Ports Block

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Aug 26th, 2009
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We are facing problem of Spamming from our networks. Is there any command in cisco which we can execute on our cisco device to control or block ports responsible for spamming or If some other solution with anyone(except third party device or software) ...

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Joe Clarke Wed, 08/26/2009 - 09:00
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If the spamming is coming from a specific set of hosts, you can add an access-list to block the incoming SMTP traffic. For example:

access-list 101 deny tcp x.x.x.x any eq 25

access-list 101 deny tcp y.y.y.y any eq 25

access-list 101 deny tcp z.z.z.z any eq 25

action-list 101 permit ip any any

Then you can apply that ACL to your inbound interface:

interface Serial0

ip access-group 101 in

This is a pretty trivial example, and hard to maintain if you have a lot of spamming hosts. there are better solutions for spam such as a filter running on your SMTP server (e.g. the Open Source Spamassassin). The advantage of such filters is that they are adaptive, and can learn new types of spam.


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