[128963] in North American Network Operators' Group
Re: Should routers send redirects by default?
daemon@ATHENA.MIT.EDU (Jared Mauch)
Sat Aug 21 10:32:17 2010
From: Jared Mauch <jared@puck.nether.net>
In-Reply-To: <4C6FDEDF.2060400@brightok.net>
Date: Sat, 21 Aug 2010 10:32:00 -0400
To: Jack Bates <jbates@brightok.net>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
>=20
> 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).
>=20
> 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).
>=20
> 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!
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=
