Snort mailing list archives
RE: Alerts of the ICMP relationship with smtp connection?
From: "Briggs, Bruce" <Bruce.Briggs () suny edu>
Date: Tue, 07 Jun 2005 17:03:27 -0400
The DF bit indicates that anything transferring the packet, such as a router, is not allowed to fragment the packet into smaller chucks to get it to it's destination. This could be done by PMTU checking, but the packet size is quite small for PMTU. I'm not sure why your server is sending these out. It looks like you have 3 rules which are logging 1 ping packet. Either that or the packet is being sent 3 times with identical info. Bruce -----Original Message----- From: Paulo [mailto:listassec () yahoo com] Sent: Tuesday, June 07, 2005 10:17 AM To: Briggs, Bruce; Bob Konigsberg Cc: Snort.org List Subject: RE: [Snort-users] Alerts of the ICMP relationship with smtp connection? Hi Bruce, Thanks by help. Below is the snort alerts. Where 200.201.202.203 is the IP address of the destination from mail. And 200.201.101.102 is my IP Address. [**] [1:366:7] ICMP PING *NIX [**] [Classification: Misc activity] [Priority: 3] 05/18-10:27:22.866164 200.201.202.203 -> 200.201.101.102 ICMP TTL:54 TOS:0x0 ID:1 IpLen:20 DgmLen:84 DF Type:8 Code:0 ID:31252 Seq:1 ECHO [**] [1:384:5] ICMP PING [**] [Classification: Misc activity] [Priority: 3] 05/18-10:27:22.866164 200.201.202.203 -> 200.201.101.102 ICMP TTL:54 TOS:0x0 ID:1 IpLen:20 DgmLen:84 DF Type:8 Code:0 ID:31252 Seq:1 ECHO [**] [1:368:6] ICMP PING BSDtype [**] [Classification: Misc activity] [Priority: 3] 05/18-10:27:23.865467 200.201.202.203 -> 200.201.101.102 ICMP TTL:54 TOS:0x0 ID:2 IpLen:20 DgmLen:84 DF Type:8 Code:0 ID:31252 Seq:2 ECHO [Xref => http://www.whitehats.com/info/IDS152] The icmp packet is small and the flag DF is set on. I was seeing the tcp packet size that my postfix sends and it's with 1500 bytes of size. The DF flag in icmp packet, mean that the destination mail server is telling the postfix doesn´t fragment packet? Normally, the mails sends are with CorelDraw files attachments, almost already with 1 Mb or more. Thanks by help again. --- "Briggs, Bruce" <Bruce.Briggs () suny edu> wrote:
Since these are echo request (ping) ICMP packets, they are not likely to be caused by PMTU checking. However, some server do a ping prior to sending, to make sure that the far end is up. You need to inspect the ICMP packet to see if it is a big (near 1500 bytes) or small packet, if the do not fragment bit is set, etc. to try to ascertain why this may be sent by the sending software. Perhaps you should as the software provider why it sends out ICMP packets. Bruce -----Original Message----- From: snort-users-admin () lists sourceforge net [mailto:snort-users-admin () lists sourceforge net] On Behalf Of Paulo Sent: Tuesday, June 07, 2005 7:59 AM To: Bob Konigsberg Cc: Snort.org List Subject: RE: [Snort-users] Alerts of the ICMP relationship with smtp connection? Hi Bob, Thanks by help. The message below is my original message. After this message, I have searching an answer to this question. In a test, I was seeing the maillog of the postfix while the postfix sends the mail. Together i was seeing the alert log of the Snort too. The alerts on snort are generated exactly while the postfix sends mails. The files that I was seeing is /var/log/maillog and /var/log/snort/alert. I think that the alerts are harmless traffic, but i'd like to understand why it's generated. Thanks by help again. ORIGINAL MESSAGE: I am using Snort version Version 2.3.2 (Build 12). I have in my snort logs the alerts: 366 - ICMP Ping *nix 384 - ICMP Ping 368 - Ping BSDtype I investigated my others systems logs and in the time that this alert is recorded is the same that registered smtp connection in the maillog arquive from my postfix server. The source IP address in snort's log is equal the destination IP address in the maillog to smtp connection. This alerts can to be generated by my mail server when it sends mails? This alerts is a false positive? Thanks by help --- Bob Konigsberg <bobkberg () networkeval com> wrote:ICMP type 8 is an echo request - someone is trying to ping you - probably in an attempt to map out your network. Bob -----Original Message----- From: snort-users-admin () lists sourceforge net [mailto:snort-users-admin () lists sourceforge net]OnBehalf Of Paulo Sent: Monday, June 06, 2005 12:51 PM To: Frank Knobbe Cc: Snort.org List Subject: Re: [Snort-users] Alerts of the ICMP relationship with smtp connection? Thanks Frank, How can I to confirm this? The alerts are ICMPtype8. Thanks by help again. --- Frank Knobbe <frank () knobbe us> wrote:On Mon, 2005-05-30 at 13:40 -0700, Paulo wrote:I didn't solve this yet. Please, anyone canhelpme? Maybe you didn't get responses because it's notaSnort related issue.To answer your question, read up on Path MaximumTransmit Unit (PMTU)Discovery by googling it. Here a couple linksthatGoogle spit outright away. http://www.netheaven.com/pmtu.html which also references ftp://ftp.rfc-editor.org/in-notes/rfc1191.txt While you are learning about PTMU, please reviewyour firewall ruleset and make sure you don't block ALL inboundICMPpackets. Please letat least type 3 and type 11 ICMP packetsthrough.(Hint: The remote mail servers are sending alargeICMP packet inorder to discover the MTU between them and you.Itis harmlesstraffic.) Hope that helps, Frank__________________________________ Discover Yahoo! Find restaurants, movies, travel and more fun for the weekend. Check it out! http://discover.yahoo.com/weekend.html
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Current thread:
- Alerts of the ICMP relationship with smtp connection? Paulo (May 24)
- Re: Alerts of the ICMP relationship with smtp connection? Matt Jonkman (May 24)
- <Possible follow-ups>
- Re: Alerts of the ICMP relationship with smtp connection? Paulo (May 24)
- Re: Alerts of the ICMP relationship with smtp connection? Paulo (May 30)
- Re: Alerts of the ICMP relationship with smtp connection? Frank Knobbe (May 31)
- Re: Alerts of the ICMP relationship with smtp connection? Paulo (Jun 06)
- Re: Alerts of the ICMP relationship with smtp connection? Frank Knobbe (May 31)
- RE: Alerts of the ICMP relationship with smtp connection? Paulo (Jun 07)
- RE: Alerts of the ICMP relationship with smtp connection? Briggs, Bruce (Jun 07)
- RE: Alerts of the ICMP relationship with smtp connection? Paulo (Jun 07)
- RE: Alerts of the ICMP relationship with smtp connection? Briggs, Bruce (Jun 07)
- Snort Inline again.... Xavier Cabrera (Jun 07)
- RE: Alerts of the ICMP relationship with smtp connection? Paulo (Jun 08)
- RE: Alerts of the ICMP relationship with smtp connection? Paulo (Jun 10)