04-29-2008 09:07 AM - edited 03-03-2019 09:44 PM
Can someone explain what ICMP exactly is and what is the proper command to enable ICMP.
-J
04-29-2008 09:13 AM
http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol
ICMP is a protocol so you can't enable and disable it, but you can control it.
04-29-2008 09:20 AM
makes sense,
my problem is this...
i am doing a tracert from the outside into my network, everything looks good until it gets to my router, after it hits the router it drops off. If I do the tracert internally, it "loops" though fine.
Any thoughts?
-J
04-29-2008 09:56 AM
Take a look at an ACL's (Access Control List) on your router/router's. You may see an entry that blocks ICMP from the outside as most companies do. For example, if you do an nslookup for google.com you get 64.233.187.99. Google allows you to ping this address. If you do an nslookup for microsoft.com you get 207.46.197.32. Microsoft doesn't allow you to ping this address.
04-29-2008 09:58 AM
So how do I unblock ICMP for what I need?
-J
04-29-2008 11:40 AM
It is not recommended to remove the ACL blocking external ICMP traffic into your network. If you want to modify the ACL, I suggest reading the following: http://www.cisco.com/en/US/products/sw/secursw/ps1018/products_tech_note09186a00800a5b9a.shtml.
Numbered ACL's do not allow you to remove just a single line. You would want to copy the entire ACL into notepad and then make your changes in notepad. Delete the ACL from the router and paste the new modified ACL from notepad. If you just tried to paste the modified ACL from notepad thinking it would overwrite the current ACL, the new lines would be added to the end of the current ACL.
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