Re: Invalid IP address

From: David Pick (d.m.pickat_private)
Date: Tue Oct 22 2002 - 00:14:10 PDT

  • Next message: Dave Phelps: "Re: Invalid IP address"

    > You seem to be correct, someone on 68.84.8.41 is trying to access various
    > other sites. One thing that is confusing in the log entries is the port
    > number (0) which is being reported. Cisco access lists log the entry as
    > port 0 when you don't explicitly specify the port number in the access
    > list, so an ACL like :
    > 
    > access-list 100 deny ip 10.0.0.0 0.255.255.255 any log
    > 
    > will create logs with port 0 as the port, however ACLs like :
    > 
    > access-list 100 deny tcp 10.0.0.0 0.255.255.255 any range 0 65535 log
    > access-list 100 deny udp 10.0.0.0 0.255.255.255 any range 0 65535 log
    > access-list 100 deny ip 10.0.0.0 0.255.255.255 any log
    > 
    > will log the port numbers and produce a more understandable output - ie.
    
    To be more precise, several releases of IOS logged port 0 when
    the log entry was produced by an access-list entry that did
    not check the port number ***and no previous entry had checked
    the port number*** so the port number had never actually been
    extracted from the packet. An ACL entry that did not specify
    a port number but caused a log event got it right if a previous
    entry in the ACL had checked the port number.
    
    The example above is correct but, depending on the individual
    lists concerned, not necessarily necessary.
    
    I'm sorry, I can't recall which version numbers were relevant.
    
    -- 
    	David Pick
    
    
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