describe it + that way in your configuration files.</P> +<P>For example, one user recently asked on a mailing list about this + network configuration:</P> +<PRE> netA---gwA---gwB---netB + |----netC + + netA and B are secured netC not. + netA and gwA can not access netC</PRE> +<P>The user had constructed only one tunnel, netA to netB, and wanted to + know how to use ip-route to get netC packets into it. This is entirely + unnecessary. One of the replies was:</P> +<PRE> The simplest way and indeed the right way to + solve this problem is to set up two connections: + + leftsubnet=NetA + left=gwA + right=gwB + rightsubnet=NetB + and + leftsubnet=NetA + left=gwA + right=gwB + rightsubnet=NetC</PRE> +<P>This would still be correct even if we added nets D, E, F, ... to the + above diagram and needed twenty tunnels.</P> +<P>Of course another possibility would be to just use one tunnel, with a + subnet mask that includes both netB and netC (or B, C, D, ...). See + next section.</P> +<P>In general, you can construct as many tunnels as you need. Networks + like netC in this example that do not connect directly to the gateway + are fine, as long as the gateway can route to them.</P> +<P>The number of tunnels can become an issue if it reaches 50 or so. + This is discussed in the<A href="performance.html#biggate"> performance</A> + document. Look there for information on supporting hundreds of Road + Warriors from one gateway.</P> +<P>If you find yourself with too many tunnels for some reason like + having eight subnets at one location and nine at another so you end up + with 9*8=72 tunnels, read the next section here.</P> +<H3><A name="subnet.size">Subnet sizes</A></H3> +<P>The subnets used in<VAR> leftsubnet</VAR> and<VAR> rightsubnet</VAR> + can be of any size that fits your needs, and they need not correspond + to physical networks.</P> +<P>You adjust the size by changing the<A href="glossary.html#subnet"> + subnet mask</A>, the number after the slash in the subnet description. + For example</P> +<UL> +<LI>in 192.168.100.0/24 the /24 mask says 24 bits are used to designate + the network. This leave 8 bits to label machines. This subnet has 256 + addresses. .0 and .255 are reserved, so it can have 254 machines.</LI> +<LI>A subnet with a /23 mask would be twice as large, 512 addresses.</LI> +<LI>A subnet with a /25 mask would be half the size, 128 addresses.</LI> +<LI>/0 is the whole Internet</LI> +<LI>/32 is a single machine</LI> +</UL> +<P>As an example of using these in connection descriptions, suppose your + company's head office has four physical networks using the address + ranges:</P> +<DL> +<DT>192.168.100.0/24</DT> +<DD>development</DD> +<DT>192.168.101.0/24</DT> +<DD>production</DD> +<DT>192.168.102.0/24</DT> +<DD>marketing</DD> +<DT>192.168.103.0/24</DT> +<DD>administration</DD> +</DL> +<P>You can use exactly those subnets in your connection descriptions, or + use larger subnets to grant broad access if required:</P> +<DL> +<DT>leftsubnet=192.168.100.0/24</DT> +<DD>remote hosts can access only development</DD> +<DT>leftsubnet=192.168.100.0/23</DT> +<DD>remote hosts can access development or production</DD> +<DT>leftsubnet=192.168.102.0/23</DT> +<DD>remote hosts can access marketing or administration</DD> +<DT>leftsubnet=192.168.100.0/22</DT> +<DD>remote hosts can access any of the four departments</DD> +</DL> +<P>or use smaller subnets to restrict access:</P> +<DL> +<DT>leftsubnet=192.168.103.0/24</DT> +<DD>remote hosts can access any machine in administration</DD> +<DT>leftsubnet=192.168.103.64/28</DT> +<DD>remote hosts can access only certain machines in administration.</DD> +<DT>leftsubnet=192.168.103.42/32</DT> +<DD>remote hosts can access only one particular machine in + administration</DD> +</DL> +<P>To be exact, 192.68.103.64/28 means all addresses whose top 28 bits + match 192.168.103.64. There are 16 of these because there are 16 + possibilities for the remainingg 4 bits. Their addresses are + 192.168.103.64 to 192.168.103.79.</P> +<P>Each connection description can use a different subnet if required.</P> +<P>It is possible to use all the examples above on the same FreeS/WAN + gateway, each in a different connection description, perhaps for + different classes of user or for different remote offices.</P> +<P>It is also possible to have multiple tunnels using different<VAR> + leftsubnet</VAR> descriptions with the same<VAR> right</VAR>. For + example, when the marketing manager is on the road he or she might have + access to:</P> +<DL> +<DT>leftsubnet=192.168.102.0/24</DT> +<DD>all machines in marketing</DD> +<DT>192.168.101.32/29</DT> +<DD>some machines in production</DD> +<DT>leftsubnet=192.168.103.42/32</DT> +<DD>one particular machine in administration</DD> +</DL> +<P>This takes three tunnels, but tunnels are cheap. If the laptop is set + up to build all three tunnels automatically, then he or she can access + all these machines concurrently, perhaps from different windows.</P> +<H3><A name="example.more">Other network layouts</A></H3> +<P>Here is the usual network picture for a site-to-site VPN::</P> +<PRE> Sunset==========West------------------East=========Sunrise + local net untrusted net local net</PRE> +<P>and for the Road Warrior::</P> +<PRE> telecommuter's PC or + traveller's laptop + Sunset==========West------------------East + corporate LAN untrusted net</PRE> +<P>Other configurations are also possible.</P> +<H4><A name="internet.subnet">The Internet as a big subnet</A></H4> +<P>A telecommuter might have:</P> +<PRE> Sunset==========West------------------East ================= firewall --- the Internet + home network untrusted net corporate network</PRE> +<P>This can be described as a special case of the general + subnet-to-subnet connection. The subnet on the right is 0.0.0.0/0, the + whole Internet.</P> +<P>West (the home gateway) can have its firewall rules set up so that + only IPsec packets to East are allowed out. It will then behave as if + its only connection to the world was a wire to East.</P> +<P>When machines on the home network need to reach the Internet, they do + so via the tunnel, East and the corporate firewall. From the viewpoint + of the Internet (perhaps of some EvilDoer trying to break in!), those + home office machines are behind the firewall and protected by it.</P> +<H4><A name="wireless.config">Wireless</A></H4> +<P>Another possible configuration comes up when you do not trust the + local network, either because you have very high security standards or + because your are using easily-intercepted wireless signals.</P> +<P>Some wireless networks have built-in encryption called<A href="glossary.html#WEP"> + WEP</A>, but its security is dubious. It is a fairly common practice to + use IPsec instead.</P> +<P>In this case, part of your network may look like this:</P> +<PRE> West-----------------------------East == the rest of your network + workstation untrusted wireless net</PRE> +<P>Of course, there would likely be several wireless workstations, each + with its own IPsec tunnel to the East gateway.</P> +<P>The connection descriptions look much like Road Warrior descriptions:</P> +<UL> +<LI>each workstation should have its own unique +<UL> +<LI>identifier for IPsec</LI> +<LI>RSA key</LI> +<LI>connection description.</LI> +</UL> +</LI> +<LI>on the gateway, use<VAR> left=%any</VAR>, or the workstation IP + address</LI> +<LI>on workstations,<VAR> left=%defaultroute</VAR>, or the workstation + IP address</LI> +<LI><VAR>leftsubnet=</VAR> is not used.