sysctl net.ipv4.icmp_default_ttl

From: Lev V. Vanyan (remedy@mirotel.net)
Date: Tue Jun 11 2002 - 08:33:38 EST


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I wrote a new sysctl flag allowing to control Time To Live for ICMP packages.
I've applied it to my 2.4.18 and it runs stable on fortress.mirotel.net
(Linux i386).

PS: This is my first kernel patch, so it would be better if community will
forgive me in case i've done something wrong :)

- --- linux/net/ipv4/sysctl_net_ipv4.c Wed Oct 31 01:08:12 2001
+++ linux-2.4.18/net/ipv4/sysctl_net_ipv4.c Mon Jun 10 21:51:08 2002
@@ -22,6 +22,7 @@
 extern int sysctl_icmp_echo_ignore_all;
 extern int sysctl_icmp_echo_ignore_broadcasts;
 extern int sysctl_icmp_ignore_bogus_error_responses;
+extern int sysctl_icmp_default_ttl;
 
 /* From ip_fragment.c */
 extern int sysctl_ipfrag_low_thresh;
@@ -176,6 +177,9 @@
         {NET_IPV4_ICMP_IGNORE_BOGUS_ERROR_RESPONSES,
"icmp_ignore_bogus_error_responses",
          &sysctl_icmp_ignore_bogus_error_responses, sizeof(int), 0644, NULL,
          &proc_dointvec},
+ {NET_IPV4_ICMP_DEFAULT_TTL, "icmp_default_ttl",
+ &sysctl_icmp_default_ttl,sizeof(int), 0644,NULL,
+ &proc_dointvec},
         {NET_IPV4_ROUTE, "route", NULL, 0, 0555, ipv4_route_table},
 #ifdef CONFIG_IP_MULTICAST
         {NET_IPV4_IGMP_MAX_MEMBERSHIPS, "igmp_max_memberships",
- --- linux/net/ipv4/ip_output.c Thu Oct 18 00:16:39 2001
+++ linux-2.4.18/net/ipv4/ip_output.c Tue Jun 11 15:58:07 2002
@@ -84,6 +84,9 @@
 
 int sysctl_ip_dynaddr = 0;
 int sysctl_ip_default_ttl = IPDEFTTL;
+#ifdef CONFIG_SYSCTL
+extern int sysctl_icmp_default_ttl;
+#endif
 
 /* Generate a checksum for an outgoing IP datagram. */
 __inline__ void ip_send_check(struct iphdr *iph)
@@ -572,10 +575,17 @@
                                  */
                                 mf = htons(IP_MF);
                         }
- - if (rt->rt_type == RTN_MULTICAST)
- - iph->ttl = sk->protinfo.af_inet.mc_ttl;
- - else
- - iph->ttl = sk->protinfo.af_inet.ttl;
+#ifdef CONFIG_SYSCTL
+ if(sk->protocol != IPPROTO_ICMP) {
+#endif
+ if (rt->rt_type == RTN_MULTICAST)
+ iph->ttl = sk->protinfo.af_inet.mc_ttl;
+ else
+ iph->ttl = sk->protinfo.af_inet.ttl;
+#ifdef CONFIG_SYSCTL
+ }
+ else iph->ttl = sysctl_icmp_default_ttl;
+#endif
                         iph->protocol = sk->protocol;
                         iph->check = 0;
                         iph->saddr = rt->rt_src;
@@ -693,10 +703,19 @@
                 iph->tos=sk->protinfo.af_inet.tos;
                 iph->tot_len = htons(length);
                 iph->frag_off = df;
- - iph->ttl=sk->protinfo.af_inet.mc_ttl;
+ /* set TTL for ICMP packets */
+#ifdef CONFIG_SYSCTL
+ if(iph->protocol == IPPROTO_ICMP)
+ iph->ttl = sysctl_icmp_default_ttl;
+ else {
+#endif
+ if(rt->rt_type != RTN_MULTICAST)
+ iph->ttl = sk->protinfo.af_inet.ttl;
+ else iph->ttl = sk->protinfo.af_inet.mc_ttl;
+#ifdef CONFIG_SYSCTL
+ }
+#endif
                 ip_select_ident(iph, &rt->u.dst, sk);
- - if (rt->rt_type != RTN_MULTICAST)
- - iph->ttl=sk->protinfo.af_inet.ttl;
                 iph->protocol=sk->protocol;
                 iph->saddr=rt->rt_src;
                 iph->daddr=rt->rt_dst;
- --- linux/net/ipv4/icmp.c Mon Feb 25 21:38:14 2002
+++ linux-2.4.18/net/ipv4/icmp.c Tue Jun 11 15:36:36 2002
@@ -143,6 +143,9 @@
 int sysctl_icmp_echo_ignore_all;
 int sysctl_icmp_echo_ignore_broadcasts;
 
+/* Control max icmp ttl. */
+int sysctl_icmp_default_ttl = 255;
+
 /* Control parameter - ignore bogus broadcast responses? */
 int sysctl_icmp_ignore_bogus_error_responses;
 
ð

- --
Lev V. Vanyan Software Engineer
Mirotel ISP nic-hdl: VL1580-RIPE, LV2560-NIC
mailto: remedy@mirotel.net
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This archive was generated by hypermail 2b29 : Sat Jun 15 2002 - 22:00:22 EST