From owner-freebsd-net Sat Sep 1 19:46:30 2001
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Date: Sun, 2 Sep 2001 05:46:17 +0300
From: "Vladimir A. Jakovenko" <vovik@lucky.net>
To: freebsd-net@freebsd.org
Cc: freebsd-hackers@freebsd.org
Subject: SO_REUSEPORT on unicast UDP sockets
Message-ID: <20010902054617.A47742@lucky.net>
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Hello!
According to UNPv1 SO_REUSEPORT on UDP sockets can be used to bind more than
one socket to the same port (even with same source ip address). But quick
look on /sys/netinet/udp_usrreq.c function udp_input() shows that this will
work as expected (data stream duplicate) only on multicast/broadcast local
addresses. Please pay attention to the following code fragment comments:
if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
struct inpcb *last;
/*
* Deliver a multicast or broadcast datagram to *all* sockets
* for which the local and remote addresses and ports match
* those of the incoming datagram. This allows more than
* one process to receive multi/broadcasts on the same port.
* (This really ought to be done for unicast datagrams as
* well, but that would cause problems with existing
* applications that open both address-specific sockets and
* a wildcard socket listening to the same port -- they would
* end up receiving duplicates of every unicast datagram.
* Those applications open the multiple sockets to overcome an
* inadequacy of the UDP socket interface, but for backwards
* compatibility we avoid the problem here rather than
* fixing the interface. Maybe 4.5BSD will remedy this?)
*/
Is there still any real need in such backward compatibility? Can such
functionality be added (fixed) with possibility to switch it off using sysctl
or kernel-build option?
I find such possibility realy useful at least for NetFlow data processing and
believe that it would be useful for many UDP-based protocols.
--
Regards,
Vladimir.
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