</LI> +</UL> +<P>The<VAR> rightsubnet=</VAR> parameter might be set in any of several + ways:</P> +<DL> +<DT>rightsubnet=0.0.0.0/0</DT> +<DD>allowing workstations to access the entire Internet (see<A href="#internet.subnet"> + above</A>)</DD> +<DT>rightsubnet=a.b.c.0/24</DT> +<DD>allowing access to your entire local network</DD> +<DT>rightsubnet=a.b.c.d/32</DT> +<DD>restricting the workstation to connecting to a particular server</DD> +</DL> +<P>Of course you can mix and match these as required. For example, a + university might allow faculty full Internet access while letting + student laptops connect only to a group of lab machines.</P> +<H2><A name="choose">Choosing connection types</A></H2> +<P>One choice you need to make before configuring additional connections + is what type or types of connections you will use. There are several + options, and you can use more than one concurrently.</P> +<H3><A name="man-auto">Manual vs. automatic keying</A></H3> +<P>IPsec allows two types of connections, with manual or automatic + keying. FreeS/WAN starts them with commands such as:</P> +<PRE> ipsec manual --up <VAR>name</VAR> + ipsec auto --up <VAR>name</VAR></PRE> +<P>The difference is in how they are keyed.</P> +<DL> +<DT><A href="glossary.html#manual">Manually keyed</A> connections</DT> +<DD>use keys stored in<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf</A> +.</DD> +<DT><A href="glossary.html#auto">Automatically keyed</A> connections</DT> +<DD>use keys automatically generated by the Pluto key negotiation + daemon. The key negotiation protocol,<A href="glossary.html#IKE"> IKE</A> +, must authenticate the other system. (It is vulnerable to a<A href="glossary.html#middle"> + man-in-the-middle attack</A> if used without authentication.) We + currently support two authentication methods: +<UL> +<LI>using shared secrets stored in<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets</A>.</LI> +<LI>RSA<A href="glossary.html#public"> public key</A> authentication, + with our machine's private key in<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets</A>. Public keys for other machines may either be placed + in<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf</A> or provided via + DNS.</LI> +</UL> +<P>A third method, using RSA keys embedded in<A href="glossary.html#X509"> + X.509</A> certtificates, is provided by user<A href="web.html#patch"> + patches</A>.</P> +</DD> +</DL> +<P><A href="glossary.html#manual">Manually keyed</A> connections provide + weaker security than<A href="glossary.html#auto"> automatically keyed</A> + connections. An opponent who reads ipsec.secrets(5) gets your + encryption key and can read all data encrypted by it. If he or she has + an archive of old messages, all of them back to your last key change + are also readable.</P> +<P>With automatically-(re)-keyed connections, an opponent who reads + ipsec.secrets(5) gets the key used to authenticate your system in IKE + -- the shared secret or your private key, depending what authentication + mechanism is in use. However, he or she does not automatically gain + access to any encryption keys or any data.</P> +<P>An attacker who has your authentication key can mount a<A href="glossary.html#middle"> + man-in-the-middle attack</A> and, if that succeeds, he or she will get + encryption keys and data. This is a serious danger, but it is better + than having the attacker read everyting as soon as he or she breaks + into ipsec.secrets(5).. Moreover, the keys change often so an opponent + who gets one key does not get a large amount of data. To read all your + data, he or she would have to do a man-in-the-middle attack at every + key change.</P> +<P>We discuss using<A href="#prodman"> manual keying in production</A> + below, but this is<STRONG> not recommended</STRONG> except in special + circumstances, such as needing to communicate with some implementation + that offers no auto-keyed mode compatible with FreeS/WAN.</P> +<P>Manual keying may also be useful for testing. There is some + discussion of this in our<A href="faq.html#man4debug"> FAQ</A>.</P> +<H3><A name="auto-auth">Authentication methods for auto-keying</A></H3> +<P>The IKE protocol which Pluto uses to negotiate connections between + gateways must use some form of authentication of peers. A gateway must + know who it is talking to before it can create a secure connection. We + support two basic methods for this authentication:</P> +<UL> +<LI>shared secrets, stored in<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets(5)</A></LI> +<LI>RSA authentication</LI> +</UL> +<P>There are, howver, several variations on the RSA theme, using + different methods of managing the RSA keys:</P> +<UL> +<LI>our RSA private key in<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets(5)</A> with other gateways' public keys +<DL> +<DT>either</DT> +<DD>stored in<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf(5)</A></DD> +<DT>or</DT> +<DD>looked up via<A href="glossary.html#DNS"> DNS</A></DD> +</DL> +</LI> +<LI>authentication with<A href="glossary.html#x509"> x.509</A> + certificates.; See our<A href="web.html#patch"> links section</A> for + information on user-contributed patches for this.:</LI> +</UL> +<P>Public keys in<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf(5</A> +) give a reasonably straightforward method of specifying keys for + explicitly configured connections.</P> +<P>Putting public keys in DNS allows us to support<A href="glossary.html#carpediem"> + opportunistic encryption</A>. Any two FreeS/WAN gateways can provide + secure communication, without either of them having any preset + information about the other.</P> +<P>X.509 certificates may be required to interface to various<A href="glossary.html#PKI"> + PKI</A>s.</P> +<H3><A name="adv-pk">Advantages of public key methods</A></H3> +<P>Authentication with a<A href="glossary.html#public"> public key</A> + method such as<A href="glossary.html#RSA"> RSA</A> has some important + advantages over using shared secrets.</P> +<UL> +<LI>no problem of secure transmission of secrets +<UL> +<LI>A shared secret must be shared, so you have the problem of + transmitting it securely to the other party. If you get this wrong, you + have no security.</LI> +<LI>With a public key technique, you transmit only your public key. The + system is designed to ensure that it does not matter if an enemy + obtains public keys. The private key never leaves your machine.</LI> +</UL> +</LI> +<LI>easier management +<UL> +<LI>Suppose you have 20 branch offices all connecting to one gateway at + head office, and all using shared secrets. Then the head office admin + has 20 secrets to manage. Each of them must be kept secret not only + from outsiders, but also from 19 of the branch office admins. The + branch office admins have only one secret each to manage. +<P>If the branch offices need to talk to each other, this becomes + problematic. You need another 20*19/2 = 190 secrets for + branch-to-branch communication, each known to exactly two branches. Now + all the branch admins have the headache of handling 20 keys, each + shared with exactly one other branch or with head office.