Re: Funny problem

[Ralph Metzler <rjkm@netcologne.de>]

Ivo Simicevic writes:
 > On Fri, Feb 18, 2000 at 01:43:42PM +0100, Ivo Simicevic wrote:
 > > I have correctly connected to EON by using Cyberlogin.
 > > If i try to ping proxy I can see that it's return 
 > > packets are arriving (by monitoring with tcpdump on dvb0
 > > interface) but ping doesn't get these packets so I
 > > have 100% lost statistics.
 > > 
 > > Any reason why kernel would discard those packets and
 > > not use it?
 > > 
 > > Regards,
 > > 
 > > Ivo.
 > > 
 > 
 > Just solved it ?!
 > 
 > If someone else has the same problem use
 > 
 > echo "0" >/proc/sys/net/ipv4/conf/dvb0/rp_filter 
 > 
 > 
 > I would like to know why this solves problem, though.

>From linux/Documentation/networking/ip-sysctl.txt:


rp_filter - INTEGER
	2 - do source validation by reversed path, as specified in RFC1812
	    Recommended option for single homed hosts and stub network
	    routers. Could cause troubles for complicated (not loop free)
	    networks running a slow unreliable protocol (sort of RIP),
	    or using static routes.

	1 - (DEFAULT) Weaker form of RP filtering: drop all the packets
	    that look as sourced at a directly connected interface, but
	    were input from another interface.
	    
	0 - No source validation. 

	NOTE: do not disable this option! All BSD derived routing software
	(sort of gated, routed etc. etc.) is confused by such packets,
	even if they are valid. When enabled it also prevents ip spoofing
	in some limited fashion.

	NOTE: this option is turned on per default only when ip_forwarding
	is on. For non-forwarding hosts it doesn't make much sense and 
	makes some legal multihoming configurations impossible.



Since the EON proxy sends the packets to the interface with the
internet connection (ISDN, PPP, ...) but they arrive through the dvb0
device the filter does not let them through.
So, you should check if your configuration enables this.
README.sb1000 in the same directory states the same problem for a
one-way cable modem.

Ralph