From: David Redfern \(AU\) (David.Redfern@didata.com.au)
Date: Thu Aug 24 2006 - 06:39:39 ART
Guys,
As i think we can all agree that the answer may vary depending on the
question and requirements, i suggest we pose a few different
hyptothetical sample questions to each other, so that we can see how
certain KEYWORDS and requirementes affect the answer.
Here's one.
Internal network address range is 1.1.X.0/24
Router 1 has an E0/0 link to the backbone (BB1)
Question
Your network has become extremely slow and you suspect a DOS attack
coming from BB1.
Create an acl which will log icmp flood/smurf attacks to your logging
buffer.
Create this acl on R1 in a manner which will assist you to distinguish
between these attacks wherever possible.
________________________________
From: Scott Morris [mailto:swm@emanon.com]
Sent: Thursday, 24 August 2006 6:09 AM
To: 'Aamir Aziz'; 'David Mitchell'
Cc: 'Chris Broadway'; 'Peter Plak'; 'Victor Cappuccio'; 'Dusty'; David
Redfern (AU); ccielab@groupstudy.com
Subject: RE: ICMP Flooding vs SMURF Attack---THE BRIANS AND SCOTT
I'll stick with the answer of "it depends" :)
in your first one, you are assuming that all links are /24. Which may
be true, but you'll have to look at your topology to assess that!
in the second one, it certainly blocks it all, which again may or may
not be what you want to accomplish.
There is NO SINGLE answer!
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE #153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP - Curriculum Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
________________________________
From: Aamir Aziz [mailto:aamiraz77@gmail.com]
Sent: Wednesday, August 23, 2006 3:11 PM
To: David Mitchell
Cc: Scott Morris; Chris Broadway; Peter Plak; Victor Cappuccio; Dusty;
David Redfern (AU); ccielab@groupstudy.com
Subject: Re: ICMP Flooding vs SMURF Attack---THE BRIANS AND SCOTT
Hi all
Many thanks for the all the replies. Ok so if i build the following ACL
(lets say on edge router) to protect myself from being the REFLECTOR and
the VICTIM for SMURF/Fraggle attack would this work:
deny icmp any 0.0.0.255 <http://0.0.0.255/> 255.255.255.0
<http://255.255.255.0/> echo
deny icmp any 0.0.0.0 <http://0.0.0.0/> 255.255.255.0
<http://255.255.255.0/> echo
deny icmp any 0.0.0.255 <http://0.0.0.255/> 255.255.255.0
<http://255.255.255.0/> echo-reply
deny icmp any 0.0.0.0 <http://0.0.0.0/> 255.255.255.0
<http://255.255.255.0/> echo-reply
deny udp any any eq echo
deny udp any eq echo any
permit ip any any
or this one (from
http://www.cisco.com/en/US/tech/tk59/technologies_tech_note09186a0080149
ad6.shtml#topic3)
deny icmp any any echo
deny icmp any any echo-reply
deny udp any any eq echo
deny udp any eq echo any
permit ip any any
Which of them would work? If both then which is appropriate for CCIE
lab, if neither then what is missing here.
Many thanks
Aamir
On 8/23/06, David Mitchell <david.mitchell@centientnetworks.com> wrote:
If my understanding of Smurf attacks is correct, your strategy
would
succeed in stopping you from being the REFLECTOR, but not the
VICTIM.
If you are the VICTIM of a Smurf attack, the packets you will be
seeing
will be unicast icmp echo-reply packets sourced from the
REFLECTOR to
your address. This would be because the attacker spoofed your
address
range and sent the icmp echo-requests to the reflector's
broadcast
address, resulting in the reflector responding with the
echo-reply's to
your addresses.
If my understanding is correct, you would need to filter out
icmp
echo-reply packets on the edge to stop this.
Hopefully I understand this properly. So far I'm a two-time
Security
lab failure!!
