1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
|
<?xml version='1.0'?>
<!DOCTYPE rfc SYSTEM 'rfcXXXX.dtd' [
<!ENTITY rfc1546 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1546.xml'>
<!ENTITY rfc3711 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3711.xml'>
<!ENTITY rfc3068 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3068.xml'>
<!ENTITY rfc2784 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2784.xml'>
<!ENTITY rfc2401 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2401.xml'>
<!ENTITY rfc2119 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'>
<!ENTITY rfc2003 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2003.xml'>
]>
<?rfc toc='yes'?>
<rfc ipr='full3978' docName='draft-gsenger-secure-anycast-tunneling-protocol-00'>
<front>
<title>secure anycast tunneling protocol (SATP)</title>
<author initials='O.G.' surname='Gsenger'
fullname='Othmar Gsenger'>
<organization></organization>
<address>
<postal>
<street>Puerstingerstr 32</street>
<city>Saalfelden</city>
<code>5760</code>
<country>AT</country>
</postal>
<phone></phone>
<email>satp@gsenger.com</email>
<uri>http://www.gsenger.com/satp/</uri>
</address>
</author>
<date month='April' year='2007' />
<area>General</area>
<workgroup></workgroup>
<keyword>satp</keyword>
<keyword>Internet-Draft</keyword>
<keyword>secure anycast tunneling protocol</keyword>
<keyword>anycast</keyword>
<keyword>tunnel</keyword>
<keyword>secure</keyword>
<keyword>protocol</keyword>
<abstract>
<t>The secure anycast tunneling protocol (SATP) defines a protocol used for communication between any combination of unicast and anycast tunnel endpoints. It allows tunneling of every ETHER TYPE protocol (e.g. ethernet, ip, arp ...). SATP directly includes cryptography and message authentication based on the methodes used by SRTP. It is intended to deliver a generic, scaleable and secure solution for tunneling and relaying of packets of any protocol.
</t>
</abstract>
</front>
<middle>
<section title='Introduction'>
<t>SATP is somehow a mixture of a generic encapsulation protocol like <xref target="RFC2784">GRE</xref> and a secure tunneling protocol as <xref target="RFC2401">IPsec</xref> in tunnel mode. To save some header overhead it uses the encryption technices of <xref target="RFC3711">SRTP</xref>. It supports peer to peer tunnels, where tunnel endpoints can be any combination of unicast, multicast or anycast hosts, so it defines a <xref target="RFC1546">Host Anycast Service</xref></t>
<section title='Notational Conventions'>
<t>The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target="RFC2119">RFC2119</xref>.</t>
</section>
</section>
<section title="Motivation and usage scenarios">
<t>This section gives an overview of possible usage scenarios. Please note, that the protocols used in the figures are only examples and that SATP itself does not care about either transport protocols or encapsulated protocols. Routing is not done by SATP and each implemetation MAY choose it's own way of doing this task (e.g. using functions provided by the operating system). SATP is used only to encapsulate and encrypt data.</t>
<section title="Usage scenarions">
<section title='Tunneling from unicast hosts over anycast routers to other unicast hosts'>
<figure anchor="tunnel_mode">
<preamble>An example of SATP used to tunnel in a unicast client - anycast server model</preamble>
<artwork>
--------- router -----------
/ \
unicast ------+---------- router ------------+------ unicast
host \ / host
--------- router -----------
unicast | encrypted | anycast | encrypted | unicast
tunnel | communication | tunnel | communication | tunnel
endpoint | using SATP | endpoint | using SATP | endpoint
</artwork>
</figure>
<t>In this scenario the payload gets encapsuleted into a SATP packet by a unicast host and gets transmitted to one of the anycast routers. It than gets decapsulated by the router. This router makes a routing descision based on the underlying protocol and transmits a new SATP package to one or more unicast hosts depending on the routing descition.</t>
</section>
<section title='Tunneling from unicast hosts to anycast networks'>
<figure anchor="open_tunnel_mode">
<preamble>An example of SATP used to encrypt data between a unicast host and anycast networks</preamble>
<artwork>
-------Router -+---- DNS Server
/ \
/ --- 6to4 Router
/
unicast -------+----------Router --+--- DNS Server
host \ \
\ --- 6to4 Router
\
-------Router -+---- DNS Server
\
--- 6to4 Router
unicast | encrypted | anycast | plaintext
tunnel | communication | tunnel | anycast
endpoint | using SATP | endpoint | services
</artwork>
</figure>
<t>When the unicast hosts wants to transmit data to one of the anycast DNS servers, it encapsulates the data and sends a SATP packet to the anycast address of the routers. The packet arrives at one of the routers, gets decapsulated and routed to the DNS server. This method can be used to tunnel between a clients and networks providing anycast services. It can also be used the other way to virtually locate a unicast service within anycasted networks.</t>
