EPDG implementation plan » History » Version 18
laforge, 02/05/2024 04:40 PM
1 | 2 | laforge | {{>toc}} |
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3 | 1 | laforge | h1. EPDG implementation plan |
4 | 2 | laforge | |
5 | h2. The big picture |
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6 | |||
7 | Ideally, we want to reuse existing code whenever possible, rather than reinvent the wheel. Time will tell, if this works out or if we have to rewrite more of it. |
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8 | * StrongSwan charon for handling IKEv2 and managing the IPsec SAs in the kernel IPsec |
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9 | * Erlang DIAMETER application for all the related interfaces |
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10 | * Erlang gtplib for S2b |
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11 | |||
12 | This means we will have two major "applications" running: |
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13 | * charon |
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14 | * ePDG (likely in Erlang) |
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15 | |||
16 | Between those two we will need some kind of non-standard, custom interface. For now I've called it "CEAI" for (Charon External AKA Interface) |
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17 | |||
18 | h2. Control Plane |
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19 | |||
20 | * *red* color indicates elements / interfaces to be implemented. |
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21 | |||
22 | {{graphviz_link() |
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23 | digraph G { |
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24 | rankdir=LR; |
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25 | subgraph cluster_swan { |
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26 | label = "StrongSWAN domain"; |
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27 | charon; |
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28 | } |
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29 | subgraph cluster_erlang { |
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30 | label = "Erlang domain"; |
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31 | ePDG [color=red]; |
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32 | AAA [label="3GPP AAA Server", color=red]; |
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33 | } |
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34 | HSS; |
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35 | PGW; |
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36 | 14 | pespin | PCRF; |
37 | 2 | laforge | UE; |
38 | |||
39 | charon -> ePDG [label="CEAI", color=red]; |
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40 | |||
41 | UE -> charon [label="IKEv2"]; |
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42 | ePDG -> AAA [label="SWm (DIAMETER)", color=red]; |
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43 | AAA -> HSS [label="SWx (DIAMETER)", color=red]; |
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44 | 14 | pespin | PGW -> AAA [label="S6b (DIAMETER)", color=red]; |
45 | 2 | laforge | |
46 | ePDG -> PGW [label="S2b (GTPv2C)", color=red]; |
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47 | 1 | laforge | ePDG -> PCRF [label="Gxb", color=red, style=dashed]; |
48 | PGW -> PCRF [label="Gx (DIAMETER)"]; |
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49 | 14 | pespin | |
50 | {rank=same; PCRF; HSS} |
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51 | 2 | laforge | } |
52 | }} |
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53 | |||
54 | h2. User Plane |
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55 | |||
56 | * *red* color indicates elements / interfaces to be implemented. |
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57 | * *blue* color indicates control-plane elements controlling the user plane |
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58 | |||
59 | {{graphviz_link() |
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60 | digraph G { |
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61 | rankdir=LR; |
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62 | |||
63 | subgraph cluster_swan { |
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64 | label = "StrongSWAN domain"; |
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65 | { rank=same; |
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66 | ipsec [label="Linux kernel\nIPsec"]; |
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67 | charon [color=blue]; |
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68 | } |
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69 | charon -> ipsec [label="netlink", color=blue]; |
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70 | } |
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71 | subgraph cluster_erlang { |
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72 | label = "Erlang domain"; |
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73 | { rank=same |
