2.2.6 breaks one-way cable modem (sb1000)

Illuminatus Primus (vermont@gate.net)
Sat, 24 Apr 1999 18:16:50 -0400

After upgrading from 2.2.0 to 2.2.6, it seems that packets that arrive
on an interface using the same address as another previously-existing
interface get discarded.

For example, using the Surfboard 1000 driver
(http://www.jacksonville.net/~fventuri/sb1000-1.1.2.tar.gz),
and connecting to MediaOne, my cable provider, results in ppp0 & cm0
interfaces:

ppp0 Link encap:Point-to-Point Protocol
inet addr:24.129.30.142 P-t-P:24.129.43.75 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:39 errors:0 dropped:0 overruns:0 frame:0
TX packets:2103 errors:0 dropped:0 overruns:0 carrier:0
Collisions:0

cm0 Link encap:Ethernet HWaddr 00:00:30:B7:03:37
inet addr:24.129.30.142 P-t-P:24.129.43.75 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MTU:0 Metric:1
RX packets:2020 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
Collisions:0
Interrupt:11 Base address:0x1e0

This seems to work without any problems in 2.2.0; packets go out
through the ppp0 interface, and packets come in through the cm0
interface (except when the cable modem overheats!).

However, in 2.2.6, I see the cm0 RX packet count increasing in sync
with pings that I send out, yet none of those packets are seen by ping
itself. I can also see the raw packets arriving via tcpdump of the
cm0 interface.

How do I correct this problem? What is it caused by?

Any help would be appreciated!

Thanks,
Vermont
(please CC me at <vermont@gate.net>, since I'm not subscribed to
linux-kernel)

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