firewall help / NEWBIE

firewall help / NEWBIE

Post by Ron Bombar » Mon, 19 Jul 1999 04:00:00



Greetings!

I have a Redhad Linux 6.0 box with a ppp connection to my ISP.  I have
SQUID running on it and am able to connect to the internet using my
WinBlows95 machine.
Works fine.

The BIG problem...... you all know.  Once I'm connected to the internet,
anyone and everyone can access my machine (and network).

I've been reading all the HOW-TO's and whatnot, but am still confused
about firewalls.  I'm trying to use ipchains to make it so that I (and
anyone else on my local network) can access the internet via sqiud
without granting ANY external access to my network.

Is this NOT a simple thing?

My linux box only has one NIC (eth0) and only one ppp interface (ppp0).
My local networks ipscheme is 192.168.100.X, my linux box being
192.168.100.129.  

I'm would think that this must be a VERY common scenario.

Can anyone give me some pointers?  I'll tell all my friends (all 2 of
them) what a nice person you are and that your voodo is the best!!!

Thanks.

Ron
--
Ron Bombard,  Network Administrator

PO Box 2567, Glens Falls, Ny 12801
http://members.theglobe.com/virtual_ron

Sometimes loosing a wife can be hard... in my
case it was nearly impossible!!!
---------------------------------------------------
   _O_        _____         _<>_          ___  
 /     \     |     |      /      \      /  _  \
|==/=\==|    |[/_\]|     |==\==/==|    |  / \  |
|  O O  |    / O O \     |   ><   |    |  |"|  |
 \  V  /    /\  -  /\  ,-\   ()   /-.   \  X  /
 /`---'\     /`---'\   V( `-====-' )V   /`---'\
 O'_:_`O     O'M|M`O   (_____:|_____)   O'_|_`O
  -- --       -- --      ----  ----      -- --  
  STAN         KYLE        CARTMAN       KENNY

 
 
 

firewall help / NEWBIE

Post by Fred Reime » Mon, 19 Jul 1999 04:00:00



> Greetings!

> I have a Redhad Linux 6.0 box with a ppp connection to my ISP.  I have
> SQUID running on it and am able to connect to the internet using my
> WinBlows95 machine.
> Works fine.

> The BIG problem...... you all know.  Once I'm connected to the internet,
> anyone and everyone can access my machine (and network).

> I've been reading all the HOW-TO's and whatnot, but am still confused
> about firewalls.  I'm trying to use ipchains to make it so that I (and
> anyone else on my local network) can access the internet via sqiud
> without granting ANY external access to my network.

> Is this NOT a simple thing?

> My linux box only has one NIC (eth0) and only one ppp interface (ppp0).
> My local networks ipscheme is 192.168.100.X, my linux box being
> 192.168.100.129.

> I'm would think that this must be a VERY common scenario.

> Can anyone give me some pointers?  I'll tell all my friends (all 2 of
> them) what a nice person you are and that your voodo is the best!!!

> Thanks.

> Ron
> --
> Ron Bombard,  Network Administrator

> PO Box 2567, Glens Falls, Ny 12801
> http://members.theglobe.com/virtual_ron

> Sometimes loosing a wife can be hard... in my
> case it was nearly impossible!!!
> ---------------------------------------------------
>    _O_        _____         _<>_          ___
>  /     \     |     |      /      \      /  _  \
> |==/=\==|    |[/_\]|     |==\==/==|    |  / \  |
> |  O O  |    / O O \     |   ><   |    |  |"|  |
>  \  V  /    /\  -  /\  ,-\   ()   /-.   \  X  /
>  /`---'\     /`---'\   V( `-====-' )V   /`---'\
>  O'_:_`O     O'M|M`O   (_____:|_____)   O'_|_`O
>   -- --       -- --      ----  ----      -- --
>   STAN         KYLE        CARTMAN       KENNY

Well first, you could make sure that your Linux box is not forwarding
traffic.  You can do a 'echo "0" > /proc/sys/net/ipv4/ip_forward' as root
to turn off IP forwarding.  Then you need to protect anyone from getting
directly to your Linux box.  You could try the following to block any
packets on your ppp0 interface that denies any packets that are trying to
start a connection:

ipchains -A input -J REJECT -p tcp -i ppp+ -y

This will not block UDP or ICMP packets, but at least it's a start.

Check out /usr/doc/ipchains-1.3.8/HOWTO.txt.  It's very helpfull...

hth,

fwr

 
 
 

firewall help / NEWBIE

Post by 9wand » Mon, 19 Jul 1999 04:00:00




> > Greetings!

> > I have a Redhad Linux 6.0 box with a ppp connection to my ISP.  I have
> > SQUID running on it and am able to connect to the internet using my
> > WinBlows95 machine.
> > Works fine.

> > The BIG problem...... you all know.  Once I'm connected to the internet,
> > anyone and everyone can access my machine (and network).

> > I've been reading all the HOW-TO's and whatnot, but am still confused
> > about firewalls.  I'm trying to use ipchains to make it so that I (and
> > anyone else on my local network) can access the internet via sqiud
> > without granting ANY external access to my network.

> > Is this NOT a simple thing?

> > My linux box only has one NIC (eth0) and only one ppp interface (ppp0).
> > My local networks ipscheme is 192.168.100.X, my linux box being
> > 192.168.100.129.

> > I'm would think that this must be a VERY common scenario.

> > Can anyone give me some pointers?  I'll tell all my friends (all 2 of
> > them) what a nice person you are and that your voodo is the best!!!

> > Thanks.

> > Ron
> > --
> > Ron Bombard,  Network Administrator

> > PO Box 2567, Glens Falls, Ny 12801
> > http://members.theglobe.com/virtual_ron

> > Sometimes loosing a wife can be hard... in my
> > case it was nearly impossible!!!
> > ---------------------------------------------------
> >    _O_        _____         _<>_          ___
> >  /     \     |     |      /      \      /  _  \
> > |==/=\==|    |[/_\]|     |==\==/==|    |  / \  |
> > |  O O  |    / O O \     |   ><   |    |  |"|  |
> >  \  V  /    /\  -  /\  ,-\   ()   /-.   \  X  /
> >  /`---'\     /`---'\   V( `-====-' )V   /`---'\
> >  O'_:_`O     O'M|M`O   (_____:|_____)   O'_|_`O
> >   -- --       -- --      ----  ----      -- --
> >   STAN         KYLE        CARTMAN       KENNY

> Well first, you could make sure that your Linux box is not forwarding
> traffic.  You can do a 'echo "0" > /proc/sys/net/ipv4/ip_forward' as root
> to turn off IP forwarding.  Then you need to protect anyone from getting
> directly to your Linux box.  You could try the following to block any
> packets on your ppp0 interface that denies any packets that are trying to
> start a connection:

> ipchains -A input -J REJECT -p tcp -i ppp+ -y

> This will not block UDP or ICMP packets, but at least it's a start.

> Check out /usr/doc/ipchains-1.3.8/HOWTO.txt.  It's very helpfull...

> hth,

> fwr

You might also give some serious thought to disabling rlogin, rtelnet,
etc. in your /etc/services file.

Regards, and Good Luck,
--
Beware the fury of a patient man.
     - John Dryden

 
 
 

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