</P> +<P>For larger numbers of branches, the number of connections and secrets + increases quadratically and managing them becomes a nightmare. A + 1000-gateway fully connected network needs 499,500 secrets, each known + to exactly two players. There are ways to reduce this problem, for + example by introducing a central key server, but these involve + additional communication overheads, more administrative work, and new + threats that must be carefully guarded against.</P> +</LI> +<LI>With public key techniques, the<EM> only</EM> thing you have to keep + secret is your private key, and<EM> you keep that secret from everyone</EM> +. +<P>As network size increaes, the number of public keys used increases + linearly with the number of nodes. This still requires careful + administration in large applications, but is nothing like the disaster + of a quadratic increase. On a 1000-gateway network, you have 1000 + private keys, each of which must be kept secure on one machine, and + 1000 public keys which must be distributed. This is not a trivial + problem, but it is manageable.</P> +</LI> +</UL> +</LI> +<LI>does not require fixed IP addresses +<UL> +<LI>When shared secrets are used in IPsec, the responder must be able to + tell which secret to use by looking at the IP address on the incoming + packets. When the other parties do not have a fixed IP address to be + identified by (for example, on nearly all dialup ISP connections and + many cable or ADSL links), this does not work well -- all must share + the same secret!</LI> +<LI>When RSA authentication is in use, the initiator can identify itself + by name before the key must be determined. The responder then checks + that the message is signed with the public key corresponding to that + name.</LI> +</UL> +</LI> +</UL> +<P>There is also a disadvantage:</P> +<UL> +<LI>your private key is a single point of attack, extremely valuable to + an enemy +<UL> +<LI>with shared secrets, an attacker who steals your ipsec.secrets file + can impersonate you or try<A href="glossary.html#middle"> + man-in-the-middle</A> attacks, but can only attack connections + described in that file</LI> +<LI>an attacker who steals your private key gains the chance to attack + not only existing connections<EM> but also any future connections</EM> + created using that key</LI> +</UL> +</LI> +</UL> +<P>This is partly counterbalanced by the fact that the key is never + transmitted and remains under your control at all times. It is likely + necessary, however, to take account of this in setting security policy. + For example, you should change gateway keys when an administrator + leaves the company, and should change them periodically in any case.</P> +<P>Overall, public key methods are<STRONG> more secure, more easily + managed and more flexible</STRONG>. We recommend that they be used for + all connections, unless there is a compelling reason to do otherwise.</P> +<H2><A name="prodsecrets">Using shared secrets in production</A></H2> +<P>Generally, public key methods are preferred for reasons given above, + but shared secrets can be used with no loss of security, just more work + and perhaps more need to take precautions.</P> +<P>What I call "shared secrets" are sometimes also called "pre-shared + keys". They are used only for for authentication, never for encryption. + Calling them "pre-shared keys" has confused some users into thinking + they were encryption keys, so I prefer to avoid the term..</P> +<P>If you are interoperating with another IPsec implementation, you may + find its documentation calling them "passphrases".</P> +<H3><A name="secrets">Putting secrets in ipsec.secrets(5)</A></H3> +<P>If shared secrets are to be used to<A href="glossary.html#authentication"> + authenticate</A> communication for the<A href="glossary.html#DH"> + Diffie-Hellman</A> key exchange in the<A href="glossary.html#IKE"> IKE</A> + protocol, then those secrets must be stored in<VAR> /etc/ipsec.secrets</VAR> +. For details, see the<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets(5)</A> man page.</P> +<P>A few considerations are vital:</P> +<UL> +<LI>make the secrets long and unguessable. Since they need not be + remembered by humans, very long ugly strings may be used. We suggest + using our<A href="manpage.d/ipsec_ranbits.8.html"> ipsec_ranbits(8)</A> + utility to generate long (128 bits or more) random strings.</LI> +<LI>transmit secrets securely. You have to share them with other + systems, but you lose if they are intercepted and used against you. Use<A +href="glossary.html#PGP"> PGP</A>,<A href="glossary.html#SSH"> SSH</A>, + hand delivery of a floppy disk which is then destroyed, or some other + trustworthy method to deliver them.</LI> +<LI>store secrets securely, in root-owned files with permissions + rw------.</LI> +<LI>limit sharing of secrets. Alice, Bob, Carol and Dave may all talk to + each other, but only Alice and Bob should know the secret for an + Alice-Bob link.</LI> +<LI><STRONG>do not share private keys</STRONG>. The private key for RSA + authentication of your system is stored in<A href="manpage.d/ipsec.secrets.5.html"> + ipsec.secrets(5)</A>, but it is a different class of secret from the + pre-shared keys used for the "shared secret" authentication. No-one but + you should have the RSA private key.</LI> +</UL> +<P>Each line has the IP addresses of the two gateways plus the secret. + It should look something like this:</P> +<PRE> 10.0.0.1 11.0.0.1 : PSK "jxTR1lnmSjuj33n4W51uW3kTR55luUmSmnlRUuWnkjRj3UuTV4T3USSu23Uk55nWu5TkTUnjT"</PRE> +<P><VAR>PSK</VAR> indicates the use of a<STRONG> p</STRONG>re-<STRONG>s</STRONG> +hared<STRONG> k</STRONG>ey. The quotes and the whitespace shown are + required.</P> +<P>You can use any character string as your secret. For security, it + should be both long and extremely hard to guess. We provide a utility + to generate such strings,<A href="manpage.d/ipsec_ranbits.8.html"> + ipsec_ranbits(8)</A>.</P> +<P>You want the same secret on the two gateways used, so you create a + line with that secret and the two gateway IP addresses. The + installation process supplies an example secret, useful<EM> only</EM> + for testing. You must change it for production use.</P> +<H3><A name="securing.secrets">File security</A></H3> +<P>You must deliver this file, or the relevant part of it, to the other + gateway machine by some<STRONG> secure</STRONG> means.<EM> Don't just + FTP or mail the file!</EM> It is vital that the secrets in it remain + secret. An attacker who knew those could easily have<EM> all the data + on your "secure" connection</EM>.</P> +<P>This file must be owned by root and should have permissions<VAR> + rw-------</VAR>.</P> +<H3><A name="notroadshared">Shared secrets for road warriors</A></H3> +<P>You can use a shared secret to support a single road warrior + connecting to your gateway, and this is a reasonable thing to do in + some circumstances. Public key methods have advantages, discussed<A href="#choose"> + above</A>, but they are not critical in this case.</P> +<P>To do this, the line in ipsec.secrets(5) is something like:</P> +<PRE> 10.0.0.1 0.0.0.0 : PSK "jxTR1lnmSjuj33n4W51uW3kTR55luUmSmnlRUuWnkjRj3UuTV4T3USSu23Uk55nWu5TkTUnjT"</PRE> + where the<VAR> 0.0.0.0</VAR> means that any IP address is acceptable. +<P><STRONG>For more than one road warrior, shared secrets are<EM> not</EM> + recommended.