From: Scott Morris (swm@emanon.com)
Date: Tue Aug 22 2006 - 15:35:36 ART
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
-----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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