Should routers send redirects by default?

Warren Kumari warren at kumari.net
Wed Aug 25 10:01:23 CDT 2010


On Aug 24, 2010, at 4:32 PM, William Herrin 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:
>
>
> 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 have, but it was a long long time ago (~1997), and it was a stupid  
problem....

We had a bunch of hosts on a LAN - their default GW was an AGS+  
connected to provider X. Also on the same network was a Bay Networks  
BCN (AFAIR) connected to provider Y.

In general most flows were relatively long lived (some NNTP, some  
FTP.. oh, and Quake!). There was no reasonable way to inform the hosts  
if provider X went away. The AGS+ would also run a bit too hot if it  
had to accept all of the traffic and then punt the relevant parts over  
to the BCN....

Unrelated, but this network also did static IPs for dial customers  
(who could dial into one of ~lots of RAS boxes) -- this meant that the  
RAS boxen has to inject /32s into OSPF for each customer -- this meant  
that if certain routers (like the AGS+) bounced there was enough churn  
that other routers would fall over (the BCN would hit some watchdog  
and fall over, and if you tried to bring it up into a network that was  
already converged it would run out of RAM and happily drop into some  
debugger console).

Fun times...

W



>
> Thanks,
> Bill Herrin
>
>
>
>
>
>
> -- 
> William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
> 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
> Falls Church, VA 22042-3004
>

--
She'd even given herself a middle initial - X - which stood for  
"someone who has a cool and exciting middle name".

     -- (Terry Pratchett, Maskerade)






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