</STRONG> If shared secrets are used, then when the + responder needs to look up the secret, all it knows about the sender is + an IP address. This is fine if the sender is at a fixed IP address + specified in the config file. It is also fine if only one road warrior + uses the wildcard<VAR> 0.0.0.0</VAR> address. However, if you have more + than one road warrior using shared secret authentication, then they + must all use that wildcard and therefore<STRONG> all road warriors + using PSK autentication must use the same secret</STRONG>. Obviously, + this is insecure.</P> +<P><STRONG>For multiple road warriors, use public key authentication.</STRONG> + Each roadwarrior can then have its own identity (our<VAR> leftid=</VAR> + or<VAR> rightid=</VAR> parameters), its own public/private key pair, + and its own secure connection.</P> +<H2><A name="prodman">Using manual keying in production</A></H2> +<P>Generally,<A href="glossary.html#auto"> automatic keying</A> is + preferred over<A href="glossary.html#manual"> manual keying</A> for + production use because it is both easier to manage and more secure. + Automatic keying frees the admin from much of the burden of managing + keys securely, and can provide<A href="glossary.html#PFS"> perfect + forward secrecy</A>. This is discussed in more detail<A href="#man-auto"> + above</A>.</P> +<P>However, it is possible to use manual keying in production if that is + what you want to do. This might be necessary, for example, in order to + interoperate with some device that either does not provide automatic + keying or provides it in some version we cannot talk to.</P> +<P>Note that with manual keying<STRONG> all security rests with the keys</STRONG> +. If an adversary acquires your keys, you've had it. He or she can read + everything ever sent with those keys, including old messages he or she + may have archived.</P> +<P>You need to<STRONG> be really paranoid about keys</STRONG> if you're + going to rely on manual keying for anything important.</P> +<UL> +<LI>keep keys in files with 600 permissions, owned by root</LI> +<LI>be extremely careful about security of your gateway systems. Anyone + who breaks into a gateway and gains root privileges can get all your + keys and read everything ever encrypted with those keys, both old + messages he has archived and any new ones you may send.</LI> +<LI>change keys regularly. This can be a considerable bother, (and + provides an excellent reason to consider automatic keying instead), but + it is<EM> absolutely essential</EM> for security. Consider a manually + keyed system in which you leave the same key in place for months: +<UL> +<LI>an attacker can have a very large sample of text sent with that key + to work with. This makes various cryptographic attacks much more likely + to succeed.</LI> +<LI>The chances of the key being compromised in some non-cryptographic + manner -- a spy finds it on a discarded notepad, someone breaks into + your server or your building and steals it, a staff member is bribed, + tricked, seduced or coerced into revealing it, etc. -- also increase + over time.</LI> +<LI>a successful attacker can read everything ever sent with that key. + This makes any successful attack extremely damaging.</LI> +</UL> + It is clear that you must change keys often to have any useful + security. The only question is how often.</LI> +<LI>use<A href="glossary.html#PGP"> PGP</A> or<A href="glossary.html#SSH"> + SSH</A> for all key transfers</LI> +<LI>don't edit files with keys in them when someone can look over your + shoulder</LI> +<LI>worry about network security; could someone get keys by snooping + packets on the LAN between your X desktop and the gateway?</LI> +<LI>lock up your backup tapes for the gateway system</LI> +<LI>... and so on</LI> +</UL> +<P>Linux FreeS/WAN provides some facilities to help with this. In + particular, it is good policy to<STRONG> keep keys in separate files</STRONG> + so you can edit configuration information in /etc/ipsec.conf without + exposing keys to "shoulder surfers" or network snoops. We support this + with the<VAR> also=</VAR> and<VAR> include</VAR> syntax in<A href="manpage.d/ipsec.conf.5.html"> + ipsec.conf(5)</A>.</P> +<P>See the last example in our<A href="examples"> examples</A> file. In + the /etc/ipsec.conf<VAR> conn samplesep</VAR> section, it has the line:</P> +<PRE> also=samplesep-keys</PRE> +<P>which tells the "ipsec manual" script to insert the configuration + description labelled "samplesep-keys" if it can find it. The + /etc/ipsec.conf file must also have a line such as:</P> +<PRE>include ipsec.*.conf</PRE> +<P>which tells it to read other files. One of those other files then + might contain the additional data:</P> +<PRE>conn samplesep-keys + spi=0x200 + esp=3des-md5-96 + espenckey=0x01234567_89abcdef_02468ace_13579bdf_12345678_9abcdef0 + espauthkey=0x12345678_9abcdef0_2468ace0_13579bdf</PRE> +<P>The first line matches the label in the "also=" line, so the indented + lines are inserted. The net effect is exactly as if the inserted lines + had occurred in the original file in place of the "also=" line.</P> +<P>Variables set here are:</P> +<DL> +<DT>spi</DT> +<DD>A number needed by the manual keying code. Any 3-digit hex number + will do, but if you have more than one manual connection then<STRONG> + spi must be different</STRONG> for each connection.</DD> +<DT>esp</DT> +<DD>Options for<A href="glossary.html#ESP"> ESP</A> (Encapsulated + Security Payload), the usual IPsec encryption mode. Settings here are + for<A href="glossary.html#encryption"> encryption</A> using<A href="glossary.html#3DES"> + triple DES</A> and<A href="glossary.html#authentication"> + authentication</A> using<A href="glossary.html#MD5"> MD5</A>. Note that + encryption without authentication should not be used; it is insecure.</DD> +<DT>espenkey</DT> +<DD>Key for ESP encryption. Here, a 192-bit hex number for triple DES.</DD> +<DT>espauthkey</DT> +<DD>Key for ESP authentication. Here, a 128-bit hex number for MD5.</DD> +</DL> +<P><STRONG>Note</STRONG> that the<STRONG> example keys we supply</STRONG> + are intended<STRONG> only for testing</STRONG>. For real use, you + should go to automatic keying. If that is not possible, create your own + keys for manual mode and keep them secret</P> +<P>Of course, any files containing keys<STRONG> must</STRONG> have 600 + permissions and be owned by root.</P> +<P>If you connect in this way to multiple sites, we recommend that you + keep keys for each site in a separate file and adopt some naming + convention that lets you pick them all up with a single "include" line. + This minimizes the risk of losing several keys to one error or attack + and of accidentally giving another site admin keys which he or she has + no business knowing.</P> +<P>Also note that if you have multiple manually keyed connections on a + single machine, then the<VAR> spi</VAR> parameter must be different for + each one. Any 3-digit hex number is OK, provided they are different for + each connection. We reserve the range 0x100 to 0xfff for manual + connections. Pluto assigns SPIs from 0x1000 up for automatically keyed + connections.</P> +<P>If<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf(5)</A> contains + keys for manual mode connections, then it too must have permissions<VAR> + rw-------</VAR>. We recommend instead that, if you must manual keying + in production, you keep the keys in separate files.