Date: Fri, 22 Jul 2011 10:28:50 +0400 From: Eygene Ryabinkin <rea@freebsd.org> To: Daniel Braniss <danny@cs.huji.ac.il> Cc: freebsd-net@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: broadcast oddity Message-ID: <jqVj%2B6q2ZvXWBaNJI89PeFrlHGM@%2BH3ezQp0vJIrviWzhz8TlqRT2d0> In-Reply-To: <E1QjTAs-000IjW-Ba@kabab.cs.huji.ac.il> References: <E1QioQt-000MJQ-T9@kabab.cs.huji.ac.il> <20110718203215.GM54929@MacBook-Eygene-Ryabinkin.local> <E1Qj4uZ-0005nH-SR@kabab.cs.huji.ac.il> <20110719172455.GP54929@MacBook-Eygene-Ryabinkin.local> <E1QjTAs-000IjW-Ba@kabab.cs.huji.ac.il>
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Wed, Jul 20, 2011 at 12:34:38PM +0300, Daniel Braniss wrote:
> from the diskless:
> els-01# ifconfig
> vr0: flags=3D8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 15=
00
> options=3D8280b<RXCSUM,TXCSUM,VLAN_MTU,WOL_UCAST,WOL_MAGIC,LINKST=
ATE>
> ether 00:0d:b9:22:57:18
> inet 132.65.91.1 netmask 0xfffff000 broadcast 132.65.95.255
> media: Ethernet autoselect (100baseTX <full-duplex>)
> status: active
> lo0: flags=3D8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
> options=3D3<RXCSUM,TXCSUM>
> inet 127.0.0.1 netmask 0xff000000=20
> els-01# netstat -rn
> Routing tables
>=20
> Internet:
> Destination Gateway Flags Refs Use Netif Expire
> default 132.65.80.1 UG 0 16606 vr0
> 127.0.0.1 link#4 UH 0 36 lo0
> 132.65.80.0/20 link#1 U 0 86612 vr0
> 132.65.91.1 link#1 UHS 0 12 lo0
>=20
> from the non-diskless:
> wrap-1# ifconfig
> sis0: flags=3D8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric=
0 mtu=20
> 1500
> options=3D83808<VLAN_MTU,WOL_UCAST,WOL_MCAST,WOL_MAGIC,LINKSTATE>
> ether 00:0d:b9:00:72:a8
> inet 132.65.80.181 netmask 0xfffff000 broadcast 132.65.95.255
> media: Ethernet autoselect (100baseTX <full-duplex>)
> status: active
> sis1: flags=3D8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500
> options=3D83808<VLAN_MTU,WOL_UCAST,WOL_MCAST,WOL_MAGIC,LINKSTATE>
> ether 00:0d:b9:00:72:a9
> media: Ethernet autoselect (none)
> status: no carrier
> lo0: flags=3D8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
> options=3D3<RXCSUM,TXCSUM>
> inet 127.0.0.1 netmask 0xff000000=20
>=20
> wrap-1# netstat -rn
> Routing tables
>=20
> Internet:
> Destination Gateway Flags Refs Use Netif Expire
> default 132.65.80.1 UGS 0 16936 sis0
> 127.0.0.1 link#4 UH 0 76 lo0
> 132.65.80.0/20 link#1 U 0 67433 sis0
> 132.65.80.181 link#1 UHS 0 0 lo0
The only difference I see is the absence of the 'S' flag on the default
route for the diskless case. Will try to create the testbed.
> > Yes, it is. But ip_output.c has the following code,
> > {{{
> > if (rte->rt_flags & RTF_GATEWAY)
> > dst =3D3D (struct sockaddr_in *)rte->rt_gateway;
> > if (rte->rt_flags & RTF_HOST)
> > isbroadcast =3D3D (rte->rt_flags & RTF_BROADCAS=
T);
> > else
> > isbroadcast =3D3D in_broadcast(dst->sin_addr, i=
fp);
> > }}}
> >=20
> > So, if the route that is selected is the gateway, then there will be
> > no broadcast on the L2. At least in my understanding of the code.
> > Thus, I am interested in the routing tables and route flags.
>=20
> so it boils down to a problem in selecting the route?
More-or-less so: for default gateways there will never be any
L2-broadcasts, for host routes the L2-broadcasts are governed by the
'B' route flag and for other routes the destination address governs
the behaviour (INADDR_ANY & INADDR_BROADCAST as the destination will
enable L2-broadcast unconditionally /but most likely we will hit the
default route earlier for this case/, interface broadcast address
/132.65.95.255 in your case/ will enable L2-brodcast via the
corresponding interface).
--=20
Eygene Ryabinkin ,,,^..^,,,
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