DROP or REJECT

DROP or REJECT

[HareRam]

Hi all

REJECT action tells tables to send back an ICMP message indicating that
you're REJECTing the packet.
DROPing will just DROP with no further action.

What is the Bandwidth will  use, if i keep on sending ICMP on big network
saying that
packets are REJECT.

which one i have to USE, recomendation will be more helpful

hare

DROP or REJECT

[Peter Marshall]

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Which is better (to drop or reject packets)?  I am asking more specifically for connections from the internet to my external firewall.

My second question is if I have a DNS in my DMZ (contains only ip's in my dmz.  internal boxes use this as their DNS.  This DNS falls back to my ISP), do I have to allow both TCP and UDP connections on port 53 ?  Can I not just have UDP, or does it use both ? 

Thank you.




Peter Marshall, BCS
Projects Division, CARIS 
115 Waggoners Lane, Fredericton NB, E3B 2L4 CANADA
Phone:  (506) 458-8533 (Reception) 
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Re: DROP or REJECT

[Frank Gruellich]

* Peter Marshall <peter.marshall@caris.com> 11. May 04:
> Which is better (to drop or reject packets)?  I am asking more
> specifically for connections from the internet to my external
> firewall.

REJECT is something more polite and suits to common standards.  However,
if your box is flooded with SYNs and your connection is disturbed you
maybe should start DROPing packets.

> My second question is if I have a DNS in my DMZ (contains only ip's in
> my dmz.  internal boxes use this as their DNS.  This DNS falls back to
> my ISP), do I have to allow both TCP and UDP connections on port 53 ?
> Can I not just have UDP, or does it use both ? 

Both.  HTH,
 regards, Frank.
-- 
Sigmentation fault

Re: DROP or REJECT

[Chris Brenton]

On Tue, 2004-05-11 at 09:45, Peter Marshall wrote:
> Which is better (to drop or reject packets)?  I am asking more
> specifically for connections from the internet to my external
> firewall.

Depends. I like rejecting with host-unreachables as it makes it look
like you do not have a firewall. It also has the ability to shut down
certain scanning tools before they can find exposed ports.

Some worry this could be a potential DoS situation. If you are worried
about this you can combine it with rate limiting.

> My second question is if I have a DNS in my DMZ (contains only ip's in
> my dmz.  internal boxes use this as their DNS.  This DNS falls back to
> my ISP), do I have to allow both TCP and UDP connections on port 53 ? 
> Can I not just have UDP, or does it use both ? 

Again, it depends. Queries use UDP/53 _unless_ the answer exceeds a 512
byte packet size. If it does, the connection can switch over to TCP/53. 

So, outbound you need TCP and UDP. Inbound to your DNS server, it
depends if you answers will exceed this maximum. If not, you only need
to permit UDP/53 from the Internet in general, and TCP/53 only from
servers (if any) that are acting as secondaries.

HTH,
Chris

Re: DROP or REJECT

[Frank Gruellich]

* Chris Brenton <cbrenton@chrisbrenton.org> 11. May 04:
> I like rejecting with host-unreachables as it makes it look like you
> do not have a firewall.

I hope you do this only in the FORWARD chain, don't you?

Just curious,
 regards, Frank.
-- 
Sigmentation fault

Re: DROP or REJECT

[Marc Haber]

On Tue, May 11, 2004 at 01:16:03PM -0400, Chris Brenton wrote:
> Depends. I like rejecting with host-unreachables as it makes it look
> like you do not have a firewall.

NACK. If I weren't there, the host unreachable would have the source
address of the upstream router, and not my own one. To be truly
invisible, you'd need to fake the upstream router's IP address, which
is (a) not easy to get hold of, (b) most probably not appreciated
by your upstream, and (c) some hosts will completely cease
communication with you which is not always the intended behavior.

Greetings
Marc

-- 
-----------------------------------------------------------------------------
Marc Haber         | "I don't trust Computers. They | Mailadresse im Header
Karlsruhe, Germany |  lose things."    Winona Ryder | Fon: *49 721 966 32 15
Nordisch by Nature |  How to make an American Quilt | Fax: *49 721 966 31 29

Re: DROP or REJECT

[Chris Brenton]

On Tue, 2004-05-11 at 14:17, Frank Gruellich wrote:
>
> * Chris Brenton <cbrenton@chrisbrenton.org> 11. May 04:
> > I like rejecting with host-unreachables as it makes it look like you
> > do not have a firewall.
> 
> I hope you do this only in the FORWARD chain, don't you?

Yup. Host unreachables originating from the host that is suppose to be
unreachable don't have quite the same effect. ;-)

C

Re: DROP or REJECT

[Chris Brenton]

On Tue, 2004-05-11 at 14:38, Marc Haber wrote:
>
> On Tue, May 11, 2004 at 01:16:03PM -0400, Chris Brenton wrote:
> > Depends. I like rejecting with host-unreachables as it makes it look
> > like you do not have a firewall.
> 
> NACK. If I weren't there, the host unreachable would have the source
> address of the upstream router, and not my own one.

I didn't say "not there", I said "look like there is no firewall". The
type 3 code 1 mimics the response of a typical router.

>  To be truly
> invisible, you'd need to fake the upstream router's IP address,

Not going to work. Firewalk will quickly identify there is a hop on the
wire that is not accounted for. Thus I don't bother shooting for
invisible, just a little bit of decoying and deception. ;-)

HTH,
Chris