Date: Fri, 6 Mar 2020 08:16:01 +0100 From: =?utf-8?Q?Dennis_K=C3=B6gel?= <dk@neveragain.de> To: Philip Homburg <pch-fbsd-2@u-1.phicoh.com> Cc: freebsd-net@freebsd.org Subject: Re: Revisiting FreeBSD-SA-08:10.nd6 (or: avoiding IPv6 pain) Message-ID: <97992D2A-CE25-44DB-8441-1C2F3A43C1B2@neveragain.de> In-Reply-To: <m1j9pbX-0000F6C@stereo.hq.phicoh.net> References: <m1j9pbX-0000F6C@stereo.hq.phicoh.net>
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Am 05.03.2020 um 13:27 schrieb Philip Homburg <pch-fbsd-2@u-1.phicoh.com>: > In your letter dated Wed, 4 Mar 2020 21:10:09 +0100 you wrote: >> This flag was introduced in a 2008 Security Advisory, because "non-neighbors" >> could abuse Neighbor Discovery to potentially cause denial-of-service situatio >> ns. >> In my situation it caused valid Neighbor Solicitation packets from my provider >> to be silently dropped, making the connection effectively unusable. > > In theory, the onlink status of a prefix should be announced in in > router advertisements and should be consistent across all nodes on a > subnet. In that sense, if this check fails then the network is misconfigured. Good point, and probably an indication that my provider's setup is broken. But in terms of RFC-perspective, RAs and ND are not strictly related, I believe - for example, prefixes might have been configured manually (?). > That said, there is a specific check in processing Neighbor Discovery packets > that the hop limit is equal to 255. In that sense any node that manages to > send a packet with hop limit 255 is a neighbor, so I don't quite see how there > could be an attack by non-neighbors. Exactly, that's where I couldn't understand the Advisory. Though it seems to focus in router nodes, and not host nodes. - D.
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