echo and echo reply

[aksher]

what is the difference between echo and echo reply in icmp permit any echo inside

and vice versa..

[Collin Clark]

One is a request, the other is the reply.

[aksher]

so does the request send only a request and reply both request and reply?

[sundar.palaniappan]

Hi,

ICMP echo-request is generated by the device from which the PING is originated. ICMP echo-reply is sent by the target device to the requesting device stating that it received the echo-request.

HTH

Sundar

[aksher]

my ques here is if yoou have only one either echo request or echo reply what will be the effect as given in command

icmp permit any echo-request inside

or

icmp permit any echo-reply inside

[a.kiprawih]

a. icmp permit any echo-request inside

- can send ping request to inside interface, but sender will not get reply.

b. icmp permit any echo-reply inside

- can get reply when pinging inside interface

To control ping request directed to your firewall interfaces, allow only specific ICMP type, i.e, allow only trusted IP/host to ping.

Carefully when allow ping to your outside interface from any internet/external host, esp to avoid ping/icmp attack.

http://www.cisco.com/en/US/customer/products/ps6120/products_command_reference_chapter09186a008063f9fd.html#wp1629224

http://www.rhyshaden.com/icmp.htm

http://groups.google.com.my/group/comp.security.firewalls/browse_thread/thread/2e4d1cf5ce99e9cf/27da7044c784e60e?lnk=st&q=why+ICMP+to+allow+request+reply&rnum=3&hl=en#27da7044c784e60e

Cheers!

AK