1 Configuring Open vSwitch for SSL
2 ================================
4 If you plan to configure Open vSwitch to connect across the network to
5 an OpenFlow controller, then we recommend that you configure and
6 enable SSL support in Open vSwitch. SSL support ensures integrity and
7 confidentiality of the OpenFlow connections, increasing network
10 This file explains how to configure an Open vSwitch to connect to an
11 OpenFlow controller over SSL. Refer to INSTALL.Linux for instructions
12 on building Open vSwitch with SSL support. (In particular, you must
13 pass --enable-ssl to the "configure" script to use SSL.)
15 Open vSwitch uses TLS version 1.0 or later (TLSv1), as specified by
16 RFC 2246, which is very similar to SSL version 3.0. TLSv1 was
17 released in January 1999, so all current software and hardware should
20 This document assumes basic familiarity with public-key cryptography
21 and public-key infrastructure.
23 SSL Concepts for OpenFlow
24 -------------------------
26 This section is an introduction to the public-key infrastructure
27 architectures that Open vSwitch supports for SSL authentication.
29 To connect over SSL, every Open vSwitch must have a unique
30 private/public key pair and a certificate that signs that public key.
31 Typically, the Open vSwitch generates its own public/private key pair.
32 There are two common ways to obtain a certificate for a switch:
34 * Self-signed certificates: The Open vSwitch signs its certificate
35 with its own private key. In this case, each switch must be
36 individually approved by the OpenFlow controller(s), since there
37 is no central authority.
39 This is the only switch PKI model currently supported by NOX
42 * Switch certificate authority: A certificate authority (the
43 "switch CA") signs each Open vSwitch's public key. The OpenFlow
44 controllers then check that any connecting switches'
45 certificates are signed by that certificate authority.
47 This is the only switch PKI model supported by the simple
48 OpenFlow controller included with Open vSwitch.
50 Each Open vSwitch must also have a copy of the CA certificate for the
51 certificate authority that signs OpenFlow controllers' keys (the
52 "controller CA" certificate). Typically, the same controller CA
53 certificate is installed on all of the switches within a given
54 administrative unit. There are two common ways for a switch to obtain
55 the controller CA certificate:
57 * Manually copy the certificate to the switch through some secure
58 means, e.g. using a USB flash drive, or over the network with
59 "scp", or even FTP or HTTP followed by manual verification.
61 * Open vSwitch "bootstrap" mode, in which Open vSwitch accepts and
62 saves the controller CA certificate that it obtains from the
63 OpenFlow controller on its first connection. Thereafter the
64 switch will only connect to controllers signed by the same CA
67 Establishing a Public Key Infrastructure
68 ----------------------------------------
70 Open vSwitch can make use of your existing public key infrastructure.
71 If you already have a PKI, you may skip forward to the next section.
72 Otherwise, if you do not have a PKI, the ovs-pki script included with
73 Open vSwitch can help. To create an initial PKI structure, invoke it
78 to create and populate a new PKI directory. The default location for
79 the PKI directory depends on how the Open vSwitch tree was configured
80 (to see the configured default, look for the --dir option description
81 in the output of "ovs-pki --help").
83 The pki directory contains two important subdirectories. The
84 controllerca subdirectory contains controller CA files, including the
87 - cacert.pem: Root certificate for the controller certificate
88 authority. Each Open vSwitch must have a copy of this file to
89 allow it to authenticate valid controllers.
91 - private/cakey.pem: Private signing key for the controller
92 certificate authority. This file must be kept secret. There is
93 no need for switches or controllers to have a copy of it.
95 The switchca subdirectory contains switch CA files, analogous to those
96 in the controllerca subdirectory:
98 - cacert.pem: Root certificate for the switch certificate
99 authority. The OpenFlow controller must have this file to
100 enable it to authenticate valid switches.
102 - private/cakey.pem: Private signing key for the switch
103 certificate authority. This file must be kept secret. There is
104 no need for switches or controllers to have a copy of it.
106 After you create the initial structure, you can create keys and
107 certificates for switches and controllers with ovs-pki. Refer to the
108 ovs-pki(8) manage for complete details. A few examples of its use
111 CONTROLLER KEY GENERATION
113 To create a controller private key and certificate in files named
114 ctl-privkey.pem and ctl-cert.pem, run the following on the machine
115 that contains the PKI structure:
117 % ovs-pki req+sign ctl controller
119 ctl-privkey.pem and ctl-cert.pem would need to be copied to the
120 controller for its use at runtime. If you were to use ovs-controller,
121 the simple OpenFlow controller included with Open vSwitch, then the
122 --private-key and --certificate options, respectively, would point to
125 It is very important to make sure that no stray copies of
126 ctl-privkey.pem are created, because they could be used to impersonate
129 SWITCH KEY GENERATION WITH SELF-SIGNED CERTIFICATES
131 If you are using self-signed certificates (see "SSL Concepts for
132 OpenFlow"), this is one way to create an acceptable certificate for
133 your controller to approve.
135 1. Run the following command on the Open vSwitch itself:
137 % ovs-pki self-sign sc
139 (This command does not require a copy of any of the PKI files
140 generated by "ovs-pki init", and you should not copy them to the
141 switch because some of them have contents that must remain secret
144 The "ovs-pki self-sign" command has the following output:
146 * sc-privkey.pem, the switch private key file. For security,
147 the contents of this file must remain secret. There is
148 ordinarily no need to copy this file off the Open vSwitch.
150 * sc-cert.pem, the switch certificate, signed by the switch's
151 own private key. Its contents are not a secret.
