Monthly Archives: April 2014

Understanding Prefix Lists

When filtering and manipulating routing protocols and routing updates there are a number of options on the Cisco platforms we as engineers can take advantage of.  In a previous post I briefly discussed the use of standard ACL’s to filter updates.  ACLs filter every packet, or in this case advertised network, that falls within the range is specifies.  This is useful for all or nothing or specific inclusions but does not allow us to us easily filter or permit based on the actual prefix length, ie subnet mask length.  Enter prefix lists. To begin the discussion lets establish a topology … Continue reading

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