Date: Sat, 20 Aug 2016 17:27:13 +0100 From: Bruce Simpson <bms@fastmail.net> To: Ryan Stone <rysto32@gmail.com> Cc: Ryan Stone <rstone@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r304436 - in head: . sys/netinet Message-ID: <091555f6-05a8-3f91-0486-beb6531abd34@fastmail.net> In-Reply-To: <6f4449f2-d145-8b49-c3f0-433e8ff4d2a2@fastmail.net> References: <201608182259.u7IMx5oW002018@repo.freebsd.org> <4fbc2e1d-3a62-5963-83d5-f9c931503e51@fastmail.net> <3806700d-ed27-7915-4818-c2d64f7b806d@fastmail.net> <CAFMmRNyi=PwE9pc9_8wCU63=HttUzFR4Zh2v=uHKcQ-zaLxdJQ@mail.gmail.com> <fcb33eac-ec99-03c7-57b5-f24f86c4f41a@fastmail.net> <CAFMmRNwDPy4Hd35DrfREZQzjvd89qw=zhEriddG8U8NV7tD=EA@mail.gmail.com> <6f4449f2-d145-8b49-c3f0-433e8ff4d2a2@fastmail.net>
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On 20/08/16 16:42, Bruce Simpson wrote: > On 20/08/16 16:27, Ryan Stone wrote: >> Can you send a broadcast packet through an L3 tunnel? I thought that a >> L2 tunnel was required. > > Yes. This is perfectly legal and necessary for forwarding of IPv4 > broadcasts to work. (it is Internet Protocol after all, not > Infernal-ethernet-extension Protocol. ;-)) For completeness: This does not hold true for L2 in L2, the most obvious example being Metro Ethernet VMAN style service. There, Ethernet is the transport (link layer), as well as the payload. That's a concrete example of the kind of L2 'tunnel' you may be referring to. Sometimes, specific Ethernet [broad|multi]cast destinations -- notably L2 control protocols, e.g. RSTP within the customer VLAN, may need to be tunnelled (Provider-Backbone-Bridges (PBB) style). Alternatively, the L2 destination MAC may be rewritten for that specific address, to avoid the destination being interpreted by routers in the Metro Ethernet core. It can be considered a crude form of Ethernet NAT, but it's common practice. But, for IP, forwarding IPv4 directed broadcast packets over a non-broadcast link is completely legal (and required for normal operation).
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