</P> +<P>Note also that<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf</A> + is installed with permissions<VAR> rw-r--r--</VAR>. If you plan to use + manually keyed connections for anything more than initial testing, you<B> + must</B>:</P> +<UL> +<LI>either change permissions to<VAR> rw-------</VAR></LI> +<LI>or store keys separately in secure files and access them via include + statements in<A href="manpage.d/ipsec.conf.5.html"> ipsec.conf</A>.</LI> +</UL> +<P>We recommend the latter method for all but the simplest + configurations.</P> +<H3><A name="ranbits">Creating keys with ranbits</A></H3> +<P>You can create new<A href="glossary.html#random"> random</A> keys + with the<A href="manpage.d/ipsec_ranbits.8.html"> ranbits(8)</A> + utility. For example, the commands:</P> +<PRE> umask 177 + ipsec ranbits 192 > temp + ipsec ranbits 128 >> temp</PRE> +<P>create keys in the sizes needed for our default algorithms:</P> +<UL> +<LI>192-bit key for<A href="glossary.html#3DES"> 3DES</A> encryption +<BR> (only 168 bits are used; parity bits are ignored)</LI> +<LI>128-bit key for keyed<A href="glossary.html#MD5"> MD5</A> + authentication</LI> +</UL> +<P>If you want to use<A href="glossary.html#SHA"> SHA</A> instead of<A href="glossary.html#MD5"> + MD5</A>, that requires a 160-bit key</P> +<P>Note that any<STRONG> temporary files</STRONG> used must be kept<STRONG> + secure</STRONG> since they contain keys. That is the reason for the + umask command above. The temporary file should be deleted as soon as + you are done with it. You may also want to change the umask back to its + default value after you are finished working on keys.</P> +<P>The ranbits utility may pause for a few seconds if not enough entropy + is available immediately. See ipsec_ranbits(8) and random(4) for + details. You may wish to provide some activity to feed entropy into the + system. For example, you might move the mouse around, type random + characters, or do<VAR> du /usr > /dev/null</VAR> in the background.</P> +<H2><A name="boot">Setting up connections at boot time</A></H2> +<P>You can tell the system to set up connections automatically at boot + time by putting suitable stuff in /etc/ipsec.conf on both systems. The + relevant section of the file is labelled by a line reading<VAR> config + setup</VAR>.</P> +<P>Details can be found in the<A href="manpage.d/ipsec.conf.5.html"> + ipsec.conf(5)</A> man page. We also provide a file of<A href="examples"> + example configurations</A>.</P> +<P>The most likely options are something like:</P> +<DL> +<DT>interfaces="ipsec0=eth0 ipsec1=ppp0"</DT> +<DD>Tells KLIPS which interfaces to use. Up to four interfaces numbered + ipsec[0-3] are supported. Each interface can support an arbitrary + number of tunnels. +<P>Note that for PPP, you give the ppp[0-9] device name here, not the + underlying device such as modem (or eth1 if you are using PPPoE).</P> +</DD> +<DT>interfaces=%defaultroute</DT> +<DD>Alternative setting, useful in simple cases. KLIPS will pick up both + its interface and the next hop information from the settings of the + Linux default route.</DD> +<DT>forwardcontrol=no</DT> +<DD>Normally "no". Set to "yes" if the IP forwarding option is disabled + in your network configuration. (This can be set as a kernel + configuration option or later. e.g. on Redhat, it's in + /etc/sysconfig/network and on SuSE you can adjust it with Yast.) Linux + FreeS/WAN will then enable forwarding when starting up and turn it off + when going down. This is used to ensure that no packets will be + forwarded before IPsec comes up and takes control.</DD> +<DT>syslog=daemon.error</DT> +<DD>Used in messages to the system logging daemon (syslogd) to specify + what type of software is sending the messages. If the settings are + "daemon.error" as in our example, then syslogd treats the messages as + error messages from a daemon. +<P>Note that<A href="glossary.html#Pluto"> Pluto</A> does not currently + pay attention to this variable. The variable controls setup messages + only.</P> +</DD> +<DT>klipsdebug=</DT> +<DD>Debug settings for<A href="glossary.html#KLIPS"> KLIPS</A>.</DD> +<DT>plutodebug=</DT> +<DD>Debug settings for<A href="glossary.html#Pluto"> Pluto</A>.</DD> +<DT>... for both the above DEBUG settings</DT> +<DD>Normally, leave empty as shown above for no debugging output. +<BR> Use "all" for maximum information. +<BR> See ipsec_klipsdebug(8) and ipsec_pluto(8) man page for other + options. Beware that if you set /etc/ipsec.conf to enable debug output, + your system's log files may get large quickly.</DD> +<DT>dumpdir=/safe/directory</DT> +<DD>Normally, programs started by ipsec setup don't crash. If they do, + by default, no core dump will be produced because such dumps would + contain secrets. If you find you need to debug such crashes, you can + set dumpdir to the name of a directory in which to collect the core + file.</DD> +<DT>manualstart=</DT> +<DD>List of manually keyed connections to be automatically started at + boot time. Useful for testing, but not for long term use. Connections + which are automatically started should also be automatically re-keyed.</DD> +<DT>pluto=yes</DT> +<DD>Whether to start<A href="glossary.html#Pluto"> Pluto</A> when ipsec + startup is done. +<BR> This parameter is optional and defaults to "yes" if not present. +<P>"yes" is strongly recommended for production use so that the keying + daemon (Pluto) will automatically re-key the connections regularly. The + ipsec-auto parameters ikelifetime, ipseclifetime and reykeywindow give + you control over frequency of rekeying.</P> +</DD> +<DT>plutoload="reno-van reno-adam reno-nyc"</DT> +<DD>List of tunnels (by name, e.g. fred-susan or reno-van in our + examples) to be loaded into Pluto's internal database at startup. In + this example, Pluto loads three tunnels into its database when it is + started. +<P>If plutoload is "%search", Pluto will load any connections whose + description includes "auto=add" or "auto=start".</P> +</DD> +<DT>plutostart="reno-van reno-adam reno-nyc"</DT> +<DD>List of tunnels to attempt to negotiate when Pluto is started. +<P>If plutostart is "%search", Pluto will start any connections whose + description includes "auto=start".</P> +<P>Note that, for a connection intended to be permanent,<STRONG> both + gateways should be set try to start</STRONG> the tunnel. This allows + quick recovery if either gateway is rebooted or has its IPsec + restarted. If only one gateway is set to start the tunnel and the other + gateway restarts, the tunnel may not be rebuilt.</P> +</DD> +<DT>plutowait=no</DT> +<DD>Controls whether Pluto waits for one tunnel to be established before + starting to negotiate the next. You might set this to "yes" +<UL> +<LI>if your gateway is a very limited machine and you need to conserve + resources.</LI> +<LI>for debugging; the logs are clearer if only one connection is + brought up at a time</LI> +</UL> + For a busy and resource-laden production gateway, you likely want "no" + so that connections are brought up in parallel and the whole process + takes less time.</DD> +</DL> +<P>The example assumes you are at the Reno office and will use IPsec to + Vancouver, New York City and Amsterdam.