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05.10.2008 at 03:04AM PDT, ID: 23391445
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7.9

Simple Command to disable icmp on External Interface

Zones: Network Routers, Internet Control Message Protocol (ICMP), Cisco PIX Firewall
Tags: Cisco, 2811 Router, Advanced IP services, Used as a VPN Endpoint
Hello all and thanks for any suggestions you may have.

The Cisco ASA (5500) has a simple command to disable and enable ICMP on its interfaces

icmp deny any outside
icmp permit any inside

Is there a very simple way to disable pings (icmp) on an external Interface.

I've attached my config (actually) from an 871 but the IOS level is similar and virtually the same except for the interfaces.

Thanks all
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70WEST#sh run
Building configuration...
 
Current configuration : 2241 bytes
 
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
 
hostname 70WEST
 
boot-start-marker
boot-end-marker
 
enable secret 5 xxxxxxxxxxxxxxxxxxxxx
enable password 7 xxxxxxxxxxxxxxxxxxxxxxxxxx
 
no aaa new-model
ip cef
no ip dhcp use vrf connected
ip dhcp excluded-address 10.2.2.1 10.2.2.19
ip dhcp excluded-address 10.2.2.51 10.2.2.255
 
ip dhcp pool WESTPOOL
   network 10.2.2.0 255.255.255.0
   default-router 10.2.2.1
   domain-name xxxxxxxxxx.com
   dns-server 10.1.10.20 10.1.10.23
   netbios-name-server 10.1.10.23
 
 
no ip domain lookup
 
crypto isakmp policy 10
 encr 3des
 hash md5
 authentication pre-share
crypto isakmp key xxxxx address x.x.x.x no-xauth
 
crypto ipsec security-association lifetime seconds 86400
 
crypto ipsec transform-set aes256-1 esp-3des esp-md5-hmac
 
crypto map outside-map-1 1 ipsec-isakmp
 set peer x.x.x.x
 set transform-set aes256-1
 match address 101
 
interface FastEthernet0
 
interface FastEthernet1
 
interface FastEthernet2
 
interface FastEthernet3
 
interface FastEthernet4
 ip address x.x.x.x 255.255.255.252
 ip nat outside
 ip virtual-reassembly
 duplex auto
 speed auto
 crypto map outside-map-1
 
interface Vlan1
 ip address 10.2.2.1 255.255.255.0
 ip nat inside
 ip virtual-reassembly
 
ip default-gateway x.x.x.x
ip route 0.0.0.0 0.0.0.0 x.x.x.x name DEFAULT_ROUTE
 
no ip http server
no ip http secure-server
ip nat inside source list 100 interface FastEthernet4 overload
 
ip access-list extended outside_cryptomap_1
 permit ip 10.2.2.0 0.0.0.255 any
 
access-list 95 permit x.x.x.x
access-list 95 permit x.x.x.x
access-list 95 permit 10.1.8.0 0.0.3.255
access-list 100 deny   ip 10.2.2.0 0.0.0.255 10.1.8.0 0.0.3.255
access-list 100 permit ip 10.2.2.0 0.0.0.255 any
access-list 101 permit ip 10.2.2.0 0.0.0.255 10.1.8.0 0.0.3.255
access-list 150 permit ip 10.2.2.0 0.0.0.255 any
dialer-list 1 protocol ip permit
 
 
 
control-plane
 
 
line con 0
 no modem enable
line aux 0
line vty 0 4
 access-class 95 in
 password 7 xxxxxxxxxxxxx
 logging synchronous
 login
 transport input telnet ssh
 
scheduler max-task-time 5000
end
 
70WEST#
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Question Stats
Zone: Security
Question Asked By: Citadelny
Solution Provided By: decoleur
Participating Experts: 2
Solution Grade: B
Views: 42
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05.10.2008 at 06:18AM PDT, ID: 21538945
tztrh:

