Should routers send redirects by default?

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Wed Aug 25 17:05:53 CDT 2010


On Wed, 25 Aug 2010 01:18:15 -0400
Christopher Morrow <christopher.morrow at gmail.com> wrote:

> On Tue, Aug 24, 2010 at 4:32 PM, William Herrin <bill at herrin.us> wrote:
> > On Fri, Aug 20, 2010 at 1:20 PM, Christopher Morrow
> > <christopher.morrow at gmail.com> wrote:
> >> Polling a little bit here, there's an active discussion going on
> >> 6man at ietf about whether or not v6 routers should:
> >>  o be required to implement ip redirect functions (icmpv6 redirect)
> >>  o be sending these by default
> >
> > Hi Chris,
> >
> > If you don't mind, I'd like to ask a similar question whose answers
> > might be instructive for the question you asked:
> 
> sure :) (other folks should also chime in, or I thought that was the
> spirit of your question...)
> 
> >
> > Forgetting all of the theoretical constructs for a moment, has anyone
> > here personally encountered an operational scenario in which ICMP
> > redirects solved a problem for you that you would otherwise have found
> > difficult or intransigent? Without naming names, would you describe
> > the scenario's details, explain the problem that would have existed
> > absent redirects and explain how redirects solved it for you?
> 
> I've never had redirects solve a problem for me.
> 

So how do you know?

If redirects are enabled by default, then they may have fixed a problem
for you that you didn't know existed and never realised existed. When
your packets get there successfully you don't go and investigate why.
You only troubleshoot failure, not success.

I think the only way to know an absolute answer would be to
have witnessed this sequence of events 

- have an environment where redirects are switched off

- suffer from a problem that redirects are designed to solve

- switch redirects on and have the problem not disappear

Of course, the problem not disappearing when redirects are enabled might
also mean a misdiagnosis of what the problem really is.

Regards,
Mark.




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