Date: Mon, 20 Mar 2000 11:03:07 -0800 (PST) From: Archie Cobbs <archie@whistle.com> To: wollman@khavrinen.lcs.mit.edu (Garrett Wollman) Cc: freebsd-current@FreeBSD.ORG Subject: Re: ICMP socket weirdness Message-ID: <200003201903.LAA05714@bubba.whistle.com> In-Reply-To: <200003181954.OAA77677@khavrinen.lcs.mit.edu> from Garrett Wollman at "Mar 18, 2000 02:54:26 pm"
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Garrett Wollman writes: > > When the program is run, if you ping the IP address from the > > local machine, it sees packets. However, if you ping it from > > a remote machine, it doesn't see packets. > > The ICMP never passes certain packets up to raw listeners. These > include ECHO REQUEST, TIMESTAMP REQUEST, and SUBNET MASK REQUEST > packets -- but not the corresponding replies! So, when you ping the > local machine, you will see the ECHO REPLY packets on all raw > listners, but not the initial ECHO REQUESTs. When you ping from a > remote machine, you never see the ECHO REQUEST packets because the > kernel takes care of them, and you never see the ECHO REPLY packets > because they are addressed to the other machine. Is this a FreeBSD-specific thing, or to other UNIX's have this same peculiar behavior? > It would be possible to pass all ICMP packets to the raw listeners, > but it would require rewriting parts of icmp_input() (which would not > be a bad idea) either to avoid modifying the packet in-place or to > keep a copy of the original before responding -- either of which would > slow down `ping' processing. The existence of m_dup() makes the latter option a lot easier.. -Archie ___________________________________________________________________________ Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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