02-20-2008 08:35 PM - edited 03-11-2019 05:05 AM
When setting up a CBAC (ip inspect) firewall on an IOS router should the "ip inspect" command be placed on the internal interface and use "ip inspect in" or should I use "ip inspect out" on the public or egress interface? What are the pros and cons of each?
Thanks,
Diego
02-20-2008 08:48 PM
IP Inspect should be applied on an interface so that packet could be processed before leaving that interface
example :- IP inspect always applied on direction "in" on interface interface (LAN) and always applied in out direction for public (wan interface
http://www.cisco.com/en/US/docs/ios/security/command/reference/sec_i2.html#wp1011411
02-21-2008 05:57 AM
Sorry, but that links just reiterates my comment that the inspect command can be used as "in" on the ingress and "out" on the egress. What I want to know is if there is any advantage or disadvantage of using one form or the other? I typically has used it as "in" on the ingress" but I have seem some examples using it as "out". Why?
Thanks,
Diego
02-21-2008 06:45 AM
okie let me explain in detail
Lets say you have 3 Interfaces on router e0,e1,e2
e1
|
Router--->e0-->(Internet)
|
|
e2
Now in case you want to inspect traffic originating from both 1 and 2 going to outside world then apply Inspect on e0 in "out" direction
In case you only need to monitor the traffic from e1 , then apply inspect on e1 in "in" direction
02-21-2008 02:58 PM
OK, I guess it saves you one line of config.
Thanks,
Diego
06-03-2008 03:20 AM
One difference I found from experience. When you want to inspect router generated traffic to the internet i.e. dns, icmp etc... you need to apply the inspect rule on the outside interface out.
If you apply it on the inside interface in it will not inspect router generated traffic such as DNS and ICMP even if you change the source interface to be inside.
p.s dont forget though for router generated traffic you also need to specify the router-traffic keyword on those inspects that support it such as....
ip inspect name Internet h.323 router-traffic
ip inspect name Internet sip router-traffic
ip inspect name Internet tcp router-traffic
ip inspect name Internet udp router-traffic
ip inspect name Internet icmp router-traffic
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