</section>
<section title='Redundant tunnel connection of 2 networks'>
<figure anchor="connect_networks">
<preamble>An example of SATP used to connect 2 networks</preamble>
<artwork>
Router ----------- ---------------Router
/ \ / \
Network - Router ------------x Network
A \ / \ / B
Router ----------- ---------------Router
| packets | packets | packets |
plaintext | get | take a | get | plaintext
packets | de/encrypted | random | de/encrypted | packets
|de/encapsulated| path |de/encapsulated|
</artwork>
</figure>
<t>Network A has multiple routers, that act as gateway/tunnel endpoints to another network B. This is done to build a redundant encrypted tunnel connection between the two networks. All tunnel endpoints of network A share the same anycast address and all tunnel endpoints of network B share another anycast address. When a packet from network A gets transmitted to network B, it first arrives on one of network A's border routers. Which router is used is determined by network A's internal routing. This router encapsulates the package and sends it to the anycast address of the network B routers. The SATP packet arrives at one of network B's routers and gets decapsulated and routed to it's destination within network B.</t>
</section>
</section>
<section title="Encapsulation">
<t>SATP does not depend on which lower layer protocols is used, but this section gives an example of how packets could look like.
</t>
<figure anchor="transport_udp">
<preamble>Examples of SATP used with different lower layer and payload protocols</preamble>
<artwork>
+------+-----+-------------------------------+
| | | + ---------------+------ |
| IPv6 | UDP | SATP | Ethernet 802.3 | ... | |
| | | +----------------+-----+ |
+------+-----+-------------------------------+
Tunneling of Ethernet over UDP/IPv6
+------+-----+---------------------------+
| | | +------+-----+-----+ |
| IPv4 | UDP | SATP | IPv6 | UDP | RTP | |
| | | +------+-----+-----+ |
+------+-----+---------------------------+
Tunneling of IPv6 over UDP/IPv4 with RTP payload
+------+-------------------------------+
| | + ---------------+------ |
| IPv6 | SATP | Ethernet 802.3 | ... | |
| | +----------------+-----+ |
+------+-------------------------------+
Tunneling of Ethernet over IPv6
+------+---------------------------+
| | +------+-----+-----+ |
| IPv4 | SATP | IPv6 | UDP | RTP | |
| | +------+-----+-----+ |
+------+---------------------------+
Tunneling of IPv6 over IPv4 with RTP payload
</artwork>
</figure>
</section>
</section>
<section title="Using SATP on top of IP">
<section title="Fragmentation">
<t>
The only way of fully supporting fragmentation would be to synchronise fragments between all anycast servers. This is considered to be too much overhead, so there are two non perfect solutions for these problems. Either fragmentation HAS TO be disabled or if not all fragments arrive at the same server the ip datagramm HAS TO be discarded. As routing changes are not expected to occure very frequently, the encapsulated protocol can do a retransmission and all fragments will arrive at the new server.
</t><t>If the payload ip headers's Don't Fragment (DF) bit is set, than the DF bit of the outer ip header HAS TO be set as well.</t>
</section>
<section title="ICMP messages">
<t>ICMP messages MUST be relayed according to <xref target="RFC2003">rfc2003 section 4</xref>. This is needed for path MTU dedection.</t>
</section>
</section>
<section title="Protocol specification">
<section title="Header format">
<figure anchor="prot_header_table">
<preamble>Protocol Format</preamble>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sequence number | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ |
| sender ID # | |
+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ + |
| | .... payload ... | |
| |-------------------------------+-------------------------------+ |
| | padding (OPT) | pad count(OPT)| payload type | |
+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+-+
| ~ MKI (OPTIONAL) ~ |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| : authentication tag (RECOMMENDED) : |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
+- Encrypted Portion Authenticated Portion ---+
</artwork>
</figure>
<t></t>
</section>
<section title="sender ID">
<t>The sender ID is a 16bit unsigned integer. It HAS TO be unique for every sender sharing the same anycast address</t>
</section>
<section title="sequence number">
<t>The sequence number is a 32 bit unsigned integer in network byte order. It starts with a random value and is increased by 1 for every sent packet. After the maximum value, it starts over from 0. This overrun causes the ROC to be increased.</t>
</section>
<section title="payload">
<t>A packet of the type payload type (e.g. an IP packet).</t>
</section>
<section title="padding (OPTIONAL)">
<t>Padding of max 255 octets.
