Thanks to those of you who responded earlier. None of the suggestions
worked, but they all seemed reasonable and did sort of lead to where I am
now, which is better than before. 8-)
OK, here's a quick recap:
I have two Linux boxen to connect two groups of PCs across an intervening
LAN/WAN. IP tunnelling works fine between the two nets - EXCEPT for the
one thing I need, which is for UDP packets sent to 255.255.255.255 to
appear on both sides of the tunnel. Here's a somewhat simplified diagram
of the setup:
LAN1 10.42.2.131 10.75.78.221 LAN2
==============| eth0 eth0 |==============
10.42.250.0/24|----GW1---------//-----------GW2----|10.75.250.0/24
==============|eth1 eth1|==============
10.42.250.1 10.75.250.1
Hosts on LAN1 and LAN2 can communicate. I need broadcasts sent to
255.255.255.255 from LAN1 to show up on LAN2 and vice versa. Originally
packets sent to 255.255.255.255 went NOWHERE past the gateways, no matter
what I did. I had to hack net/ipv4/route.c in the kernel source to remove
the lines that prevent any broadcast packets from being forwarded (look at
line 1519 or so). Now the kernel will forward broadcasts.
I entered host routes for 255.255.255.255 on both sides, so the routing
tables look like so:
on GW1:
Destination Gateway Genmask Flags Metric Iface
255.255.255.255 10.75.78.221 255.255.255.255 UH 0 tunl0
10.42.2.0 0.0.0.0 255.255.255.0 U 0 eth0
10.42.250.0 0.0.0.0 255.255.255.0 U 0 eth1
10.75.250.0 10.75.78.221 255.255.255.0 UG 0 tunl0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 lo
0.0.0.0 10.42.2.31 0.0.0.0 UG 0 eth0
(GW2 looks the same but reversed, and of course the default route is
different).
If I ping 255.255.255.255 from anywhere, I get an answer from the opposite
gateway - i.e., if I ping from LAN1 I get an answer from the eth0 address
on GW2, ping from LAN2 gets an answer from GW1. If I add the host route
with no gw and dev tunl0, pings to 255.255.255.255 result in an error
message in syslog "kernel: tunl0: Packet with no target gateway!". Any
other way I've tried results in no ping reply at all, and none of the
things I've tried gets me where I need to be - seeing packets sent to
255.255.255.255 from LAN1 appear on LAN2 and vice versa.
Bright ideas, anyone? Is there something I missed?
Dale
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