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74 | gtp [label="Linux kernel\nGTP"]; |
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75 | ePDG [color="blue"]; |
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76 | } |
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77 | ePDG -> gtp [label="netlink", color=blue]; |
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78 | } |
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79 | PGW; |
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80 | UE; |
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81 | |||
82 | UE -> ipsec [label="ESP/UDP"]; |
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83 | ipsec->gtp [label="kernel IP stack"]; |
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84 | gtp -> PGW [label="S2b (GTPv1U)", color=red]; |
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85 | } |
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86 | }} |
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87 | |||
88 | 16 | laforge | h3. At system startup |
89 | |||
90 | * set the various routes |
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91 | * on @epdg@ node |
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92 | 17 | laforge | ** osmo-epdg creates the @gtp0@ net-device (in GTP_ROLE_SGSN) via netlink |
93 | 16 | laforge | * on @epc@ node |
94 | ** open5gs-upf creates the @tun0@ net-device |
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95 | |||
96 | h3. When a user authenticates via IPsec |
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97 | |||
98 | * on @epdg@ node |
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99 | ** osmo-epdg creates a new GTP tunnel entry within the GTP link |
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100 | 18 | laforge | *** GTPA_PEER_ADDRESS/ADDR6 = pgw-ip |
101 | *** GTPA_MS_ADDRESS/MS_ADDR6 = ue-ip (inner) |
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102 | *** GTPA_I_TEI = epdg-teid |
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103 | *** GTPA_O_TEI = pgw-teid |
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104 | 16 | laforge | * on @epc@ node |
105 | ** open5gs-upf creates a new GTP tunnel entry within its internal state tables |
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106 | |||
107 | h3. Uplink traffic (e.g. from UE to P-CSCF) |
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108 | |||
109 | * one @epdg@ node |
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110 | ** IPsec-encapsulated traffic from the UE side enters as IPv6-in-ESP-in-UDP-in-IP[v4/v6] on the public/internet-facing side |
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111 | ** kernel-IPsec (configured by strongswan) will transform (decrypt, ...) the traffic |
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112 | *** we configure strongswan to mark the ipsec-originated traffic with a certain fwmark |
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113 | ** traffic with that fwmark is routed (using a statically configured @ip rule@) towards the @gtp0@ net-device (created by osmo-epdg at startup) |
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114 | ** linux kernel GTP tunnel module |
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115 | *** looks up the in-kernel table to determine destination TEID and destination IP address based on the MS-side source address |
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116 | *** encapsulates packet in GTP header and sends it through the in-kernel UDP socket to the PGW |
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117 | * on the @epc@ node |
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118 | ** (open5gs-)pgw matches inbound packet based on (dest-ip + TEID) with its internal state table |
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119 | ** (open5gs-)pgw decapsulates packet from GTP header |
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120 | ** (open5gs-)pgw exposes inner IPv6 packet on @tun0@ net-device |
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121 | ** linux kernel routes packet towards P-CSCF (inner IPv6 dest IP address as originally set by UE) |
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122 | * on the @ims@ node |
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123 | ** linux kernel routes packet towards local P-CSCF socket |
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124 | |||
125 | h3. Downlink traffic (e.g. from P-CSCF to UE) |
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126 | |||
127 | * on @ims@ node |
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128 | ** IPv6 packet from P-CSCF is sent to UE IPv6 address |
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129 | ** large network route (for all UE) points towards @epc@ node |
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130 | * on @epc@ node |
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131 | ** traffic to UE IPv6 is routed into @tun0@ net-device |
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132 | ** (open5gs-)pgw looks up destination-ip and TEID |