None of the pre-defined encryption transforms uses any padding; for
these, the plaintext and encrypted payload sizes match exactly. Transforms are based on transforms of the SRTP protocol and these transforms might use the RTP padding format, so a RTP like padding is supported. If padding field is present, than the padding count field MUST be set to the padding lenght.</t>
</section>
<section title="padding count">
<t>The number of octets of the padding field. This field is optional. It's presence is signaled by the key management and not by this protocol. If this field isn't present, the padding field MUST NOT be present as well.</t>
</section>
<section title="payload type field">
<t>The payload type field defines the payload protocol. ETHER TYPE protocol numbers are used. <eref target="http://www.iana.org/assignments/ethernet-numbers">See IANA assigned ethernet numbers</eref> . The values 0000-05DC are reserverd and MUST NOT be used.
<figure anchor="prot_type_table">
<preamble>Some examples for protocol types</preamble>
<artwork>
HEX
0000 Reserved
.... Reserved
05DC Reserved
0800 Internet IP (IPv4)
6558 transparent ethernet bridging
86DD IPv6
</artwork>
</figure>
<section title="MKI">
<t>The MKI (Master Key Identifier) is OPTIONAL and of configurable length. See <xref target="RFC3711">SRTP Section 3.1</xref> for details</t>
</section>
<section title="authentication tag">
<t>The authentication tag is RECOMMENDED and of configurable length. It contains a cryptographic checksum of the sender ID, sequence number and the encrypted portion, but not of the MKI. On sender side encryption HAS TO be done before calculating the authentication tag. A receiver HAS TO calculate the authentication tag before decrypting the encrypted portion.</t>
</section>
</t>
</section>
<section title="Encryption">
<t>Encryption is done in the same way as for <xref target="RFC3711">SRTP</xref>. This section will only discuss some small changes that HAVE TO be made. Please read <xref target="RFC3711">SRTP RFC3711 section 3-9</xref> for details. </t><t>The least significant bits of SSRC are replaced by the sender ID and the rest is filled with zeros. For the SRTP SEQ the 16 least significant bits of the SATP sequence number are used and the 16 most significant bits of the sequence number replace the 16 least significant bits of the SRTP ROC.</t>
<figure anchor="srtp_vs_satp">
<preamble>Difference between SRTP and SATP</preamble>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SATP sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
=
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRTP ROC least significant | SRTP SEQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| SATP sender ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
=
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRTP SSRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
<section title="Security Considerations">
<t>As SATP uses the same encrytion technics as <xref target="RFC3711">SRTP</xref>, it shares the same security issues. This section will only discuss some small changes. Please read <xref target="RFC3711">SRTP RFC3711 section 9</xref> for details.</t>
<section title="Replay protection">
<t>Replay protection is done by a replay list. Every anycast receiver has it's own replay list, which SOULDN'T be syncronised, because of massive overhead. This leads to an additional possible attack. A attacker is able to replay a captured packet once to every anycast reciever. This attack is considered of be very unlikely, because multiple attack hosts in different loactions are needed to reach the seperate anycast receivers and the number of replays is limited to the count of receivers - 1. Such replays might also happen because of routing problems, so a payload protocol HAS TO be robust against a small number of duplicated packages. The window size and position HAS TO be syncronised between multible anycast receivers to limit this attack.</t>
</section>
</section>
<section title="IANA Considerations">
<t>To use the protocol on top of UDP and IP protocol numberes have to be assiged by IANA.</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc3711;
&rfc2119;
&rfc2003;
</references>
<references title="Informational References">
&rfc2784;
&rfc2401;
&rfc1546;
</references>
</back>
</rfc>
|
