Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!dcatla!zdwcv
From: zdwcv@dcatla.UUCP (Wm. C. VerSteeg)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: subnet mask problem
Message-ID: <19331@dcatla.UUCP>
Date: 25 May 89 18:14:35 GMT
References: <6200023@hpindda.HP.COM>
Reply-To: bvs@NRC.COM (Wm. C. VerSteeg)
Organization: DCA, Inc., Alpharetta, GA
Lines: 30

In article <6200023@hpindda.HP.COM> tozz@hpindda.HP.COM (Bob Tausworthe) writes:
>
>1) is a mask such as 255.255.0.255 even legal (i.e. conform to specifications)
>
>2) does anybody know of a network user whose mask is of the form above.
>
>			     tozz@hpda.hp.com


RFC950 clearly states that subnet bits need not be contiguous. However, I 
have not seen any networks that have been configured to use non-contiguous
masks. 

I have been looking at a situation where a host sends a bogus ICMP mask 
reply. The device who is looking to resolve his network mask sees this
reply and trusts it. This device then can't talk to his own local network,
because he has accepted a bogus network mask. A human looking at address
masks can probably decide whether or not a particular mask is bogus or not.
For instance, a mask reply on a class C network of 101.214.1.77 is obviously
bogus. Is there an algorithm for determining whether to trust a mask response?


The obvious solution to this problem{is to shoot the person who wrote 
the code that returns the bogus mask  but this is not very  pratical (|-)).

What I would like to do is use some code that throws away the obviously 
bad responses. Is there an algorithm in use to do this ?


Bill VerSteeg