</P> +<H2><A name="multitunnel">Multiple tunnels between the same two gateways</A> +</H2> +<P>Consider a pair of subnets, each with a security gateway, connected + via the Internet:</P> +<PRE> 192.168.100.0/24 left subnet + | + 192.168.100.1 + North Gateway + 101.101.101.101 left + | + 101.101.101.1 left next hop + [Internet] + 202.202.202.1 right next hop + | + 202.202.202.202 right + South gateway + 192.168.200.1 + | + 192.168.200.0/24 right subnet</PRE> +<P>A tunnel specification such as:</P> +<PRE>conn northnet-southnet + left=101.101.101.101 + leftnexthop=101.101.101.1 + leftsubnet=192.168.100.0/24 + leftfirewall=yes + right=202.202.202.202 + rightnexthop=202.202.202.1 + rightsubnet=192.168.200.0/24 + rightfirewall=yes</PRE> + will allow machines on the two subnets to talk to each other. You might + test this by pinging from polarbear (192.168.100.7) to penguin + (192.168.200.5). +<P>However,<STRONG> this does not cover other traffic you might want to + secure</STRONG>. To handle all the possibilities, you might also want + these connection descriptions:</P> +<PRE>conn northgate-southnet + left=101.101.101.101 + leftnexthop=101.101.101.1 + right=202.202.202.202 + rightnexthop=202.202.202.1 + rightsubnet=192.168.200.0/24 + rightfirewall=yes + +conn northnet-southgate + left=101.101.101.101 + leftnexthop=101.101.101.1 + leftsubnet=192.168.100.0/24 + leftfirewall=yes + right=202.202.202.202 + rightnexthop=202.202.202.1</PRE> +<P>Without these, neither gateway can do IPsec to the remote subnet. + There is no IPsec tunnel or eroute set up for the traffic.</P> +<P>In our example, with the non-routable 192.168.* addresses used, + packets would simply be discarded. In a different configuration, with + routable addresses for the remote subnet,<STRONG> they would be sent + unencrypted</STRONG> since there would be no IPsec eroute and there + would be a normal IP route.</P> +<P>You might also want:</P> +<PRE>conn northgate-southgate + left=101.101.101.101 + leftnexthop=101.101.101.1 + right=202.202.202.202 + rightnexthop=202.202.202.1</PRE> +<P>This is required if you want the two gateways to speak IPsec to each + other.</P> +<P>This requires a lot of duplication of details. Judicious use of<VAR> + also=</VAR> and<VAR> include</VAR> can reduce this problem.</P> +<P>Note that, while FreeS/WAN supports all four tunnel types, not all + implementations do. In particular, some versions of Windows 2000 and + the freely downloadable version of PGP provide only "client" + functionality. You cannot use them as gateways with a subnet behind + them. To get that functionality, you must upgrade to Windows 2000 + server or the commercially available PGP products.</P> +<H3><A name="advroute">One tunnel plus advanced routing</A></H3> + It is also possible to use the new routing features in 2.2 and later + kernels to avoid most needs for multple tunnels. Here is one mailing + list message on the topic: +<PRE>Subject: Re: linux-ipsec: IPSec packets not entering tunnel? + Date: Mon, 20 Nov 2000 + From: Justin Guyett <jfg@sonicity.com> + +On Mon, 20 Nov 2000, Claudia Schmeing wrote: + +> Right Left +> "home" "office" +> 10.92.10.0/24 ---- 24.93.85.110 ========= 216.175.164.91 ---- 10.91.10.24/24 +> +> I've created all four tunnels, and can ping to test each of them, +> *except* homegate-officenet. + +I keep wondering why people create all four tunnels. Why not route +traffic generated from home to 10.91.10.24/24 out ipsec0 with iproute2? +And 99% of the time you don't need to access "office" directly, which +means you can eliminate all but the subnet<->subnet connection.</PRE> + and FreeS/WAN technical lead Henry Spencer's comment: +<PRE>> I keep wondering why people create all four tunnels. Why not route +> traffic generated from home to 10.91.10.24/24 out ipsec0 with iproute2? + +This is feasible, given some iproute2 attention to source addresses, but +it isn't something we've documented yet... (partly because we're still +making some attempt to support 2.0.xx kernels, which can't do this, but +mostly because we haven't caught up with it yet). + +> And 99% of the time you don't need to access "office" directly, which +> means you can eliminate all but the subnet<->subnet connection. + +Correct in principle, but people will keep trying to ping to or from the +gateways during testing, and sometimes they want to run services on the +gateway machines too.</PRE> + +<!-- Is this in the right spot in this document? --> +<H2><A name="opp.gate">An Opportunistic Gateway</A></H2> +<H3><A NAME="14_7_1">Start from full opportunism</A></H3> +<P>Full opportunism allows you to initiate and receive opportunistic + connections on your machine. The remaining instructions in this section + assume you have first set up full opportunism on your gateway using<A HREF="quickstart.html#opp.incoming"> + these instructions</A>. Both sets of instructions require mailing DNS + records to your ISP. Collect DNS records for both the gateway (above) + and the subnet nodes (below) before contacting your ISP.</P> +<H3><A NAME="14_7_2">Reverse DNS TXT records for each protected machine</A> +</H3> +<P>You need these so that your Opportunistic peers can:</P> +<UL> +<LI>discover the gateway's address, knowing only the IP address that + packets are bound for</LI> +<LI>verify that the gateway is authorised to encrypt for that endpoint</LI> +</UL> +<P>On the gateway, generate a TXT record with:</P> +<PRE> ipsec showhostkey --txt 192.0.2.11</PRE> +<P>Use your gateway address in place of 192.0.2.11.</P> +<P>You should see (keys are trimmed for clarity throughout our example):</P> +<PRE> ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"</PRE> +<P><B>This MUST BE the same key as in your gateway's TXT record, or + nothing will work.</B></P> +<P>In a text file, make one copy of this TXT record for each subnet + node:</P> +<PRE> ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/" + + ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/" + + ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"</PRE> +<P>Above each entry, insert a line like this:</P> +<PRE> 98.2.0.192.in-addr.arpa. IN PTR arthur.example.com.</PRE> +<P>It must include:</P> +<UL> +<LI>The subnet node's address in reverse map format. For example, + 192.0.2.120 becomes<VAR> 120.2.0.192.in-addr.arpa.</VAR>. Note the + final period.</LI> +<LI><VAR>IN PTR</VAR></LI> +<LI>The node's name, ie.<VAR> arthur.example.com.</VAR>. Note the final + period.</LI> +</UL> +<P>The result will be a file of TXT records, like this:</P> +<PRE> 98.2.0.192.in-addr.arpa. IN PTR arthur.example.com. + ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/" + + 99.2.0.192.in-addr.arpa. IN PTR ford.example.com. + ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/" + + 100.2.0.192.in-addr.arpa. IN PTR trillian.example.com. + ; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 + IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"</PRE> +<H3><A NAME="14_7_3">Publish your records</A></H3> +<P>Ask your ISP to publish all the reverse DNS records you have + collected. There may be a delay of up to 48 hours as the records + propagate.</P> +<H3><A NAME="14_7_4">...and test them</A></H3> +<P>Check a couple of records with commands like this one:</P> +<PRE> ipsec verify --host ford.example.com + ipsec verify --host trillian.example.com</PRE> +<P>The<VAR> verify</VAR> command checks for TXT records for both the + subnet host and its gateway. You should see output like:</P> +<PRE> ... + Looking for TXT in reverse map: 99.2.0.192.in-addr.arpa [OK] + ... + Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK] + ... + Looking for TXT in reverse map: 100.2.0.192.in-addr.arpa [OK] + ... + Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK] + ...