FreeBSD eats 169.254.x.x addressed packets

Tue Jun 8 18:41:10 UTC 2010

On Jun 8, 2010, at 1:30 PM, Stephen Clark wrote:

> On 06/08/2010 02:21 PM, Guy Helmer wrote:
>> 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;
>> 
>> 
> Hmmm... how is not responding to pings associated with forwarding?
> 

My previous understanding was that RFC 3927 did not allow transmitting datagrams involving the 169.254.0.0/16 link-local prefix; now that I've looked over the RFC more closely, I'm not sure that is the case.

I have cc'ed Bruce Simpson on this message in hopes that he can shed some light on this.  I believe he committed the change that disallowed transmitting from 169.254.0.0/16 addresses.

Guy