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05.10.2008 at 07:49PM PDT, ID: 21541316
decoleur:

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05.16.2008 at 09:48PM PDT, ID: 21588031
Citadelny:

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05.16.2008 at 09:54PM PDT, ID: 21588038
Citadelny:

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05.17.2008 at 03:43AM PDT, ID: 21588673
decoleur:

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06.09.2008 at 12:05PM PDT, ID: 21745696
Citadelny:

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06.09.2008 at 12:47PM PDT, ID: 21746039
Citadelny:

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06.09.2008 at 01:13PM PDT, ID: 21746244
decoleur:

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06.09.2008 at 01:56PM PDT, ID: 21746607
Citadelny:

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06.10.2008 at 07:31AM PDT, ID: 21751617
Citadelny:

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05.10.2008 at 06:18AM PDT, ID: 21538945
tztrh:
create access list and deny icmp
 
05.10.2008 at 07:49PM PDT, ID: 21541316
decoleur:
ip access-list extended outside_acl_in
 deny icmp any any
 permit ip any any
exit
interface fastethernet4
ip access-group outside_acl_in in
exit

hope this helps,

-t
 
05.16.2008 at 09:48PM PDT, ID: 21588031
Citadelny:
It would seem an ACL is the way to go but adding the lines suggested by decoleur actually stopped my outgoing traffic because my NAT was already using ACL 100.

I took both suggestions and tried changing ACL 100 to include denies for icmp but the outside int still responds.

My updated acl 100 looks like this
access-list 100 deny   ip 10.2.2.0 0.0.0.255 10.1.8.0 0.0.3.255
access-list 100 deny icmp any any
access-list 100 permit ip 10.2.2.0 0.0.0.255 any

Thanks
 
05.16.2008 at 09:54PM PDT, ID: 21588038
Citadelny:
Can You have two acls assigned to one interface?
 
05.17.2008 at 03:43AM PDT, ID: 21588673
decoleur:
you can have one ACL applied to an interface in both directions, so you can have two, one inbound and one outbound on each interface.
 
06.09.2008 at 12:05PM PDT, ID: 21745696
Citadelny:
I have one currently - that is acl 100 and that controls the flow out but I'm not sure how to addd the one for incoming traffic - I know how to do a static but the block icmp acl eluses me

Send code if possible - also if it affects how acl 100 OUT is applied please indicate how it should be adjusted.

Thanks all
 
06.09.2008 at 12:47PM PDT, ID: 21746039
Citadelny:
following decoleur's suggestion , I found out how to apply the access-group command to the interface and I added this to the acl

ip access-list extended outside_acl_in
 deny   tcp any any eq echo
 permit ip any any

But the best I could get it to do was to give me a destination unreachable when I ping the outside interface and I want the packets to be dropped - I want no response from the router.

Thanks
 
06.09.2008 at 01:13PM PDT, ID: 21746244
decoleur:
make sure the command is "deny icmp any any eq echo" you typed deny tcp any any eq echo in your descrption.

looking at http://www.experts-exchange.com/Hardware/Networking_Hardware/Routers/Q_21158242.html you could add "deny udp any any gt 32768" before the "permit ip any any" to block trace route as well.

This is only going to work from the outside in.

hope this helps,

-t
Accepted Solution
 
06.09.2008 at 01:56PM PDT, ID: 21746607
Citadelny:
I started messing with tcp as the option because the router started kicking back Destination unreachanble which is "better" but still a response. even with the config you just pointed to it still giving DUNRs
not req timed out like I wish it would.

Thanks for your attention
 
06.10.2008 at 07:31AM PDT, ID: 21751617
Citadelny:
DECOL's solution got me to the point where the router sent back unreachables. Which was sort of ok but it was a response nontheless. I added "no ip unreachables" to the interface and that killed the responses. I now have what I wanted
 
 
20080716-EE-VQP-33 / EE_QW_2_20070628