summaryrefslogtreecommitdiffstats
path: root/extensions
diff options
context:
space:
mode:
authorArnaud Ebalard <arno@natisbad.org>2007-01-16 14:19:20 +0000
committerPatrick McHardy <kaber@trash.net>2007-01-16 14:19:20 +0000
commite4076172c33810472d9d658554588b6e379a4fbe (patch)
tree971ebca828b5dea3231025c39fe5ebd9862b0a79 /extensions
parent9561606bd938ed4b2614716a08a2856d4ef5e995 (diff)
Add ip6tables TCPMSS extension (Arnaud Ebalard <arno@natisbad.org>)
Kernel part will go in 2.6.21.
Diffstat (limited to 'extensions')
-rw-r--r--extensions/libip6t_TCPMSS.c134
-rw-r--r--extensions/libip6t_TCPMSS.man42
2 files changed, 176 insertions, 0 deletions
diff --git a/extensions/libip6t_TCPMSS.c b/extensions/libip6t_TCPMSS.c
new file mode 100644
index 00000000..7fcccd5c
--- /dev/null
+++ b/extensions/libip6t_TCPMSS.c
@@ -0,0 +1,134 @@
+/* Shared library add-on to iptables to add TCPMSS target support.
+ *
+ * Copyright (c) 2000 Marc Boucher
+*/
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <getopt.h>
+
+#include <ip6tables.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter_ipv6/ip6t_TCPMSS.h>
+
+struct mssinfo {
+ struct ip6t_entry_target t;
+ struct ip6t_tcpmss_info mss;
+};
+
+/* Function which prints out usage message. */
+static void
+help(void)
+{
+ printf(
+"TCPMSS target v%s mutually-exclusive options:\n"
+" --set-mss value explicitly set MSS option to specified value\n"
+" --clamp-mss-to-pmtu automatically clamp MSS value to (path_MTU - 60)\n",
+IPTABLES_VERSION);
+}
+
+static struct option opts[] = {
+ { "set-mss", 1, 0, '1' },
+ { "clamp-mss-to-pmtu", 0, 0, '2' },
+ { 0 }
+};
+
+/* Initialize the target. */
+static void
+init(struct ip6t_entry_target *t, unsigned int *nfcache)
+{
+}
+
+/* Function which parses command options; returns true if it
+ ate an option */
+static int
+parse(int c, char **argv, int invert, unsigned int *flags,
+ const struct ip6t_entry *entry,
+ struct ip6t_entry_target **target)
+{
+ struct ip6t_tcpmss_info *mssinfo
+ = (struct ip6t_tcpmss_info *)(*target)->data;
+
+ switch (c) {
+ unsigned int mssval;
+
+ case '1':
+ if (*flags)
+ exit_error(PARAMETER_PROBLEM,
+ "TCPMSS target: Only one option may be specified");
+ if (string_to_number(optarg, 0, 65535 - 60, &mssval) == -1)
+ exit_error(PARAMETER_PROBLEM, "Bad TCPMSS value `%s'", optarg);
+
+ mssinfo->mss = mssval;
+ *flags = 1;
+ break;
+
+ case '2':
+ if (*flags)
+ exit_error(PARAMETER_PROBLEM,
+ "TCPMSS target: Only one option may be specified");
+ mssinfo->mss = IP6T_TCPMSS_CLAMP_PMTU;
+ *flags = 1;
+ break;
+
+ default:
+ return 0;
+ }
+
+ return 1;
+}
+
+static void
+final_check(unsigned int flags)
+{
+ if (!flags)
+ exit_error(PARAMETER_PROBLEM,
+ "TCPMSS target: At least one parameter is required");
+}
+
+/* Prints out the targinfo. */
+static void
+print(const struct ip6t_ip6 *ip6,
+ const struct ip6t_entry_target *target,
+ int numeric)
+{
+ const struct ip6t_tcpmss_info *mssinfo =
+ (const struct ip6t_tcpmss_info *)target->data;
+ if(mssinfo->mss == IP6T_TCPMSS_CLAMP_PMTU)
+ printf("TCPMSS clamp to PMTU ");
+ else
+ printf("TCPMSS set %u ", mssinfo->mss);
+}
+
+/* Saves the union ip6t_targinfo in parsable form to stdout. */
+static void
+save(const struct ip6t_ip6 *ip, const struct ip6t_entry_target *target)
+{
+ const struct ip6t_tcpmss_info *mssinfo =
+ (const struct ip6t_tcpmss_info *)target->data;
+
+ if(mssinfo->mss == IP6T_TCPMSS_CLAMP_PMTU)
+ printf("--clamp-mss-to-pmtu ");
+ else
+ printf("--set-mss %u ", mssinfo->mss);
+}
+
+static struct ip6tables_target mss = {
+ .next = NULL,
+ .name = "TCPMSS",
+ .version = IPTABLES_VERSION,
+ .size = IP6T_ALIGN(sizeof(struct ip6t_tcpmss_info)),
+ .userspacesize = IP6T_ALIGN(sizeof(struct ip6t_tcpmss_info)),
+ .help = &help,
+ .init = &init,
+ .parse = &parse,
+ .final_check = &final_check,
+ .print = &print,
+ .save = &save,
+ .extra_opts = opts
+};
+
+void _init(void)
+{
+ register_target6(&mss);
+}
diff --git a/extensions/libip6t_TCPMSS.man b/extensions/libip6t_TCPMSS.man
new file mode 100644
index 00000000..b4c357e8
--- /dev/null
+++ b/extensions/libip6t_TCPMSS.man
@@ -0,0 +1,42 @@
+This target allows to alter the MSS value of TCP SYN packets, to control
+the maximum size for that connection (usually limiting it to your
+outgoing interface's MTU minus 60). Of course, it can only be used
+in conjunction with
+.BR "-p tcp" .
+It is only valid in the
+.BR mangle
+table.
+.br
+This target is used to overcome criminally braindead ISPs or servers
+which block ICMPv6 Packet Too Big packets or are unable to send them.
+The symptoms of this problem are that everything works fine from your
+Linux firewall/router, but machines behind it can never exchange large
+packets:
+.PD 0
+.RS 0.1i
+.TP 0.3i
+1)
+Web browsers connect, then hang with no data received.
+.TP
+2)
+Small mail works fine, but large emails hang.
+.TP
+3)
+ssh works fine, but scp hangs after initial handshaking.
+.RE
+.PD
+Workaround: activate this option and add a rule to your firewall
+configuration like:
+.nf
+ ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \\
+ -j TCPMSS --clamp-mss-to-pmtu
+.fi
+.TP
+.BI "--set-mss " "value"
+Explicitly set MSS option to specified value.
+.TP
+.B "--clamp-mss-to-pmtu"
+Automatically clamp MSS value to (path_MTU - 60).
+.TP
+These options are mutually exclusive.
+