Re: Odd routing problem

From: Per Hedeland (per_at_hedeland.org)
Date: 02/26/05 

Date: Sat, 26 Feb 2005 00:36:26 +0000 (UTC)

In article <PEETd.216$h53.152@newsfe4-gui.ntli.net> Mike Scott
<usenet.9@spam.stopper.scottsonline.org.uk> writes:
>I've a small LAN at home - a fbsd gateway with 3 NICS - rl0 connected to
>a cable modem, dc0 to the net 192.168.0 and xl0 to 192.168.1 -- xl0 in
>practice serves only the wireless connection for my son. Other machines
>are windows, mainly. I'm using ipf on the gateway to control access,
>but this hasn't been changed for a while. All was working well, until
>Son lost his internet priv's, enforced by 'ifconfig xl0 down'.
>
>On trying to restore the connection a day later (ifconfig xl0 up), I
>found problems. In particular, broadcast ntp udp packets for 192.168.1
>are now being wrongly sent to rl0, and blocked by the firewall. The
>routing table looks OK; I can ping both wireless access point and bridge
>on this net. I can't see why udp port 123 should go astray like this.

Hm, are you seeing anything *other* than ntp packets going astray? I
suspect that the problem is with ntpd rather than with your routing, in
particular if ntpd was restarted while xl0 was down and hasn't been
restarted since it was brought up again. Ntpd does a lot of special
stuff with interfaces, mostly visible through the fact that it will bind
one UDP socket to port 123 for each interface address (plus one for the
wildcard).

This is done so it can respond to queries with the appropriate source
address, but it also needs to worry about what the appropriate broadcast
address is for the respective interfaces. If it didn't find xl0 up when
it started, but you have specified that it should send broadcasts with
the xl0 broadcast address, I wouldn't be surprised if it sent them as
unicasts instead. Not sure why they would go out the wrong interface
though, but the cause is probably related somehow... Try restarting ntpd
and see if the problem goes away.

--Per Hedeland
per@hedeland.org

Relevant Pages

  • Re: Odd routing problem
    ... broadcast ntp udp packets for 192.168.1 ... > particular if ntpd was restarted while xl0 was down and hasn't been ... Not sure why they would go out the wrong interface ...
    (comp.unix.bsd.freebsd.misc)
  • Re: single host netmask (255.255.255.255)
    ... The routes from three interfaces, propagate via OSPF to the rest of network.... ... One way is to remember IP addresses assigned to each interfaces, but more smart solution is to assign to this machine one EXTERNAL LOOPBACK address (single IP with mask 255.255.255.255, in other words SINGLE HOST assigned to Microsoft loopback adapter), and propagate this address ... The address 255.255.255.255 denotes a broadcast on a local hardware network, ...
    (microsoft.public.win2000.networking)
  • Re: how to disallow nis-client to broadcast on certain interfaces
    ... Did you look at implementing NIS securnets by using the file ... how to disallow nis-client to broadcast on certain interfaces ...
    (AIX-L)
  • routes disappear
    ... netstat to report no routes. ... the latest box to do this has two interfaces (this one has tg3 interfaces, ... full duplex. ... code 1 error to a broadcast: ...
    (Linux-Kernel)
  • Re: a few questions about broadcast
    ... I tried to have on the client in addition to the "broadcastclient" ... ntpd stability, precision, or accuracy. ... > servers on the subnet even though only 2 servers broadcast, ...
    (comp.protocols.time.ntp)