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The attached patch (against 2.4.4-ac10) adds the
/proc/sys/net/ipv4/conf/*/hidden option which is present in 2.2.x series.
This is somewhat similar to the arp-filter functionality which was added in
~2.4.4-ac10. The difference is that this is not dependent upon the routing
table, it is simply configured using proc fs.

This is particularly useful in load-balanced server farms where loopback
addresses are configured for direct client-server traffic. Without this
patch, Linux will respond to arp requests for the virtual IPs, making
effective load balancing difficult.

-Phil Oester


diff -r -u -x *~ -x *.rej
linux-2.4.4-ac10/Documentation/filesystems/proc.txt
linux-2.4.4-ac10-hidden/Documentation/filesystems/proc.txt
--- linux-2.4.4-ac10/Documentation/filesystems/proc.txt Fri Apr 6 13:42:48
2001
+++ linux-2.4.4-ac10-hidden/Documentation/filesystems/proc.txt Thu May 17
15:01:45 2001
@@ -1578,6 +1578,17 @@

Determines whether to send ICMP redirects to other hosts.

+hidden
+------
+
+Hide addresses attached to this device from other devices.
+Such addresses will never be selected by source address autoselection
+mechanism. Also, host will not answer broadcast ARP requests for them and
+will not announce it as source address of ARP requests. The addresses are,
+however, still reachable via IP. This is primarily useful in
load-balancing
+environments. This flag is activated only if it is enabled both in
specific
+device section and in "all" section.
+
Routing settings
----------------

diff -r -u -x *~ -x *.rej
linux-2.4.4-ac10/Documentation/networking/ip-sysctl.txt
linux-2.4.4-ac10-hidden/Documentation/networking/ip-sysctl.txt
--- linux-2.4.4-ac10/Documentation/networking/ip-sysctl.txt Thu May 17
14:53:02 2001
+++ linux-2.4.4-ac10-hidden/Documentation/networking/ip-sysctl.txt Thu May
17 15:02:47 2001
@@ -392,6 +392,15 @@
Default value is 0. Note that some distributions enable it
in startip scripts.

+hidden - BOOLEAN
+ Hide addresses attached to this device from other devices.
+ Such addresses will never be selected by source address autoselection
+ mechanism. Also, host will not answer broadcast ARP requests for them and
+ will not announce it as source address of ARP requests. The addresses
are,
+ however, still reachable via IP. This is primarily useful in
load-balancing
+ environments. This flag is activated only if it is enabled both in
specific
+ device section and in "all" section.
+
Alexey Kuznetsov.
kuznet@ms2.inr.ac.ru

diff -r -u -x *~ -x *.rej linux-2.4.4-ac10/include/linux/inetdevice.h
linux-2.4.4-ac10-hidden/include/linux/inetdevice.h
--- linux-2.4.4-ac10/include/linux/inetdevice.h Thu May 17 14:53:07 2001
+++ linux-2.4.4-ac10-hidden/include/linux/inetdevice.h Thu May 17 14:30:25
2001
@@ -18,6 +18,7 @@
int mc_forwarding;
int tag;
int arp_filter;
+ int hidden;
void *sysctl;
};

@@ -44,6 +45,7 @@

#define IN_DEV_LOG_MARTIANS(in_dev) (ipv4_devconf.log_martians ||
(in_dev)->cnf.log_martians)
#define IN_DEV_PROXY_ARP(in_dev) (ipv4_devconf.proxy_arp ||
(in_dev)->cnf.proxy_arp)
+#define IN_DEV_HIDDEN(in_dev) ((in_dev)->cnf.hidden &&
ipv4_devconf.hidden)
#define IN_DEV_SHARED_MEDIA(in_dev) (ipv4_devconf.shared_media ||
(in_dev)->cnf.shared_media)
#define IN_DEV_TX_REDIRECTS(in_dev) (ipv4_devconf.send_redirects ||
(in_dev)->cnf.send_redirects)
#define IN_DEV_SEC_REDIRECTS(in_dev) (ipv4_devconf.secure_redirects ||
(in_dev)->cnf.secure_redirects)
diff -r -u -x *~ -x *.rej linux-2.4.4-ac10/include/linux/sysctl.h
linux-2.4.4-ac10-hidden/include/linux/sysctl.h
--- linux-2.4.4-ac10/include/linux/sysctl.h Thu May 17 14:53:07 2001
+++ linux-2.4.4-ac10-hidden/include/linux/sysctl.h Thu May 17 14:32:40 2001
@@ -326,7 +326,8 @@
NET_IPV4_CONF_BOOTP_RELAY=10,
NET_IPV4_CONF_LOG_MARTIANS=11,
NET_IPV4_CONF_TAG=12,
- NET_IPV4_CONF_ARPFILTER=13
+ NET_IPV4_CONF_ARPFILTER=13,
+ NET_IPV4_CONF_HIDDEN=14
};

