Iptables Tutorial 1.2.2
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- Dedications - Страница 2
- About the author - Страница 3
- How to read - Страница 4
- Prerequisites - Страница 5
- Conventions used in this document - Страница 6
- Chapter 1. Introduction - Страница 7
- How it was written - Страница 8
- Terms used in this document - Страница 9
- What's next? - Страница 10
- Chapter 2. TCP/IP repetition - Страница 11
- TCP/IP Layers - Страница 12
- IP characteristics - Страница 14
- IP headers - Страница 16
- TCP characteristics - Страница 19
- TCP headers - Страница 20
- UDP characteristics - Страница 22
- UDP headers - Страница 23
- ICMP characteristics - Страница 24
- ICMP headers - Страница 25
- ICMP Echo Request/Reply - Страница 26
- ICMP Destination Unreachable - Страница 27
- Source Quench - Страница 28
- Redirect - Страница 29
- TTL equals 0 - Страница 30
- Parameter problem - Страница 31
- Timestamp request/reply - Страница 32
- Information request/reply - Страница 33
- SCTP Characteristics - Страница 34
- Initialization and association - Страница 35
- Data sending and control session - Страница 36
- Shutdown and abort - Страница 37
- SCTP Headers - Страница 38
- SCTP Generic header format - Страница 39
- SCTP Common and generic headers - Страница 40
- SCTP ABORT chunk - Страница 42
- SCTP COOKIE ACK chunk - Страница 43
- SCTP COOKIE ECHO chunk - Страница 44
- SCTP DATA chunk - Страница 45
- SCTP ERROR chunk - Страница 46
- SCTP HEARTBEAT chunk - Страница 47
- SCTP HEARTBEAT ACK chunk - Страница 48
- SCTP INIT chunk - Страница 49
- SCTP INIT ACK chunk - Страница 51
- SCTP SACK chunk - Страница 52
- SCTP SHUTDOWN chunk - Страница 53
- SCTP SHUTDOWN ACK chunk - Страница 54
- SCTP SHUTDOWN COMPLETE chunk - Страница 55
- TCP/IP destination driven routing - Страница 56
- What's next? - Страница 57
- Chapter 3. IP filtering introduction - Страница 58
- What is an IP filter - Страница 59
- IP filtering terms and expressions - Страница 61
- How to plan an IP filter - Страница 63
- What's next? - Страница 65
- Chapter 4. Network Address Translation Introduction - Страница 66
- What NAT is used for and basic terms and expressions - Страница 67
- Caveats using NAT - Страница 68
- Example NAT machine in theory - Страница 69
- What is needed to build a NAT machine - Страница 70
- Placement of NAT machines - Страница 71
- How to place proxies - Страница 72
- The final stage of our NAT machine - Страница 73
- What's next? - Страница 74
- Chapter 5. Preparations - Страница 75
- Where to get iptables - Страница 76
- Kernel setup - Страница 77
- User-land setup - Страница 80
- Compiling the user-land applications - Страница 81
- Installation on Red Hat 7.1 - Страница 82
- What's next? - Страница 84
- Chapter 6. Traversing of tables and chains - Страница 85
- General - Страница 86
- Mangle table - Страница 89
- Nat table - Страница 90
- Raw table - Страница 91
- Filter table - Страница 92
- User specified chains - Страница 93
- What's next? - Страница 94
- Chapter 7. The state machine - Страница 95
- Introduction - Страница 96
- The conntrack entries - Страница 97
- User-land states - Страница 99
- TCP connections - Страница 100
- UDP connections - Страница 102
- ICMP connections - Страница 103
- Default connections - Страница 105
- Untracked connections and the raw table - Страница 106
- Complex protocols and connection tracking - Страница 107
- What's next? - Страница 109
- Chapter 8. Saving and restoring large rule-sets - Страница 110
- Speed considerations - Страница 111
- Drawbacks with restore - Страница 112
- iptables-save - Страница 113
- iptables-restore - Страница 115
- What's next? - Страница 116
- Chapter 9. How a rule is built - Страница 117
- Basics of the iptables command - Страница 118
- Tables - Страница 119
- Commands - Страница 120
- What's next? - Страница 122
- Chapter 10. Iptables matches - Страница 123
- Generic matches - Страница 124
- Implicit matches - Страница 125
- TCP matches - Страница 126
- UDP matches - Страница 127
- ICMP matches - Страница 128
