Bug related to bridge & PPP

Zoltan Hidvegi (hzoli@cs.elte.hu)
Wed, 20 Nov 1996 02:54:04 +0100 (MET)

I recently tried the linux ethernet bridge code. It worked perfectly but I
encountered one problem. The machine which I used as a bidge was a normal
server, with two modems for PPP dial-in. But when the bridge code was
enabled, the ppp client and the server was unable to communicate with each
other. But surprisingly the machine correctly forwared each IP packet so
every other site was usable from the client exept the ppp server itself.
As soon as brcfg -dis command was issued the server started seeing the
client but and other brcfg -ena broke the connection again (but forwarding
still worked).

It was not even necessary to have to ethernet car or a real bridge. After
ifconfig eth1 down and ifconfig eth0 -promisc the same happened.

Below is the newwork configuration:

eth0 Link encap:10Mbps Ethernet HWaddr 00:00:C0:6A:30:8E
inet addr:157.181.6.125 Bcast:157.181.6.255 Mask:255.255.255.0
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:9921889 errors:0 dropped:0 overruns:0
TX packets:2462148 errors:2 dropped:0 overruns:0
Interrupt:10 Base address:0x290 Memory:dc000-e0000

eth1 Link encap:10Mbps Ethernet HWaddr 00:00:C0:6A:30:8E
inet addr:157.181.6.125 Bcast:157.181.6.255 Mask:255.255.255.0
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:118248 errors:0 dropped:0 overruns:0
TX packets:123297 errors:0 dropped:0 overruns:0
Interrupt:5 Base address:0x2d0 Memory:d4000-d8000

ppp1 Link encap:Point-Point Protocol
inet addr:157.181.6.125 P-t-P:157.181.101.1 Mask:255.255.255.0
UP POINTOPOINT RUNNING MTU:576 Metric:1
RX packets:456 errors:2 dropped:0 overruns:0
TX packets:305 errors:0 dropped:0 overruns:0

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
157.181.6.211 0.0.0.0 255.255.255.255 UH 0 0 8 eth1
157.181.101.1 0.0.0.0 255.255.255.255 UH 0 0 1 ppp1
157.181.6.0 0.0.0.0 255.255.255.0 U 0 0 672 eth0
157.181.101.0 0.0.0.0 255.255.255.0 U 0 0 11 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 31 lo
0.0.0.0 157.181.6.254 0.0.0.0 UG 1 0 800 eth0

Zoltan