08-28-2015 12:47 PM - edited 03-11-2019 11:30 PM
Hi ASA allow to ping its interface by default. I notice that icmp permit any echo-reply inside can block ping from inside. Any one can explain the command for me ? Thank you
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08-29-2015 05:06 PM
Hi,
It's all to do with where you are pinging from.with regard to the ASA,as it is a Firewall then you want to control responses.
looking at it from the ASA point of view.
icmp permit any echo inside command allows devices on the inside network to ping the ASA and the ASA will reply. But it will not allow the ASA to ping the inside devices as we are not allowing echo-replies, so when you ping an inside device from the ASA the reply is dropped.
that's why you need the icmp permit any echo-reply inside, that will allow the reply from the ping from the ASA to the inside device to be received by the ASA.
Perhaps a look at the outside interface would be better.On the ASAs Public interface you don't want it to respond to Pings from the Internet, but you might want to ping the internet from the ASA, so in this case you would just have the icmp permit any echo-reply outside command,
so the ASA would allow replies to its own pings to devices on the Internet. but would not allow Internet devices to ping the ASA.
HTH
Richard.
08-28-2015 10:07 PM
Hi,
The icmp permit any echo-reply inside allows replies from the inside network to pings from the ASA
to allow pings from inside to the ASA you need icmp permit any echo inside.
To allow pings both ways you need both the commands.
08-29-2015 08:23 AM
Thank you so much for your reply. If we just use command icmp permit any echo inside, the inside network can ping the ASA, but if we just use command icmp permit any echo-reply inside, the inside network cannot ping the ASA. so the command icmp permit any echo inside already can control the icmp, why do we need the second command icmp permit any echo-reply inside ?
" The icmp permit any echo-reply inside allows replies from the inside network to pings from the ASA
to allow pings from inside to the ASA you need icmp permit any echo inside. "
I cannot understand it completely. Can you explain it again ? thank you
08-29-2015 05:06 PM
Hi,
It's all to do with where you are pinging from.with regard to the ASA,as it is a Firewall then you want to control responses.
looking at it from the ASA point of view.
icmp permit any echo inside command allows devices on the inside network to ping the ASA and the ASA will reply. But it will not allow the ASA to ping the inside devices as we are not allowing echo-replies, so when you ping an inside device from the ASA the reply is dropped.
that's why you need the icmp permit any echo-reply inside, that will allow the reply from the ping from the ASA to the inside device to be received by the ASA.
Perhaps a look at the outside interface would be better.On the ASAs Public interface you don't want it to respond to Pings from the Internet, but you might want to ping the internet from the ASA, so in this case you would just have the icmp permit any echo-reply outside command,
so the ASA would allow replies to its own pings to devices on the Internet. but would not allow Internet devices to ping the ASA.
HTH
Richard.
08-30-2015 01:38 PM
Excellent, Thank you!
You are welcome to below post
https://supportforums.cisco.com/discussion/12594161/anyone-can-help-understand-command-icmp-permit-any-unreachable-inside
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