FreeBSD eats 169.254.x.x addressed packets

Guy Helmer ghelmer at palisadesystems.com
Tue Jun 8 18:47:29 UTC 2010


On Jun 8, 2010, at 12:45 PM, Stephen Clark wrote:

> Hi,
> 
> Why does FreeBSD 6.3 eat 169.254.x.x addressed packet when
> 4.9 didn't?
> 
> ***** 6.3 *****
> $ sudo ipfstat -nio
> empty list for ipfilter(out)
> empty list for ipfilter(in)
> Z2984:~
> $ ifconfig rl0
> rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>        options=8<VLAN_MTU>
>        inet 192.168.129.1 netmask 0xffffff00 broadcast 192.168.129.255
>        inet 169.254.1.1 netmask 0xffff0000 broadcast 169.254.255.255
>        ether 00:30:18:ae:7c:77
>        media: Ethernet autoselect (100baseTX <full-duplex>)
>        status: active
> Z2984:~
> $ ping 169.254.1.1
> PING 169.254.1.1 (169.254.1.1): 56 data bytes
> ^C
> --- 169.254.1.1 ping statistics ---
> 4 packets transmitted, 0 packets received, 100% packet loss
> Z2984:~
> $ uname -a
> FreeBSD Z2984.netwolves.com 6.3-RELEASE-p15 FreeBSD 6.3-RELEASE-p15 #17: Fri Apr 16 12:51:57 EST 2010
> 
> **** 4.9 *****
> FreeBSD H101494.com 4.9-STABLE FreeBSD 4.9-STABLE #59: Thu Mar 30 13:42:10 EST 2006     root at A1234.com:/mnt2/src/sys/compile/  i386
> H101494# ipf -Fa
> H101494# ipfstat -nio
> empty list for ipfilter(out)
> empty list for ipfilter(in)
> H101494# ifconfig rl0
> rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>        inet 10.254.151.1 netmask 0xffffff00 broadcast 10.254.151.255
>        inet 10.255.3.30 netmask 0xffffffff broadcast 10.255.3.30
>        inet 10.255.4.30 netmask 0xffffffff broadcast 10.255.4.30
>        inet 169.254.202.1 netmask 0xffff0000 broadcast 169.254.255.255
>        ether 00:30:18:a3:49:b5
>        media: Ethernet autoselect (none)
>        status: no carrier
> H101494# ping 169.254.202.1
> PING 169.254.202.1 (169.254.202.1): 56 data bytes
> 64 bytes from 169.254.202.1: icmp_seq=0 ttl=64 time=0.052 ms
> 64 bytes from 169.254.202.1: icmp_seq=1 ttl=64 time=0.080 ms
> 64 bytes from 169.254.202.1: icmp_seq=2 ttl=64 time=0.081 ms
> ^C
> --- 169.254.202.1 ping statistics ---
> 3 packets transmitted, 3 packets received, 0% packet loss
> round-trip min/avg/max/stddev = 0.052/0.071/0.081/0.013 ms
> 
> 


That was a feature added to sys/netinet/in.c and ip_input.c back in 2007 to obey RFC 3927 not to output datagrams destined for 169.254.0.0/16.

On a system that needed to be able to send datagrams to 169.254.0.0/16 addresses, I wrote this patch to add a sysctl knob net.inet.fwd_link_local to dynamically allow a system to send those datagrams: 


Index: in.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/in.c,v
retrieving revision 1.102.2.4.2.1
diff -u -r1.102.2.4.2.1 in.c
--- in.c	15 Apr 2009 03:14:26 -0000	1.102.2.4.2.1
+++ in.c	29 Jul 2009 15:10:42 -0000
@@ -67,6 +67,9 @@
 	    struct in_ifaddr *, struct sockaddr_in *, int);
 static void	in_purgemaddrs(struct ifnet *);
 
+int ip_fwdlinklocal = 0;
+SYSCTL_INT(_net_inet_ip, OID_AUTO, fwd_link_local, CTLFLAG_RW,
+	&ip_fwdlinklocal, 0, "Forward link-local addresses");
 static int subnetsarelocal = 0;
 SYSCTL_INT(_net_inet_ip, OID_AUTO, subnets_are_local, CTLFLAG_RW,
 	&subnetsarelocal, 0, "Treat all subnets as directly connected");
@@ -129,7 +132,8 @@
 	register u_long i = ntohl(in.s_addr);
 	register u_long net;
 
-	if (IN_EXPERIMENTAL(i) || IN_MULTICAST(i) || IN_LINKLOCAL(i))
+	if (IN_EXPERIMENTAL(i) || IN_MULTICAST(i) ||
+	    (!ip_fwdlinklocal && IN_LINKLOCAL(i)))
 		return (0);
 	if (IN_CLASSA(i)) {
 		net = i & IN_CLASSA_NET;
Index: ip_input.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/ip_input.c,v
retrieving revision 1.332.2.5.2.1
diff -u -r1.332.2.5.2.1 ip_input.c
--- ip_input.c	15 Apr 2009 03:14:26 -0000	1.332.2.5.2.1
+++ ip_input.c	29 Jul 2009 15:10:44 -0000
@@ -134,6 +134,7 @@
 static struct	ifqueue ipintrq;
 static int	ipqmaxlen = IFQ_MAXLEN;
 
+extern	int ip_fwdlinklocal;
 extern	struct domain inetdomain;
 extern	struct protosw inetsw[];
 u_char	ip_protox[IPPROTO_MAX];
@@ -532,7 +533,7 @@
 		}
 	}
 	/* RFC 3927 2.7: Do not forward datagrams for 169.254.0.0/16. */
-	if (IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr))) {
+	if (!ip_fwdlinklocal && IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr))) {
 		ipstat.ips_cantforward++;
 		m_freem(m);
 		return;




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