Hello,
The problem you described is also 2.1 kernel-versions.
When sending out packets, for syncPPP devices a 10 byte long fake header is
build (isdn_net.c:isdn_net_header), which later is removed
(isdn_ppp.c:isdn_ppp_xmit). tcpdump reads these outgoing packets with
fake-header from the packet-socket. Incoming packets don't have this header, so
here tcpdump works ok.
I have a patch for 2.1 kernels, which works fine for me, but i really dont
know, if it is the correct solution. Instead of creating a fake-header, it sets
dev->hard_header_len to ensure there is room in the header.
Lars Heete
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