/* /proc/sys/net/ipv6 */
diff -r -u -x *~ -x *.rej linux-2.4.4-ac10/net/ipv4/arp.c
linux-2.4.4-ac10-hidden/net/ipv4/arp.c
--- linux-2.4.4-ac10/net/ipv4/arp.c Thu May 17 14:53:07 2001
+++ linux-2.4.4-ac10-hidden/net/ipv4/arp.c Thu May 17 14:47:44 2001
@@ -66,7 +66,9 @@
* Alexey Kuznetsov: new arp state machine;
* now it is in net/core/neighbour.c.
* Krzysztof Halasa: Added Frame Relay ARP support.
- */
+ * Julian Anastasov: "hidden" flag: hide the
+ * interface and don't reply for it
+*/

#include <linux/types.h>
#include <linux/string.h>
@@ -317,12 +319,23 @@
static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
{
u32 saddr;
+ int from_skb;
+ struct in_device *in_dev2 = NULL;
+ struct net_device *dev2 = NULL;
u8 *dst_ha = NULL;
struct net_device *dev = neigh->dev;
u32 target = *(u32*)neigh->primary_key;
int probes = atomic_read(&neigh->probes);

- if (skb && inet_addr_type(skb->nh.iph->saddr) == RTN_LOCAL)
+ from_skb = (skb &&
+ (dev2 = ip_dev_find(skb->nh.iph->saddr)) != NULL &&
+ (in_dev2 = in_dev_get(dev2)) != NULL &&
+ !IN_DEV_HIDDEN(in_dev2));
+ if (dev2) {
+ if (in_dev2) in_dev_put(in_dev2);
+ dev_put(dev2);
+ }
+ if (from_skb)
saddr = skb->nh.iph->saddr;
else
saddr = inet_select_addr(dev, target, RT_SCOPE_LINK);
@@ -742,9 +755,22 @@

/* Special case: IPv4 duplicate address detection packet (RFC2131) */
if (sip == 0) {
- if (arp->ar_op == __constant_htons(ARPOP_REQUEST) &&
- inet_addr_type(tip) == RTN_LOCAL)
+ int reply;
+ struct net_device *dev2 = NULL;
+ struct in_device *in_dev2 = NULL;
+
+ reply =
+ (arp->ar_op == __constant_htons(ARPOP_REQUEST) &&
+ (dev2 = ip_dev_find(tip)) != NULL &&
+ (dev2 == dev ||
+ ((in_dev2 = in_dev_get(dev2)) != NULL &&
+ !IN_DEV_HIDDEN(in_dev2))));
+ if (dev2) {
+ if (in_dev2) in_dev_put(in_dev2);
+ dev_put(dev2);
+ if (reply)

arp_send(ARPOP_REPLY,ETH_P_ARP,tip,dev,tip,sha,dev->dev_addr,dev->dev_addr);
+ }
goto out;
}

@@ -760,10 +786,29 @@
int dont_send = 0;
if (IN_DEV_ARPFILTER(in_dev))
dont_send |= arp_filter(sip,tip,dev);
- if (!dont_send)
+ if (!dont_send) {
+ if (ipv4_devconf.hidden && skb->pkt_type != PACKET_HOST) {
+ int skip;
+ struct net_device *dev2 = NULL;
+ struct in_device *in_dev2 = NULL;
+
+ skip =
+ ((dev2 = ip_dev_find(tip)) != NULL &&
+ dev2 != dev &&
+ (in_dev2=in_dev_get(dev2)) != NULL &&
+ IN_DEV_HIDDEN(in_dev2));
+ if (dev2) {
+ if (in_dev2) in_dev_put(in_dev2);
+ dev_put(dev2);
+ if (skip) {
+ neigh_release(n);
+ goto out;
+ }
+ }
+ }
arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
-
- neigh_release(n);
+ neigh_release(n);
+ }
}
goto out;
} else if (IN_DEV_FORWARD(in_dev)) {
diff -r -u -x *~ -x *.rej linux-2.4.4-ac10/net/ipv4/devinet.c
linux-2.4.4-ac10-hidden/net/ipv4/devinet.c
--- linux-2.4.4-ac10/net/ipv4/devinet.c Thu May 17 14:53:07 2001
+++ linux-2.4.4-ac10-hidden/net/ipv4/devinet.c Thu May 17 14:51:44 2001
@@ -736,7 +736,8 @@

read_lock(&in_dev->lock);
for_primary_ifa(in_dev) {
- if (ifa->ifa_scope != RT_SCOPE_LINK &&
+ if (!IN_DEV_HIDDEN(in_dev) &&
+ ifa->ifa_scope != RT_SCOPE_LINK &&
ifa->ifa_scope <= scope) {
read_unlock(&in_dev->lock);
read_unlock(&inetdev_lock);
@@ -1016,7 +1017,7 @@
static struct devinet_sysctl_table
{
struct ctl_table_header *sysctl_header;
- ctl_table devinet_vars[14];
+ ctl_table devinet_vars[15];
ctl_table devinet_dev[2];
ctl_table devinet_conf_dir[2];
ctl_table devinet_proto_dir[2];
@@ -1061,6 +1062,9 @@
&proc_dointvec},
{NET_IPV4_CONF_ARPFILTER, "arp_filter",
&ipv4_devconf.arp_filter, sizeof(int), 0644, NULL,
+ &proc_dointvec},
+ {NET_IPV4_CONF_HIDDEN, "hidden",
+ &ipv4_devconf.hidden, sizeof(int), 0644, NULL,
&proc_dointvec},
{0}},

-
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