Outbound filtering question

Outbound filtering question

Post by ZeroUn » Wed, 05 Oct 2005 00:12:37



Hello,
in a LAN with Windows clients and Linux servers (on a domain controlled
by a Samba PDC) I would like to configure the following:

- any client has access to Internet, both web and email;
- only outbound transfers (any kind: HTTP, FTP, SMTP...) larger than
size X are blocked, and the failed attempt is logged; nothing else is
blocked or logged;
- some particular users have no limits, no transfers are blocked for
them.

What would you suggest?

Of course, I can live with it if I'm forced to change some requirements,
e.g. if I necessarily have to log everything.

Trying to accomplish all this, I started with squid. It can authenticate
against the Samba database, and it should be able to block outbound
transfers larger than X bytes thanks to the request_body_max_size
parameter (if I correctly recall its name), but it's a global setting,
it is applied to all users, and it's not what I need.
Then it also cannot be used for POP/SMTP.

Maybe I could use the "acl aclname req_header..." directive to
selectively check the HTTP request size?

And maybe I could use Postfix for SMTP filtering?
I could try with a SOCKS proxy like dante, but I think it does not have
the authentication and flitering features I need.

Any info is appreciated. Thanks.

01
--
Ciao,
  Marco.

 
 
 

Outbound filtering question

Post by ZeroUn » Wed, 05 Oct 2005 00:19:14


Hello,
in a LAN with Windows clients and Linux servers (on a domain controlled
by a Samba PDC) I would like to configure the following:

- any client has access to Internet, both web and email;
- only outbound transfers (any kind: HTTP, FTP, SMTP...) larger than
size X are blocked, and the failed attempt is logged; nothing else is
blocked or logged;
- some particular users have no limits, no transfers are blocked for
them.

What would you suggest?

Of course, I can live with it if I'm forced to change some requirements,
e.g. if I necessarily have to log everything.

Trying to accomplish all this, I started with squid. It can authenticate
against the Samba database, and it should be able to block outbound
transfers larger than X bytes thanks to the request_body_max_size
parameter (if I correctly recall its name), but it's a global setting,
it is applied to all users, and it's not what I need.
Then it also cannot be used for POP/SMTP.

Maybe I could use the "acl aclname req_header..." directive to
selectively check the HTTP request size?

And maybe I could use Postfix for SMTP filtering?
I could try with a SOCKS proxy like dante, but I think it does not have
the authentication and flitering features I need.

Any info is appreciated. Thanks.

01

 
 
 

Outbound filtering question

Post by ZeroUn » Wed, 05 Oct 2005 01:09:10




> Trying to accomplish all this, I started with squid. It can authenticate
> against the Samba database, and it should be able to block outbound
> transfers larger than X bytes thanks to the request_body_max_size
> parameter (if I correctly recall its name), but it's a global setting,
> it is applied to all users, and it's not what I need.

Uh-oh, maybe I was wrong here, and it CAN be used together with defined
acls so that it only applies (or it does not) to some users.
Anyway the other points in my request remain valid.

Thanks for any info.

01

 
 
 

1. IPTables filtering what should be allowed outbound traffic

Hello all,

I have a very simple firewall ruleset on a single interface which
should only be blocking everything inbound except to ports 22, 80, and
90.

My iptables rules are:


Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere           tcp
dpt:http
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:90
ACCEPT     tcp  --  anywhere             anywhere           tcp dpt:ssh

DROP       tcp  --  anywhere             anywhere

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

As you can see, I have no output filters defined.

The problem is, with these exact rules above loaded, I am unable to
send any outbound traffic save for ICMP.  For example, I can ping our
mail server, but I can not 'telnet mail.server.com 110', it just hangs.
 I would like to allow all outbound traffic from our server with no
restrictions.

I'm running Red Hat Linux release 8.0 (Psyche) with iptables v1.2.6a.

These same symptoms are present on an entirely different virtual server
we manage as well, so I must be missing something fundamental.  Anyone
know what it is?

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