kern/76966: udp/520 reply packets when routed is not running

Emil Cazamir emil.cazamir at
Mon Feb 7 02:50:21 PST 2005

The following reply was made to PR kern/76966; it has been noted by GNATS.

From: "Emil Cazamir" <emil.cazamir at>
To: <dwmalone at>
Cc: <FreeBSD-gnats-submit at>
Subject: RE: kern/76966: udp/520 reply packets when routed is not running
Date: Mon, 7 Feb 2005 12:53:08 +0200

 -----Original Message-----
 From: dwmalone at [mailto:dwmalone at] 
 Sent: 6 februarie 2005 19:41
 To: Emil Cazamir
 Cc: FreeBSD-gnats-submit at
 Subject: Re: kern/76966: udp/520 reply packets when routed is not running
 On Tue, Feb 01, 2005 at 05:35:28PM +0200, Emil Cazamir wrote:
 > >Description:
 > 	The FreeBSD kernel seems to respond to udp/520 packets even when
 > there is no such daemon running.
 There's no code in the FreeBSD kernel for doing this, however I think
 I know what is going on...
 > 17:03:32.185977 0:f:3d:47:8b:de ff:ff:ff:ff:ff:ff 0800 60:
 > >  RIPv1-resp [items 0]: (DF)
 > 17:03:32.186153 0:0:0:0:0:2 0:0:0:0:0:1 0800 60: >
 >  RIPv1-resp [items 0]: (DF)
 Your FreeBSD maching gets a packet for - I suspect
 you have the netmask on your FreeBSD machine set incorrectly so it
 does not consider this a broadcast address. Consequently, it probably
 considers this a misdirected packet and so sends an ICMP redirect
 and then forwards the packet, in this case to the default router.
 I'm not sure why the source address on the packet has changed -
 that bit seems a bit odd.
 There is no problem with the netmask, there are several subnets sharing the
 same wire. I lokked into few kernel config files and I didn't found anything
 specific. I think that the cause of what's happening is somewhere in
 natd/libalias, all the machines which respond to [or  forward] udp/520
 packets are running natd. I will make available kernel config files, process
 listings, etc if it is required.

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