- SCTP matches - Страница 129
- Explicit matches - Страница 131
- Addrtype match - Страница 132
- AH/ESP match - Страница 133
- Comment match - Страница 134
- Connmark match - Страница 135
- Conntrack match - Страница 136
- Dscp match - Страница 137
- Ecn match - Страница 138
- Hashlimit match - Страница 139
- Helper match - Страница 140
- IP range match - Страница 141
- Length match - Страница 142
- Limit match - Страница 143
- Mac match - Страница 144
- Mark match - Страница 145
- Multiport match - Страница 146
- Owner match - Страница 147
- Packet type match - Страница 148
- Realm match - Страница 149
- Recent match - Страница 150
- State match - Страница 152
- Tcpmss match - Страница 153
- Tos match - Страница 154
- Ttl match - Страница 155
- Unclean match - Страница 156
- What's next? - Страница 157
- Chapter 11. Iptables targets and jumps - Страница 158
- ACCEPT target - Страница 159
- CLASSIFY target - Страница 160
- CLUSTERIP target - Страница 161
- CONNMARK target - Страница 163
- CONNSECMARK target - Страница 164
- DNAT target - Страница 165
- DROP target - Страница 168
- DSCP target - Страница 169
- ECN target - Страница 170
- LOG target options - Страница 171
- MARK target - Страница 172
- MASQUERADE target - Страница 173
- MIRROR target - Страница 174
- NETMAP target - Страница 175
- NFQUEUE target - Страница 176
- NOTRACK target - Страница 177
- QUEUE target - Страница 178
- REDIRECT target - Страница 179
- REJECT target - Страница 180
- RETURN target - Страница 181
- SAME target - Страница 182
- SECMARK target - Страница 183
- SNAT target - Страница 184
- TCPMSS target - Страница 185
- TOS target - Страница 186
- TTL target - Страница 187
- ULOG target - Страница 188
- What's next? - Страница 189
- Chapter 12. Debugging your scripts - Страница 190
- Debugging, a necessity - Страница 191
- Bash debugging tips - Страница 192
- System tools used for debugging - Страница 194
- Iptables debugging - Страница 195
- Other debugging tools - Страница 196
- Nmap - Страница 197
- Nessus - Страница 198
- What's next? - Страница 199
- Chapter 13. rc.firewall file - Страница 200
- example rc.firewall - Страница 201
- explanation of rc.firewall - Страница 202
- Initial loading of extra modules - Страница 203
- proc set up - Страница 205
- Displacement of rules to different chains - Страница 206
- Setting up default policies - Страница 208
- Setting up user specified chains in the filter table - Страница 209
- INPUT chain - Страница 212
- FORWARD chain - Страница 214
- OUTPUT chain - Страница 215
- PREROUTING chain of the nat table - Страница 216
- Starting SNAT and the POSTROUTING chain - Страница 217
- What's next? - Страница 218
- Chapter 14. Example scripts - Страница 219
- rc.firewall.txt script structure - Страница 220
- The structure - Страница 221
- rc.firewall.txt - Страница 224
- rc.DMZ.firewall.txt - Страница 225
- rc.DHCP.firewall.txt - Страница 226
- rc.UTIN.firewall.txt - Страница 228
- rc.test-iptables.txt - Страница 229
- rc.flush-iptables.txt - Страница 230
- Limit-match.txt - Страница 231
- Pid-owner.txt - Страница 232
- Recent-match.txt - Страница 233
- Sid-owner.txt - Страница 234
- Ttl-inc.txt - Страница 235
- Iptables-save ruleset - Страница 236
- What's next? - Страница 237
- Chapter 15. Graphical User Interfaces for Iptables/netfilter - Страница 238
- fwbuilder - Страница 239
- Turtle Firewall Project - Страница 240
- Integrated Secure Communications System - Страница 241
- IPMenu - Страница 242
- Easy Firewall Generator - Страница 243
- What's next? - Страница 244
- Chapter 16. Commercial products based on Linux, iptables and netfilter - Страница 245
- Ingate Firewall 1200 - Страница 246
- What's next? - Страница 247
- Appendix A. Detailed explanations of special commands - Страница 248
- Listing your active rule-set - Страница 249
- Updating and flushing your tables - Страница 250
- Appendix B. Common problems and questions - Страница 251
- Problems loading modules - Страница 252
- State NEW packets but no SYN bit set - Страница 253
- SYN/ACK and NEW packets - Страница 254