</PRE> +<H3><A NAME="14_7_5">No Configuration Needed</A></H3> +<P>FreeS/WAN 2.x ships with a built-in, automatically enabled OE + connection<VAR> conn packetdefault</VAR> which applies OE, if possible, + to all outbound traffic routed through the FreeS/WAN box. The<A HREF="manpage.d/ipsec.conf.5.html"> + ipsec.conf(5) manual</A> describes this connection in detail. While the + effect is much the same as<VAR> private-or-clear</VAR>, the + implementation is different: notably, it does not use policy groups.</P> +<P>You can create more complex OE configurations for traffic forwarded + through a FreeS/WAN box, as explained in our<A HREF="policygroups.html#policygroups"> + policy groups document</A>, or disable OE using<A HREF="policygroups.html#disable_policygroups"> + these instructions</A>.</P> +<H2><A name="extruded.config">Extruded Subnets</A></H2> +<P>What we call<A href="glossary.html#extruded"> extruded subnets</A> + are a special case of<A href="glossary.html#VPN.gloss"> VPNs</A>.</P> +<P>If your buddy has some unused IP addresses, in his subnet far off at + the other side of the Internet, he can loan them to you... provided + that the connection between you and him is fast enough to carry all the + traffic between your machines and the rest of the Internet. In effect, + he "extrudes" a part of his address space over the network to you, with + your Internet traffic appearing to originate from behind his Internet + gateway.</P> +<P>As far as the Internet is concerned, your new extruded net is behind + your buddy's gateway. You route all your packets for the Internet at + large out his gateway, and receive return packets the same way. You + route your local packets locally.</P> +<P>Suppose your friend has a.b.c.0/24 and wants to give you + a.b.c.240/28. The initial situation is:</P> +<PRE> subnet gateway Internet + a.b.c.0/24 a.b.c.1 p.q.r.s</PRE> + where anything from the Internet destined for any machine in a.b.c.0/24 + is routed via p.q.r.s and that gateway knows what to do from there. +<P>Of course it is quite normal for various smaller subnets to exist + behind your friend's gateway. For example, your friend's company might + have a.b.c.16/28=development, a.b.c.32/28=marketing and so on. The + Internet neither knows not cares about this; it just delivers packets + to the p.q.r.s and lets the gateway do whatever needs to be done from + there.</P> +<P>What we want to do is take a subnet, perhaps a.b.c.240/28, out of + your friend's physical location<EM> while still having your friend's + gateway route to it</EM>. As far as the Internet is concerned, you + remain behind that gateway.</P> +<PRE> subnet gateway Internet your gate extruded + + a.b.c.0/24 a.b.c.1 p.q.r.s d.e.f.g a.b.c.240/28 + + ========== tunnel ==========</PRE> +<P>The extruded addresses have to be a complete subnet.</P> +<P>In our example, the friend's security gateway is also his Internet + gateway, but this is not necessary. As long as all traffic from the + Internet to his addresses passes through the Internet gate, the + security gate could be a machine behind that. The IG would need to + route all traffic for the extruded subnet to the SG, and the SG could + handle the rest.</P> +<P>First, configure your subnet using the extruded addresses. Your + security gateway's interface to your subnet needs to have an extruded + address (possibly using a Linux<A href="glossary.html#virtual"> virtual + interface</A>, if it also has to have a different address). Your + gateway needs to have a route to the extruded subnet, pointing to that + interface. The other machines at your site need to have addresses in + that subnet, and default routes pointing to your gateway.</P> +<P>If any of your friend's machines need to talk to the extruded subnet,<EM> + they</EM> need to have a route for the extruded subnet, pointing at his + gateway.</P> +<P>Then set up an IPsec subnet-to-subnet tunnel between your gateway and + his, with your subnet specified as the extruded subnet, and his subnet + specified as "0.0.0.0/0".</P> +<P>The tunnel description should be:</P> +<PRE>conn extruded + left=p.q.r.s + leftsubnet=0.0.0.0/0 + right=d.e.f.g + rightsubnet=a.b.c.0/28</PRE> +<P>If either side was doing firewalling for the extruded subnet before + the IPsec connection is set up, you'll need to poke holes in your<A HREF="firewall.html#firewall"> + firewall</A> to allow packets through.</P> +<P>And it all just works. Your SG routes traffic for 0.0.0.0/0 -- that + is, the whole Internet -- through the tunnel to his SG, which then + sends it onward as if it came from his subnet. When traffic for the + extruded subnet arrives at his SG, it gets sent through the tunnel to + your SG, which passes it to the right machine.</P> +<P>Remember that when ipsec_manual or ipsec_auto takes a connection + down, it<EM> does not undo the route</EM> it made for that connection. + This lets you take a connection down and bring up a new one, or a + modified version of the old one, without having to rebuild the route it + uses and without any risk of packets which should use IPsec + accidentally going out in the clear. Because the route always points + into KLIPS, the packets will always go there. Because KLIPS temporarily + has no idea what to do with them (no eroute for them), they will be + discarded.</P> +<P>If you<EM> do</EM> want to take the route down, this is what the + "unroute" operation in manual and auto is for. Just do an unroute after + doing the down.</P> +<P>Note that the route for a connection may have replaced an existing + non-IPsec route. Nothing in Linux FreeS/WAN will put that pre-IPsec + route back. If you need it back, you have to create it with the route + command.</P> +<H2><A name="roadvirt">Road Warrior with virtual IP address</A></H2> +<P>Please note that<A HREF="http://www.freeswan.ca/download.php"> Super + FreeS/WAN</A> now features DHCP-over-IPsec, which is an alternate + procedure for Virtual IP address assignment.</P> +<P></P> +<P>Here is a mailing list message about another way to configure for + road warrior support:</P> +<PRE>Subject: Re: linux-ipsec: understanding the vpn + Date: Thu, 28 Oct 1999 10:43:22 -0400 + From: Irving Reid <irving@nevex.com> + +> local-------linux------internet------mobile +> LAN box user +> ... + +> now when the mobile user connects to the linux box +> it is given a virtual IP address, i have configured it to +> be in the 10.x.x.x range. mobile user and linux box +> have a tunnel between them with these IP addresses. + +> Uptil this all is fine. + +If it is possible to configure your mobile client software *not* to +use a virtual IP address, that will make your life easier. It is easier +to configure FreeS/WAN to use the actual address the mobile user gets +from its ISP. + +Unfortunately, some Windows clients don't let you choose. + +> what i would like to know is that how does the mobile +> user communicate with other computers on the local +> LAN , of course with the vpn ? + +> what IP address should the local LAN +> computers have ? I guess their default gateway +> should be the linux box ? and does the linux box need +> to be a 2 NIC card box or one is fine. + +As someone else stated, yes, the Linux box would usually be the default +IP gateway for the local lan. + +However... + +If you mobile user has software that *must* use a virtual IP address, +the whole picture changes. Nobody has put much effort into getting +FreeS/WAN to play well in this environment, but here's a sketch of one +approach: + +Local Lan 1.0.0.0/24 + | + +- Linux FreeS/WAN 1.0.0.2 + | + | 1.0.0.1 + Router + | 2.0.0.1 + | +Internet + | + | 3.0.0.1 +Mobile User + Virtual Address: 1.0.0.3 + +Note that the Local Lan network (1.0.0.x) can be registered, routable +addresses. + +Now, the Mobile User sets up an IPSec security association with the +Linux box (1.0.0.2); it should ESP encapsulate all traffic to the +network 1.0.0.x **EXCEPT** UDP port 500. 