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
LOG target options
The LOG target is specially designed for logging detailed information about packets. These could, for example, be considered as illegal. Or, logging can be used purely for bug hunting and error finding. The LOG target will return specific information on packets, such as most of the IP headers and other information considered interesting. It does this via the kernel logging facility, normally syslogd. This information may then be read directly with dmesg, or from the syslogd logs, or with other programs or applications. This is an excellent target to use to debug your rule-sets, so that you can see what packets go where and what rules are applied on what packets. Note as well that it could be a really great idea to use the LOG target instead of the DROP target while you are testing a rule you are not 100% sure about on a production firewall, since a syntax error in the rule-sets could otherwise cause severe connectivity problems for your users. Also note that the ULOG target may be interesting if you are using really extensive logging, since the ULOG target has support for direct logging to MySQL databases and suchlike.
Note that if you get undesired logging direct to consoles, this is not an iptables or Netfilter problem, but rather a problem caused by your syslogd configuration - most probably /etc/syslog.conf. Read more in man syslog.conf for information about this kind of problem.
You may also need to tweak your dmesg settings. dmesg is the command that changes which errors from the kernel that should be shown on the console. dmesg -n 1 should prevent all messages from showing up on the console, except panic messages. The dmesg message levels matches exactly the syslogd levels, and it only works on log messages from the kernel facility. For more information, see man dmesg.
The LOG target currently takes five options that could be of interest if you have specific information needs, or want to set different options to specific values. They are all listed below.
Table 11-8. LOG target options
Option | --log-level |
Example | iptables -A FORWARD -p tcp -j LOG --log-level debug |
Explanation | This is the option to tell iptables and syslog which log level to use. For a complete list of log levels read the syslog.conf manual. Normally there are the following log levels, or priorities as they are normally referred to: debug, info, notice, warning, warn, err, error, crit, alert, emerg and panic. The keyword error is the same as err, warn is the same as warning and panic is the same as emerg. Note that all three of these are deprecated, in other words do not use error, warn and panic. The priority defines the severity of the message being logged. All messages are logged through the kernel facility. In other words, setting kern.=info /var/log/iptables in your syslog.conf file and then letting all your LOG messages in iptables use log level info, would make all messages appear in the /var/log/iptables file. Note that there may be other messages here as well from other parts of the kernel that uses the info priority. For more information on logging I recommend you to read the syslog and syslog.conf man-pages as well as other HOWTOs etc. |
Option | --log-prefix |
Example | iptables -A INPUT -p tcp -j LOG --log-prefix "INPUT packets" |
Explanation | This option tells iptables to prefix all log messages with a specific prefix, which can then easily be combined with grep or other tools to track specific problems and output from different rules. The prefix may be up to 29 letters long, including white-spaces and other special symbols. |
Option | --log-tcp-sequence |
Example | iptables -A INPUT -p tcp -j LOG --log-tcp-sequence |
Explanation | This option will log the TCP Sequence numbers, together with the log message. The TCP Sequence numbers are special numbers that identify each packet and where it fits into a TCP sequence, as well as how the stream should be reassembled. Note that this option constitutes a security risk if the logs are readable by unauthorized users, or by the world for that matter. As does any log that contains output from iptables. |
Option | --log-tcp-options |
Example | iptables -A FORWARD -p tcp -j LOG --log-tcp-options |
Explanation | The --log-tcp-options option logs the different options from the TCP packet headers and can be valuable when trying to debug what could go wrong, or what has actually gone wrong. This option does not take any variable fields or anything like that, just as most of the LOG options don't. |
Option | --log-ip-options |
Example | iptables -A FORWARD -p tcp -j LOG --log-ip-options |
Explanation | The --log-ip-options option will log most of the IP packet header options. This works exactly the same as the --log-tcp-options option, but instead works on the IP options. These logging messages may be valuable when trying to debug or track specific culprits, as well as for debugging - in just the same way as the previous option. |
Note Works under Linux kernel 2.3, 2.4, 2.5 and 2.6.
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