On 07/05/2018 09:14 PM, Psyspy rambo wrote:
Hello, I am working on a kernel module in a Router that hooks into NF_INET_PRE_ROUTING to capture mDNS packets. Unfortunately, it doesn't see any packet. Interestingly, when tcpdump is running in promiscuous mode, the kernel module sees mDNS packets. One would think that these multicast packets will be visible at least to PRE_ROUTING hook, then the routing code may either drop it or send it to other hooks. Any reason netfilter doesn't see these multicast packets? I would appreciate any ideas to resolve this issue. Thanks.
Switches should only forward multicast packets to hosts that subscribe to the destination multicast address. Promiscuous mode causes the switch to forward all the packets regardless.
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