Summary:Telnet to Broadcast address

From: Janet Hoo (
Date: Tue Jun 24 1997 - 17:20:34 CDT

Thank you to J Bern, Bob Woodward and Mark H for your suggestions.
It turns out to be a problem with TCP/IP. Both Sun and Cisco confirmed
everything was configured correctly. Sun then attempted to duplicate the
problem and was able to, even with different versions of the OS.
Apparently, when you put only one machine on a subnet the it routes the
broadcast address to that machine instead of dropping it. Add a second
machine to the net and the problem disappears.

Here is the question incase, you missed it.

>Please HELP! I am really stuck. I have an Ultra 1 running 2.5.1 with

>all the latest patches. (The error occurred even before the patches were

>added) The machine is has a netmask of and it is the
>machine running on that subnet. The only thing between the machine and

>the router is a hub.
> Now, the problem. I am able to telnet into that machine through the

>broadcast address. We have three networks that have access to the
>machine and all can telnet into the broadcast address. The IP address
> and the broadcast address is When I
>into either address I get the same machine name and the same accounts
>work. For some reason either the Sun box is answering to .175 or the
>router is sending .175 to .173. I have had Cisco check the routing
>tables on the router and he says they are fine. I have also had a
>conference call with Sun and Cisco and both agree the broadcast address

>is correct for that subnet.
> I have tried changing the IP address, reloading the OS, Sys-unconfig

>the machine, and changing the hostname but nothing has worked.
> I have also checked the ifconfig -a, /etc/hosts, netstat table, arp
>table, /etc/services and they all appear normal. When I do a snoop of
>connection to .173 I see the machine name going back and forth to my IP

>address. When I snoop .175 I see the IP address going to my IP address

>not the name. I'm not sure if that is important? Another note, this
>machine is a standalone not running DNS or NIS. The network I am coming

>from is running NIS+ but we do not have that machine added to our DNS or

>NIS+ on any network. We can only get in by IP address.
> I have open tickets with both Sun and Cisco but neither has been able
>help. I am very concerned because this is suppose to be a secure
>machine. If you need any more information please e-mail me. I will
>summarize any answers. Thank you in advance!
> Janet L. Hoo
> Unix System Administrator

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