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ICMP

Can someone explain what ICMP exactly is and what is the proper command to enable ICMP.

-J

5 REPLIES

Re: ICMP

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.

New Member

Re: ICMP

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

New Member

Re: ICMP

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.

New Member

Re: ICMP

So how do I unblock ICMP for what I need?

-J

New Member

Re: ICMP

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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