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133 | ** (open5gs-)pwg encapsulates packet with GTP-U header and sends it via UDP socket |
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134 | ** linux kernel routes it towards the ePDG |
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135 | * on @epdg@ node |
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136 | ** linux kernel routes GTP packet to locally bound UDP socket and detects the kernel GTP driver is bound to that socket |
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137 | ** linux kernel GTP driver performs lookup based on dest-ip and TEID |
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138 | ** linux kernel de-capsulates GTP packet and exposes inner packet on @gtp0@ net-device |
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139 | ** linux kernel IPsec code applies transformation (crypto) and ESP-in-UDP-encapsulation |
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140 | * packet is routed towards UE |
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141 | 5 | lynxis | |
142 | h2. Authentication |
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143 | |||
144 | !ipsec_auth.png! |
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145 | |||
146 | 3 | laforge | h2. 3GPP Interfaces and Procedures |
147 | 2 | laforge | |
148 | h3. ePDG |
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149 | |||
150 | 1 | laforge | |
151 | 6 | lynxis | h4. S2b to PGW (GTPv2C) [TS 29.274] |
152 | 2 | laforge | |
153 | h5. Create Session Request / Response |
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154 | |||
155 | h5. Delete Session Request / Response |
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156 | |||
157 | h5. Modify Bearer Request / Respone (not needed?) |
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158 | |||
159 | h5. Modify Bearere Command (not needed?) |
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160 | |||
161 | h5. Bearer Resource Command (not needed?) |
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162 | |||
163 | h5. Create Bearer Request / Response |
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164 | |||
165 | h5. Update Bearer Request / Response (not needed?) |
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166 | |||
167 | |||
168 | 9 | pespin | h4. SWm to AAA (DIAMETER) [3GPP TS 29.273] |
169 | 2 | laforge | |
170 | h5. Diameter-EAP-Request (DER) / Diameter-EAP-Response (DEA) |
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171 | |||
172 | h5. Diameter-AA-Request (AAR) / Diameter-AA-Response (AAA) |
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173 | |||
174 | h5. Session-Termination-Request (STR) / Session-Termination-Answer (STA) |
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175 | |||
176 | h5. Re-Auth-Requst (RAR) / Re-Auth-Answer (RAA) |
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177 | |||
178 | h5. Abort-Session-Request (ASR) / Abort-Session-Answer (ASA) |
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179 | |||
180 | 12 | pespin | h4. SWu to UE (IKEv2, ESP) [3GPP TS 33.402] |
181 | 2 | laforge | |
182 | 11 | pespin | * Related: https://fabricioapps.blogspot.com/2017/10/untrusted-non-3gpp-ip-access-swu-ikev2.html |
183 | 2 | laforge | |
184 | h4. Gxb to PCRF (not needed?) |
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185 | |||
186 | |||
187 | h3. 3GPP AAA Server |
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188 | |||
189 | 10 | pespin | h4. SWx to HSS (DIAMETER) [3GPP TS 29.273 sec 8, 3GPP TS 23.402 sec 12] |
190 | 2 | laforge | |
191 | h5. Push-Profile-Request (PPR) / Push-Profile-Answer (PPA) |
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192 | |||
193 | h5. Registration-Termination-Request (RTR) / Registration-Termination-Answer (RTA) |
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194 | |||
195 | h5. Multimedia-Auth-Request (MAR) / Multimedia-Auth-Answer (MAA) |
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196 | |||
197 | 7 | pespin | * 3GPP TS 29.273 8.2.2.1 |
198 | 8 | pespin | * https://www.etsi.org/deliver/etsi_ts/129200_129299/129273/17.06.00_60/ts_129273v170600p.pdf |
199 | 7 | pespin | * https://dstest.info/DiaDict/Dictionary/Multimedia-Auth-Request_SWx.html |
200 | |||
201 | 2 | laforge | h5. Server-Assignment-Request (SAR) / Server-Assignment-Answer (SAA) |
202 | |||
203 | 13 | pespin | h4. S6b to PGW (DIAMETER) [3GPP TS 29.273 sec 9] |
204 | 2 | laforge | |
205 | 13 | pespin | * https://osmocom.org/issues/6229 |
206 | 2 | laforge | |
207 | h4. SWm to ePDG (DIAMETER) |
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208 | |||
209 | 1 | laforge | see above. |
210 | 3 | laforge | |
211 | |||
212 | 4 | lynxis | h3. custom Interfaces / Procedures |
213 | |||
214 | h4. CEAI |
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215 | |||
216 | FIXME |
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217 | 15 | pespin | |
218 | h3. Related information links |
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219 | |||
220 | * https://www.cisco.com/c/en/us/td/docs/wireless/asr_5000/21-23/PGW-Admin/21-23-pgw-admin/21-16-PGW-Admin_chapter_011001.html |