Re: [patch] Fix SNMPv2 ipOutNoRoutes counter error

[David Miller]

From: weidong [EMAIL PROTECTED]
Date: Tue, 05 Dec 2006 11:49:46 -0500

 Hi All:
 When I tested linux kernel 2.6.18.3, and find that kernel statistics
 about IPSTATS_MIB_OUTNOROUTES which exsits in file /proc/net/snmp
 doesn't increase correctly.  The criteria conform to RFC2011:
 
   ipOutNoRoutes OBJECT-TYPE
 SYNTAX  Counter32
 MAX-ACCESS  read-only
 STATUS  current
 DESCRIPTION
 The number of IP datagrams discarded because no route could
 be found to transmit them to their destination.  Note that
 this counter includes any packets counted in ipForwDatagrams
 which meet this `no-route' criterion.  Note that this
 includes any datagrams which a host cannot route because all
 of its default routers are down.
 ::= { ip 12 }
 
 When a host received an IP packet, but the destination address is not
 this host. The kernel just discards the IP packet but with no increment
 for this counter.
 
 When a router received an IP packet that this router can't forward due
 to no route found. Kernel just simply invoke ip_error(), and send ICMP
 packet. Also do nothing for this counter.
 
 Signed-off-by: Wei Dong [EMAIL PROTECTED]

Hosts which have forwarding disabled, are not forwarding and
therefore not routing in the sense being described here.

So bumping this counter when the ip_forward sysctl is 0 makes
no sense.

We are not even getting to the output path when the route lookup
fails in ip_rcv_finish().  This means this silly SNMP output route
failed counter will get bumped like crazy when promiscuous mode is
enabled on an interface, and that makes zero sense.

This patch, at least in it's current form, is not correct.
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[patch] Fix SNMPv2 ipOutNoRoutes counter error

[weidong]

Hi All:
When I tested linux kernel 2.6.18.3, and find that kernel statistics
about IPSTATS_MIB_OUTNOROUTES which exsits in file /proc/net/snmp
doesn't increase correctly.  The criteria conform to RFC2011:

  ipOutNoRoutes OBJECT-TYPE
SYNTAX  Counter32
MAX-ACCESS  read-only
STATUS  current
DESCRIPTION
The number of IP datagrams discarded because no route could
be found to transmit them to their destination.  Note that
this counter includes any packets counted in ipForwDatagrams
which meet this `no-route' criterion.  Note that this
includes any datagrams which a host cannot route because all
of its default routers are down.
::= { ip 12 }

When a host received an IP packet, but the destination address is not
this host. The kernel just discards the IP packet but with no increment
for this counter.

When a router received an IP packet that this router can't forward due
to no route found. Kernel just simply invoke ip_error(), and send ICMP
packet. Also do nothing for this counter.

Signed-off-by: Wei Dong [EMAIL PROTECTED]

diff -ruN old/net/ipv4/icmp.c new/net/ipv4/icmp.c
--- old/net/ipv4/icmp.c 2006-09-20 00:42:06.0 -0300
+++ new/net/ipv4/icmp.c 2006-12-04 11:46:39.0 -0300
@@ -580,6 +580,9 @@
icmp_param.data_len = room;
icmp_param.head_len = sizeof(struct icmphdr);
 
+   if (code == ICMP_NET_UNREACH)
+   IP_INC_STATS_BH(IPSTATS_MIB_OUTNOROUTES);
+
icmp_push_reply(icmp_param, ipc, rt);
 ende:
ip_rt_put(rt);
diff -ruN old/net/ipv4/ip_input.c new/net/ipv4/ip_input.c
--- old/net/ipv4/ip_input.c 2006-09-20 00:42:06.0 -0300
+++ new/net/ipv4/ip_input.c 2006-11-29 11:15:52.0 -0300
@@ -340,8 +340,10 @@
int err = ip_route_input(skb, iph-daddr, iph-saddr, iph-tos,
 skb-dev);
if (unlikely(err)) {
-   if (err == -EHOSTUNREACH)
+   if (err == -EHOSTUNREACH) {
IP_INC_STATS_BH(IPSTATS_MIB_INADDRERRORS);
+   IP_INC_STATS_BH(IPSTATS_MIB_OUTNOROUTES);
+   }
goto drop; 
}
}


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