RE: ICMP Destination Unreachable (Communication Administratively Prohibited)

["Ofir Arkin" <ofir () sys-security com>]

Dushyanth,

The Error message indicates that the destination system is configured to
reject datagrams from the sending system. This error is used when
datagrams based on some sort of criteria are being filtered by a
filtering device (firewall/router/other filtering devices) restrictions
or other security measures.

We can conclude that our Destination Host might be up and running, but
we cannot reach it, since the filtering device is blocking our packets,
and is instructing us to stop sending datagrams.

With the next example a router is configured to block all requests,
coming from the Internet, targeting port 53 on the destination machine
it applies its ACL on:

05/09/01-12:29:41.399543 RoutersIP -> SourceIP 
ICMP TTL:244 TOS:0x0 ID:24442 IpLen:20 DgmLen:56 
Type:3 Code:13 DESTINATION UNREACHABLE: PACKET FILTERED 
** ORIGINAL DATAGRAM DUMP: 
SourceIP:4667 -> DestinationIP:53 
TCP TTL:53 TOS:0x0 ID:40019 IpLen:20 DgmLen:60 
**U****F Seq: 0x97EABAF6 Ack: 0x1C1D1E1F Win: 0x2223 TcpLen: 8 
UrgPtr: 0x2627 
** END OF DUMP 
00 00 00 00 45 00 00 3C 9C 53 40 00 35 06 29 B0 ....E..<.S@.5.). 
xx xx xx xx yy yy yy yy 12 3B 00 35 97 EA BA F6 .....Z...;.5....


For more information please see "ICMP Usage In Scanning" Chapter 2 page
20, 52-53. Available from
http://www.sys-security.com/html/projects/icmp.html. 


Regarding your example, these systems report that communication from
your system was not able to reach its destination because a filtering
device blocked your packets.

If you had put the complete trace we would be able to tell what
communication exactly caused this error message to be trigger.


Ofir Arkin [ofir () sys-security com]
Founder
The Sys-Security Group
http://www.sys-security.com
PGP CC2C BE53 12C6 C9F2 87B1 B8C6 0DFA CF2D D360 43FA


-----Original Message-----
From: snort-users-admin () lists sourceforge net
[mailto:snort-users-admin () lists sourceforge net] On Behalf Of Dushyanth
Harinath
Sent: ש 25 אוגוסט 2001 9:19
To: snort-users () lists sourceforge net
Subject: [Snort-users] ICMP Destination Unreachable (Communication
Administratively Prohibited)

Hi guys,
Iam new to snort and have a little bit of networking knowledge.

I have installed snort in my server with snortdb support aand i have
also
installed snortreport.Snort is working fine .I have this snort alert's
from
more that 10 source ip's targetting machine on my network.The exact
message is.

ICMP Destination Unreachable (Communication Administratively Prohibited)

CID:1 [**] ICMP Destination Unreachable (Communication Administratively
Prohibited) [**]
2001-08-21 17:06:51 157.130.91.86 -> 203.115.120.210
ICMP TTL:243 TOS:0x0 ID:51765 IPLen: DgmLen:56 HLen:5 CSumIP:0xC070
Type:3 Code:13 ID: Seq:

This is just one such alert .I have got 12 alerts from different ip's in
the
last 12 hrs and above 48 in the last 30 days.

I know i can disable this alert by commenting out the line in
icmp.rules.But
iam not sure what this means.

I will be glad to RTFM or will someone please enlighten me about this.

Best regards
dushyanth

-- 
My computer, my documents, my briefcase, my ASS! 

Dushyanth Harinath
Programmer/Sys Admin
Archean Infotech Limited
Ph No:091-040-3228666,6570704,3228674
http://www.archeanit.com



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