[Click] kerneltun bypassing system routing table?

[Shaddi Hasan]

Hi all,


I have a simple IP-level forwarder, consisting of the following
configuration on two directly-connected machines. What I'd like to
have happen is all packets destined for 192.168.100.0/24 are routed
through Click, ipip encapsulated and forwarded to the second machine
(192.168.15.1) which is running a second instance of Click, listening
on the tun device at 192.168.35.1 (see routing table below).

Using tcpdump on the tun device, I see my traffic is being properly
encapsulated by Click with the proper destination address,
192.168.35.1, but no packets are routed through the eth1 device to the
other machine. I have verified no packets are getting transferred with
a physical tap (not KernelTap) on the line. What's confusing me is
that if I ping 192.168.35.1, I *do* get a response.

Is there something I am missing about the KernelTun element that would
cause packets sent to it in Click to bypass the system's routing
table? I'm not sure if this issue is due to a misconfiguration of
routing rules, misunderstanding of Click, misunderstanding of the tun
device, or a combination of the three, so apologies if this is not
actually a Click-related issue.

Thanks!
Shaddi


Click conf:
-------------------------------
AddressInfo(tun0 192.168.25.0/24);
tun :: KernelTun(tun0, DEVNAME tun0);

//Click interface from outside Tunnel to Tunnel
AddressInfo(tunIn 192.168.20.0/24);
kTunIn :: KernelTun(tunIn, DEVNAME tun_in);

kTunIn -> MarkIPHeader -> IPPrint(TUN_IN, LENGTH true) -> IPEncap(253,
192.168.25.1, 192.168.35.1) -> tun;

tun -> StripIPHeader -> MarkIPHeader -> IPPrint(TUN, LENGTH true) -> kTunIn;
-------------------------------

The relevant lines in my routing table look like this:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.35.1    0.0.0.0         255.255.255.255 UH    0      0        0 eth1
192.168.100.0   192.168.20.1    255.255.255.0   UG    0      0        0 tun_in
192.168.20.0    0.0.0.0         255.255.255.0   U     0      0        0 tun_in
192.168.35.0    192.168.15.1    255.255.255.0   UG    0      0        0 eth1
192.168.15.0    0.0.0.0         255.255.255.0   U     0      0        0 eth1
192.168.25.0    0.0.0.0         255.255.255.0   U     0      0        0 tun0