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diff --git a/doc/adv_config.html b/doc/adv_config.html deleted file mode 100644 index 4b779c753..000000000 --- a/doc/adv_config.html +++ /dev/null @@ -1,1232 +0,0 @@ -<!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> |