- Internet Service Providers who use assigned IP addresses - Страница 255
- Letting DHCP requests through iptables - Страница 256
- mIRC DCC problems - Страница 257
- Appendix C. ICMP types - Страница 258
- Appendix D. TCP options - Страница 259
- Appendix E. Other resources and links - Страница 260
- Appendix F. Acknowledgments - Страница 264
- Appendix G. History - Страница 265
- Appendix H. GNU Free Documentation License - Страница 267
- 0. PREAMBLE - Страница 268
- 1. APPLICABILITY AND DEFINITIONS - Страница 269
- 2. VERBATIM COPYING - Страница 270
- 3. COPYING IN QUANTITY - Страница 271
- 4. MODIFICATIONS - Страница 272
- 5. COMBINING DOCUMENTS - Страница 274
- 6. COLLECTIONS OF DOCUMENTS - Страница 275
- 7. AGGREGATION WITH INDEPENDENT WORKS - Страница 276
- 8. TRANSLATION - Страница 277
- 9. TERMINATION - Страница 278
- 10. FUTURE REVISIONS OF THIS LICENSE - Страница 279
- How to use this License for your documents - Страница 280
- Appendix I. GNU General Public License - Страница 281
- 0. Preamble - Страница 282
- 1. TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION - Страница 283
- 2. How to Apply These Terms to Your New Programs - Страница 286
- Appendix J. Example scripts code-base - Страница 287
- Example rc.firewall script - Страница 288
- Example rc.DMZ.firewall script - Страница 291
- Example rc.UTIN.firewall script - Страница 294
- Example rc.DHCP.firewall script - Страница 297
- Example rc.flush-iptables script - Страница 300
- Example rc.test-iptables script - Страница 301
- Index - Страница 302
- A - Страница 306
- B - Страница 307
- C - Страница 308
- D - Страница 312
- E - Страница 315
- F - Страница 318
- G - Страница 319
- H - Страница 320
- I - Страница 321
- J - Страница 325
- K - Страница 326
- L - Страница 327
- M - Страница 328
- N - Страница 331
- O - Страница 332
- P - Страница 333
- Q - Страница 335
- R - Страница 336
- S - Страница 339
- T - Страница 347
- U - Страница 352
- V - Страница 354
- W - Страница 355
- X - Страница 356
Starting SNAT and the POSTROUTING chain
So, our final mission would be to get the Network Address Translation up, correct? At least to me. First of all we add a rule to the nat table, in the POSTROUTING chain that will NAT all packets going out on our interface connected to the Internet. For me this would be eth0. However, there are specific variables added to all of the example scripts that may be used to automatically configure these settings. The -t option tells iptables which table to insert the rule in, in this case the nat table. The -A command tells us that we want to Append a new rule to an existing chain named POSTROUTING and -o $INET_IFACE tells us to match all outgoing packets on the INET_IFACE interface (or eth0, per default settings in this script) and finally we set the target to SNAT the packets. So all packets that match this rule will be SNAT'ed to look as if they came from your Internet interface. Do note that you must set which IP address to give outgoing packets with the --to-source option sent to the SNAT target.
In this script we have chosen to use the SNAT target instead of MASQUERADE for a couple of reasons. The first one is that this script was supposed to run on a firewall that has a static IP address. A follow up reason to the first one, would hence be that it is faster and more efficient to use the SNAT target if possible. Of course, it was also used to show how it would work and how it would be used in a real live example. If you do not have a static IP address, you should definitely give thought to use the MASQUERADE target instead which provides a simple and easy facility that will also do NAT for you, but that will automatically grab the IP address that it should use. This takes a little bit extra computing power, but it may most definitely be worth it if you use DHCP for instance. If you would like to have a closer look at how the MASQUERADE target may look, you should look at the rc.DHCP.firewall.txt script.
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