Re: tlug: Netmask question

[Selva Nair <selva@example.com>]

On Mon, 21 Feb 2000, Julien Beasley wrote:

>  Hello everyone,
>  
>  I have a problem that I'm sure is simple to solve, but I've been stumped
>  on this. 
>  
>  When I connect via ppp to my ISP via gol, I am assigned an ip that is one
>  of the following forms:
>  
>  xxx.yyy.8.zzz
>  xxx.yyy.9.zzz
>  xxx.yyy.10.zzz

Guess you dont mean three identical digits by xxx, yyy etc. It may be
useful to know the last byte to see (from the subnet mask) which subnet
you belong to in each case. 

>  
>  
>  When I connect, I can always ping outside computers and do nslookup
>  regardless of which kind of ip I am assigned. However, I can only telnet,
>  irc, and www if I am assiged an ip of the form:
>  
>  xxx.yyy.8.zzz
>  
>  
>  So I can ping regardless of which ip I was assigned, but I can only use
>  other protocols if I have an ip that ends in xxx.yyy.8.zzz
>  
>  I happen to be using IP masquerading on this computer but I don't _think_
>  that has anything to do with it. The other computers behind the masq
>  behave the same way as the gateway computer. If the linux box has an 8.zzz
>  ip, the computer behind the masq can www and telnet. If not, it can only
>  ping.
>  
>  If I do an /sbin/ifconfig, it tells me that the netmask on my ppp
>  connection is 225.225.225.225. Is that wrong? 

If that is really the (sub)-netmask it is wrong. But do you mean
255.255.255.225? Even that is unusual as 225 will be a non-contigous bit
mask, something not very common (though the standard (RFC 950) does
permit it). I suppose that you are using dhcp, so that the netmask and
gateway addresses are obtained from the ISP's server. Do you have the 
same subnet mask for the all three IP addresses you mentioned? Also can
we see the output of ipconfig ?

>  
>  How can it be that I can ping in any case but I can only telnet and www if
>  I have an 8.zzz ip?
>  

I have no clear idea, but a possible guess is that you have some ppp
option (say header compression) which your server doesn't support.
ICMP packets of ping may get thru but not TCP packets of telnet.
But first let us get the netmask right.
 
Selva

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