in6_selectsrc() uses two different rtalloc calls depending on whether or
not the destination address is multicast or not, but there is nothing to
explain why. I dug a bit and found this commit from itojun@ :
diff -u -r1.6 -r1.7
--- src/sys/netinet6/in6_src.c 2000/06/18 04:49:32 1.6
+++ src/sys/netinet6/in6_src.c 2000/06/18 17:02:59 1.7
@@ -244,7 +244,11 @@
ro->ro_dst.sin6_family = AF_INET6;
ro->ro_dst.sin6_len = sizeof(struct sockaddr_in6);
ro->ro_dst.sin6_addr = *dst;
- if (!IN6_IS_ADDR_MULTICAST(dst)) {
+ ro->ro_dst.sin6_scope_id = dstsock->sin6_scope_id;
+ if (IN6_IS_ADDR_MULTICAST(dst)) {
+ ro->ro_rt = rtalloc1(&((struct route *)ro)
+ ->ro_dst, 0);
+ } else {
rtalloc((struct route *)ro);
}
}
Below are rtalloc() and rtalloc1() from sys/net/route.c r1.19 commited
on 05/21/2000 :
> void
> rtalloc(ro)
> register struct route *ro;
> {
> if (ro->ro_rt && ro->ro_rt->rt_ifp && (ro->ro_rt->rt_flags & RTF_UP))
> return; /* XXX */
> ro->ro_rt = rtalloc1(&ro->ro_dst, 1);
> }
>
> struct rtentry *
> rtalloc1(dst, report)
> register struct sockaddr *dst;
> int report;
> {
[...]
> /*
> * IP encapsulation does lots of lookups where we don't need nor want
> * the RTM_MISSes that would be generated. It causes RTM_MISS storms
> * sent upward breaking user-level routing queries.
> */
> miss: if (report && dst->sa_family != PF_KEY) {
> bzero((caddr_t)&info, sizeof(info));
> info.rti_info[RTAX_DST] = dst;
> rt_missmsg(msgtype, &info, 0, err);
> }
> }
> splx(s);
> return (newrt);
> }
So this if(MULTICAST) has been introduced to prevent RTM_MISS storms when
looking up routes to multicast addresses ; multicast and unicast route lookups
are the same.
Also, rtalloc(foo, RT_RESOLVE, bar) and rtalloc_mpath(foo, NULL, bar) are both
equivalent to _rtalloc(foo, NULL, RT_RESOLVE, bar).
Let's remove this if(MULTICAST), it's just confusing.
ok ?
Index: sys/netinet6/in6_src.c
===================================================================
RCS file: /cvs/src/sys/netinet6/in6_src.c,v
retrieving revision 1.71
diff -u -p -r1.71 in6_src.c
--- sys/netinet6/in6_src.c 2 Dec 2015 13:29:26 -0000 1.71
+++ sys/netinet6/in6_src.c 5 Dec 2015 12:03:48 -0000
@@ -240,13 +240,8 @@ in6_selectsrc(struct in6_addr **in6src,
sa6->sin6_len = sizeof(struct sockaddr_in6);
sa6->sin6_addr = *dst;
sa6->sin6_scope_id = dstsock->sin6_scope_id;
- if (IN6_IS_ADDR_MULTICAST(dst)) {
- ro->ro_rt = rtalloc(sin6tosa(&ro->ro_dst),
- RT_RESOLVE, ro->ro_tableid);
- } else {
- ro->ro_rt = rtalloc_mpath(sin6tosa(&ro->ro_dst),
- NULL, ro->ro_tableid);
- }
+ ro->ro_rt = rtalloc(sin6tosa(&ro->ro_dst),
+ RT_RESOLVE, ro->ro_tableid);
}
/*