- Dave
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf Of
Scott Morris
Sent: Wednesday, August 23, 2006 12:17 PM
To: 'Aamir Aziz'
Cc: 'Chris Broadway'; 'Peter Plak'; 'Victor Cappuccio'; 'Dusty';
'David
Redfern (AU)'; ccielab@groupstudy.com
Subject: RE: ICMP Flooding vs SMURF Attack---THE BRIANS AND
SCOTT
If you are looking to stop an attack TO a router, I'd use:
no ip directed-broadcast (on each interface)
no service udp-small-servers (which will shut down those udp
ports)
I believe both may be defaults now (Cisco is occasionally nice).
If you have to filter on an edge, which makes more sense, I
believe both
Brian and I have offered multiple methods of accomplishing this.
One is
not
necessarily better than another. Below, I lay out the port
numbers for
you,
so build an ACL matching each of those in udp as well as ICMP
echo
coming
in.
Building the ACL shouldn't be a difficult exercise as you know
the
information below. In the middle of your exam (IMHO) you won't
be
required
to memorize the multiple ports that a Fraggle attack may go
after unless
it
is mentioned someplace on the DocCD. So build away! Come up
with one
and
let's see what you got!
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
#4713,
JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP - Curriculum Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
_____
From: Aamir Aziz [mailto:aamiraz77@gmail.com]
Sent: Wednesday, August 23, 2006 10:09 AM
To: swm@emanon.com
Cc: Chris Broadway; Peter Plak; Victor Cappuccio; Dusty; David
Redfern
(AU);
ccielab@groupstudy.com
Subject: Re: ICMP Flooding vs SMURF Attack---THE BRIANS AND
SCOTT
Dear Mr.Brian & Mr.Scott,
Thank you for the valuable input, i think it was really helpfull
but
lets
say in the exam if they clearly mention that it is a
SMURF/Fraggle
attack
and we need to stop it using ACL then in your expert opinion
what ACL
should
we use on the router?
Thanks
Aamir
On 8/22/06, Scott Morris <swm@emanon.com> wrote:
Well, look at the two attacks and what they are first.
Smurf is an ICMP-based attack. Typically the echo-request
packets are
sent
TO the subnet-broadcast address. This is simply stopped (and by
default)
with "no ip directed-broadcast" on a LAN. Or you can filter on
an edge
router closer to the Internet link using an extended ACL.
Being that most Smurf attacks are also from spoofed addresses,
"ip
verify
unicast reverse-path" or "ip verify unicast source reachable via
any"
could
help. (<--RFC 2267) You could also rate-limit the information,
but this
isn't the best solution!
Fraggle is the same type of attack, except that it involves UDP
packets
instead of ICMP ones. Typically it's directed at common
unix-based echo
ports (7, 13, 17, 19). So the same methods will protect you.
For TCP SYN attacks, that usually involves a bunch of embryonic
(half-open)
connections going on. Short of your router(s) monitoring the
number of
initial TCP open requests that come in, there's not many good
ways to do
this! Firewalls (including CBAC) are certainly the best ways,
but not
on
the R&S exam!!!
You may have TCP Intercept on your exam covered by some of the
more
generic
security features listed on the Blueprint! Look in the same
security
command reference where the RPF information is at, and you'll
see "ip
tcp
intercept" for some information on that.
While you could rate-limit with an acl matching "tcp any any
syn". Like
many things which thing you choose as your solution may depend
on
requirements of the lab!
Just my thoughts...
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
#4713,
JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP - Curriculum Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com <http://www.ipexpert.com>
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf Of
Chris Broadway
Sent: Tuesday, August 22, 2006 11:21 AM
To: Peter Plak
Cc: Victor Cappuccio; Dusty; David Redfern (AU); Aamir Aziz;
ccielab@groupstudy.com
Subject: Re: ICMP Flooding vs SMURF Attack---THE BRIANS AND
SCOTT
Group,
Can we get the "Brians" and/or Scott to give us their opinion on
the
definitive ACL to log smurf, fraggle, and TCP syn attacks? I
think
everyone
has an opinion but have not heard from the ones I consider to be
the
most
trusted sources.
-Broadway
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