On Sat, 21 Aug 2010 10:32:00 -0400 Jared Mauch <ja...@puck.nether.net> wrote:
> > On Aug 21, 2010, at 10:12 AM, Jack Bates wrote: > > > Eric J. Katanich wrote: > >> You disable it on the host and if no host is using it, you might as well > >> disable it on the router as wel. Others mentioned > >> some routers need to handle this in software instead of hardware, which is > >> obviously slower. > > > > Most redirects are limited in their rate, so it generally is unnoticed on > > the router, but yes, to be fully optimized, turning it off isn't a bad > > idea. Here's a better one. Put the router's choice in the RA on a per > > prefix basis (and of course DHCPv6 for non-RA setups). > > > > Any router/host communication agreements really should have a profile > > setup. If the router is acting in a certain way, it should be able to > > notify the host. If RA is disabled and a pure DHCPv6 setup was deployed, > > obviously the DHCPv6 server would need to provide the necessary router > > information (mtu, icmp unreachable support, etc). > > > > It bugs me that we setup automation support such as between routers and > > hosts and don't include all the different details that both really should > > agree on (such as icmp redirects, or even the ability to push routes to > > hosts, ie modify redirects to support prefix or host based redirects since > > we are starting over here). > > One of the use cases for the redirects listed is that someone may DHCPv6 a > prefix, but (!!!) not know the netmask of the prefix, so may not know what is > on-net. ie: here's your host address, good luck! > That's not the case. What they're saying is that an address by itself does not _imply_ a prefix length i.e. don't assume a /64. This isn't any different to IPv4 in the last 15 years - "192.168.0.1" by itself doesn't imply a /24 since CIDR came along. RFC5942 does into details. Basically it says if a node doesn't have a separate indication that a prefix is onlink (i.e. via a configured prefix length, or via PIO options in an RA), then don't assume the internal structure of the address is known (i.e. don't assume a /64). > This surely isn't something I had expected as an output of the IETF, as i > figured that even the most basic folks advocating for "internet engineering" > would tell a host the netmask so it would know what is on-net vs off-net. > > This tells me that the use of redirects isn't quite as straightforward as > "helping" but more as "crutch" for not wanting to consume an extra byte for > mask and few bytes for a default-router. > > It also means they are unlikely to be as limited in their rate as you > suggest, it will make the IPv6 router look more like a flow-swithced device > (having to send a redirect for each subnet/mask that is different) and > effectively make the host participate (via redirects) in this routing > protocol. > > - Jared