153 2. Optionally, copy controllerca/cacert.pem from the machine that has
154 the OpenFlow PKI structure and verify that it is correct.
155 (Otherwise, you will have to use CA certificate bootstrapping when
156 you configure Open vSwitch in the next step.)
158 3. Configure Open vSwitch to use the keys and certificates (see
159 "Configuring SSL Support", below).
161 SWITCH KEY GENERATION WITH A SWITCH PKI (EASY METHOD)
163 If you are using a switch PKI (see "SSL Concepts for OpenFlow",
164 above), this method of switch key generation is a little easier than
165 the alternate method described below, but it is also a little less
166 secure because it requires copying a sensitive private key from file
167 from the machine hosting the PKI to the switch.
169 1. Run the following on the machine that contains the PKI structure:
171 % ovs-pki req+sign sc switch
173 This command has the following output:
175 * sc-privkey.pem, the switch private key file. For
176 security, the contents of this file must remain secret.
178 * sc-cert.pem, the switch certificate. Its contents are
181 2. Copy sc-privkey.pem and sc-cert.pem, plus controllerca/cacert.pem,
184 3. Delete the copies of sc-privkey.pem and sc-cert.pem on the PKI
185 machine and any other copies that may have been made in transit.
186 It is very important to make sure that there are no stray copies of
187 sc-privkey.pem, because they could be used to impersonate the
190 (Don't delete controllerca/cacert.pem! It is not
191 security-sensitive and you will need it to configure additional
194 4. Configure Open vSwitch to use the keys and certificates (see
195 "Configuring SSL Support", below).
197 SWITCH KEY GENERATION WITH A SWITCH PKI (MORE SECURE)
199 If you are using a switch PKI (see "SSL Concepts for OpenFlow",
200 above), then, compared to the previous method, the method described
201 here takes a little more work, but it does not involve copying the
202 private key from one machine to another, so it may also be a little
205 1. Run the following command on the Open vSwitch itself:
207 % ovs-pki req sc switch
209 (This command does not require a copy of any of the PKI files
210 generated by "ovs-pki init", and you should not copy them to the
211 switch because some of them have contents that must remain secret
214 The "ovs-pki req" command has the following output:
216 * sc-privkey.pem, the switch private key file. For security,
217 the contents of this file must remain secret. There is
218 ordinarily no need to copy this file off the Open vSwitch.
220 * sc-req.pem, the switch "certificate request", which is
221 essentially the switch's public key. Its contents are not a
224 * A fingerprint, on stdout.
226 2. Write the fingerprint down on a slip of paper and copy sc-req.pem
227 to the machine that contains the PKI structure.
229 3. On the machine that contains the PKI structure, run:
231 % ovs-pki sign sc switch
233 This command will output a fingerprint to stdout and request that
234 you verify it. Check that it is the same as the fingerprint that
235 you wrote down on the slip of paper before you answer "yes".
237 "ovs-pki sign" creates a file named sc-cert.pem, which is the
238 switch certificate. Its contents are not a secret.
240 4. Copy the generated sc-cert.pem, plus controllerca/cacert.pem from
241 the PKI structure, to the Open vSwitch, and verify that they were
244 You may delete sc-cert.pem from the machine that hosts the PKI
245 structure now, although it is not important that you do so. (Don't
246 delete controllerca/cacert.pem! It is not security-sensitive and
247 you will need it to configure additional switches.)
249 5. Configure Open vSwitch to use the keys and certificates (see
250 "Configuring SSL Support", below).
252 Configuring SSL Support
253 -----------------------
255 SSL configuration requires three additional configuration files. The
256 first two of these are unique to each Open vSwitch. If you used the
257 instructions above to build your PKI, then these files will be named
258 sc-privkey.pem and sc-cert.pem, respectively:
260 - A private key file, which contains the private half of an RSA or
263 This file can be generated on the Open vSwitch itself, for the
264 greatest security, or it can be generated elsewhere and copied
267 The contents of the private key file are secret and must not be
270 - A certificate file, which certifies that the private key is that
271 of a trustworthy Open vSwitch.
273 This file has to be generated on a machine that has the private
274 key for the switch certification authority, which should not be
275 an Open vSwitch; ideally, it should be a machine that is not
278 The certificate file itself is not a secret.
280 The third configuration file is typically the same across all the
281 switches in a given administrative unit. If you used the
282 instructions above to build your PKI, then this file will be named
285 - The root certificate for the controller certificate authority.
286 The Open vSwitch verifies it that is authorized to connect to an
287 OpenFlow controller by verifying a signature against this CA
290 Once you have these files, configure ovs-vswitchd to use them by
291 adding the following keys to your ovs-vswitchd.conf file:
293 ssl.private-key=/etc/vswitch/sc-privkey.pem
294 ssl.certificate=/etc/vswitch/sc-cert.pem
295 ssl.ca-cert=/etc/vswitch/cacert.pem
297 Substitute the correct file names, of course, if they differ from the
300 If you are using self-signed certificates (see "SSL Concepts for
301 OpenFlow") and you did not copy controllerca/cacert.pem from the PKI
302 machine to the Open vSwitch, then also add the following key:
304 ssl.bootstrap-ca-cert=true
306 After you have added all of these configuration keys, you may specify
307 "ssl:" connection methods elsewhere in ovs-vswitchd.conf, e.g.:
309 mgmt.controller=ssl:192.168.0.1
311 "tcp:" connection methods are still allowed even after SSL has been
312 configured, so for security you should use only "ssl:" connections.
317 Please report problems to bugs@openvswitch.org.