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Possible fix for duplicated ARP entries in the FreeBSD stack


Hello,

For some time I've had problem with duplicated ARP entries that have caused all sorts of problems. I searched the archive and discovered that the problem had been reported before:


http://sourceware.org/ml/ecos-discuss/2004-11/msg00097.html



My proposal to a fix is to make the sockaddr_inarp struct (include/netinet/if_ether.h) equal in size to the sockaddr struct by padding it at the end. This is exactly what is done to the sockaddr_in struct (include/netinet/in.h) for different reasons.



I reached this conclusion after I discovered that two virutally identical calls to rtalloc1 (net/route.c) returned different results. The first instance appears in arplookup (netinet/if_ether.c) where the first parameter to rtalloc1 is a struct sockaddr_inarp cast to a struct sockaddr. The second instance appears in ip_output (netinet/ip_output) via rtalloc_ign (net/route.c) where the first parameter to rtalloc1 is an actual struct sockaddr. The rtalloc1 function does a radix tree search with a call to the rn_match function (net/radix.c). A closer look at this code reveals that it does indeed depend on the size of the supplied struct.



The only conclusion a can draw from this is that the three structs: sockaddr, sockaddr_in and sockaddr_inarp must all be of equal size. I have checked the FreeBSD source repository that this is the case for the original code.



While browsing the FreeBSD source repository I discovered that the sa_data character array member of the sockaddr struct was increased in size in the eCos FreeBSD stack. Does anyone know why this increase was introduced in eCos?


Regards,
SM

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