500/udp is required for the key +negotiation, which needs to work outside of the IPSec tunnel. + +On the Linux side, there's a bunch of stuff you need to do by hand (for +now). FreeS/WAN should correctly handle setting up the IPSec SA and +routes, but I haven't tested it so this may not work... + +The FreeS/WAN conn should look like: + +conn mobile + right=1.0.0.2 + rightsubnet=1.0.0.0/24 + rightnexthop=1.0.0.1 + left=0.0.0.0 # The infamous "road warrior" + leftsubnet=1.0.0.3/32 + +Note that the left subnet contains *only* the remote host's virtual +address. + +Hopefully the routing table on the FreeS/WAN box ends up looking like +this: + +% netstat -rn +Kernel IP routing table +Destination Gateway Genmask Flags MSS Window irtt Iface +1.0.0.0 0.0.0.0 255.255.255.0 U 1500 0 0 eth0 +127.0.0.0 0.0.0.0 255.0.0.0 U 3584 0 0 lo +0.0.0.0 1.0.0.1 0.0.0.0 UG 1500 0 0 eth0 +1.0.0.3 1.0.0.1 255.255.255.255 UG 1433 0 0 ipsec0 + +So, if anybody sends a packet for 1.0.0.3 to the Linux box, it should +get bundled up and sent through the tunnel. To get the packets for +1.0.0.3 to the Linux box in the first place, you need to use "proxy +ARP". + +How this works is: when a host or router on the local Ethernet segment +wants to send a packet to 1.0.0.3, it sends out an Ethernet level +broadcast "ARP request". If 1.0.0.3 was on the local LAN, it would +reply, saying "send IP packets for 1.0.0.3 to my Ethernet address". + +Instead, you need to set up the Linux box so that _it_ answers ARP +requests for 1.0.0.3, even though that isn't its IP address. That +convinces everyone else on the lan to send 1.0.0.3 packets to the Linux +box, where the usual FreeS/WAN processing and routing take over. + +% arp -i eth0 -s 1.0.0.3 -D eth0 pub + +This says, if you see an ARP request on interface eth0 asking for +1.0.0.3, respond with the Ethernet address of interface eth0. + +Now, as I said at the very beginning, if it is *at all* possible to +configure your client *not* to use the virtual IP address, you can avoid +this whole mess.</PRE> +<H2><A name="dynamic">Dynamic Network Interfaces</A></H2> +<P>Sometimes you have to cope with a situation where the network + interface(s) aren't all there at boot. The common example is notebooks + with PCMCIA.</P> +<H3><A name="basicdyn">Basics</A></H3> +<P>The key issue here is that the<VAR> config setup</VAR> section of the<VAR> + /etc/ipsec.conf</VAR> configuration file lists the connection between + ipsecN and hardware interfaces, in the<VAR> interfaces=</VAR> variable. + At any time when<VAR> ipsec setup start</VAR> or<VAR> ipsec setup + restart</VAR> is run this variable<STRONG> must</STRONG> correspond to + the current real situation. More precisely, it<STRONG> must not</STRONG> + mention any hardware interfaces which don't currently exist. The + difficulty is that an<VAR> ipsec setup start</VAR> command is normally + run at boot time so interfaces that are not up then are mis-handled.</P> +<H3><A name="bootdyn">Boot Time</A></H3> +<P>Normally, an<VAR> ipsec setup start</VAR> is run at boot time. + However, if the hardware situation at boot time is uncertain, one of + two things must be done.</P> +<UL> +<LI>One possibility is simply not to have IPsec brought up at boot time. + To do this: +<PRE> chkconfig --level 2345 ipsec off</PRE> + That's for modern Red Hats or other Linuxes with chkconfig. Systems + which lack this will require fiddling with symlinks in /etc/rc.d/rc?.d + or the equivalent.</LI> +<LI>Another possibility is to bring IPsec up with no interfaces, which + is less aesthetically satisfying but simpler. Just put +<PRE> interfaces=</PRE> + in the configuration file. KLIPS and Pluto will be started, but won't + do anything.</LI> +</UL> +<H3><A name="changedyn">Change Time</A></H3> +<P>When the hardware *is* in place, IPsec has to be made aware of it. + Someday there may be a nice way to do this.</P> +<P>Right now, the way to do it is to fix the<VAR> /etc/ipsec.conf</VAR> + file appropriately, so<VAR> interfaces</VAR> reflects the new + situation, and then restart the IPsec subsystem. This does break any + existing IPsec connections.</P> +<P>If IPsec wasn't brought up at boot time, do</P> +<PRE> ipsec setup start</PRE> + while if it was, do +<PRE> ipsec setup restart</PRE> + which won't be as quick. +<P>If some of the hardware is to be taken out, before doing that, amend + the configuration file so interfaces no longer includes it, and do</P> +<PRE> ipsec setup restart</PRE> +<P>Again, this breaks any existing connections.</P> +<H2><A name="unencrypted">Unencrypted tunnels</A></H2> +<P>Sometimes you might want to create a tunnel without encryption. Often + this is a bad idea, even if you have some data which need not be + private. See this<A href="ipsec.html#traffic.resist"> discussion</A>.</P> +<P>The IPsec protocols provide two ways to do build such tunnels:</P> +<DL> +<DT>using ESP with null encryption</DT> +<DD>not supported by FreeS/WAN</DD> +<DT>using<A href="glossary.html#AH"> AH</A> without<A href="glossary.html#ESP"> + ESP</A></DT> +<DD>supported for manually keyed connections</DD> +<DD>possible with explicit commands via<A href="manpage.d/ipsec_whack.8.html"> + ipsec_whack(8)</A> (see this<A href="http://www.sandelman.ottawa.on.ca/linux-ipsec/html/2001/02/msg00190.html"> + list message</A>)</DD> +<DD>not supported in the<A href="manpage.d/ipsec_auto.8.html"> + ipsec_auto(8)</A> scripts.</DD> +</DL> + One situation in which this comes up is when otherwise some data would + be encrypted twice. Alice wants a secure tunnel from her machine to + Bob's. Since she's behind one security gateway and he's behind another, + part of the tunnel that they build passes through the tunnel that their + site admins have built between the gateways. All of Alice and Bob's + messages are encrypted twice. +<P>There are several ways to handle this.</P> +<UL> +<LI>Just accept the overhead of double encryption. The site admins might + choose this if any of the following apply: +<UL> +<LI>policy says encrypt everything (usually, it should)</LI> +<LI>they don't entirely trust Alice and Bob (usually, if they don't have + to, they shouldn't)</LI> +<LI>if they don't feel the saved cycles are worth the time they'd need + to build a non-encrypted tunnel for Alice and Bob's packets (often, + they aren't)</LI> +</UL> +</LI> +<LI>Use a plain IP-in-IP tunnel. These are not well documented. A good + starting point is in the Linux kernel source tree, in + /usr/src/linux/drivers/net/README.tunnel.</LI> +<LI>Use a manually-keyed AH-only tunnel.</LI> +</UL> +<P>Note that if Alice and Bob want end-to-end security, they must build + a tunnel end-to-end between their machines or use some other end-to-end + tool such as PGP or SSL that suits their data. The only question is + whether the admins build some special unencrypted tunnel for those + already-encrypted packets.</P> +<HR> +<A HREF="toc.html">Contents</A> +<A HREF="kernel.html">Previous</A> +<A HREF="install.html">Next</A> +</BODY> +</HTML> |