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Re: Router dumping core

At 10:40 AM 6/28/94, Matti Aarnio wrote:
>        Well, my latest code has something similar, but the limit is
>        on 4.. (that is, it tolerates 3 recursions)
>        I had some problems with CZ-landian networks where there
>        were two CNAMEs pointer to each other, and routers crashing
>        after spinning a few minutes on recursion..  (There should
>        be only one CNAME in any resolution.)

Ah...I hadn't grabbed the latest snapshot...I'll do so now...I was liberal
with my recursion-allowance 'cos I wasn't sure what the rules for CNAME
records were (I know that MX records cannot be nested, but I wasn't sure if
CNAMEs could be).

>> The core dumps from this turned out to not be directly useful for
>> debugging, since they were dumped after the stack was mangled, and thus,
>> all of the calling chain was lost.
>        No, you must be lucky to spot it BEFORE it happens, keep
>        router on debugger, and break it every now and then..

Exactly -- which is what I wound up doing.

Question -- do you, Matti, (or anyone else, or would Rayan like to speak
up) know why Rayan chose to do the recursion himself, rather than letting
the resolver library do it? One of the reasons it took me this long to plug
this hole (we've been bitten by this several times over the last couple
years) is because most of the other tools I use to dig for nameserver
problems failed gracefully with an error, rather than crashing...took me
until this time 'round to realize that Zmailer was doing it itself...

>> I should probably contribute back my fix for #2, shouldn't I...:-)
>        Well, if you found some new problem :)

Nope -- it sounds like you've fixed the same problem I did (the nameserver
recursion) at almost the exact same moment. The only reason I hadn't
already posted a patch is 'cos I was waiting for it to burn in and make
sure it did what it ought (I haven't even propagated it to my other
zmailer-running machines, yet...)


Michael Scott Shappe
CIT Collaboration Systems
"Me? I'm just a lawnmower. You can tell me by the way I walk."
        -- Genesis, "I Know What I Like", _Selling England by the Pound_
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