Date: Tue, 5 Jun 2001 18:30:14 +0200 (CEST) From: Andre Albsmeier <andre.albsmeier@mchp.siemens.de> To: FreeBSD-gnats-submit@freebsd.org Subject: kern/27890: FreeBSD not always seems to take the best route Message-ID: <200106051630.f55GUEt76616@curry.mchp.siemens.de>
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>Number: 27890
>Category: kern
>Synopsis: FreeBSD not always seems to take the best route
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jun 05 09:40:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Andre Albsmeier
>Release: FreeBSD 4.3-STABLE i386
>Organization:
>Environment:
System: 4.3-STABLE #67: Fri Jun 1 12:49:52 CEST 2001
>Description:
I have observed this behaviour for a long time now but finally had
time to dig into it... I reference syslogd as an example here
but I think the problem lies in the network code of the kernel...
Simple network:
- two routers (1 and 2)
- host C with IP 192.168.1.3
- host S with IP 192.168.2.1
All machines are FreeBSD 4.3-STABLE.
Router 1 routes pkts between the Internet and 192.168.1.0
Router 2 routes pkts between 192.168.1.0 and 192.168.2.0
+-----+ +-----+
default | | 192.168.1.0 | | 192.168.2.0
-----------| 1 |--------+--------| 2 |--------+-------- more hosts
| | | | | |
+-----+ | +-----+ |
| |
+-----+ +-----+
| | | |
192.168.1.3 | C | | S | 192.168.2.1
| | | |
+-----+ +-----+
Relevant parts of netstat -rn on C during normal operation:
-------------------------------------------------------------
Destination Gateway Flags Netif Expire
default 192.168.1.1 UGSc fxp0
127.0.0.1 127.0.0.1 UH lo0
192.168.1 link#1 UC fxp0 =>
192.168.1.1 0:e0:18:90:91:bb UHLW fxp0 1182
192.168.1.2 0:e0:18:90:94:c8 UHLW fxp0 1058
192.168.1.3 0:e0:18:90:45:dc UHLW lo0
192.168.1.255 ff:ff:ff:ff:ff:ff UHLWb fxp0
192.168.2 192.168.1.2 UGc fxp0
The syslogd on host C is configured to log messages
to syslogd running on host S. This works perfectly,
all messages appear on host S.
Now we delete the route to net 192.168.2.0 on host C (this
can appear automatically if router 2 and/or its routed go
down for a while). If syslogd now wants to send a message
to S, the kernel uses the default route which is obvious
because the route to net 192.168.2.0 is gone. We can see the
packets go into router 1. I consider this as the correct
behaviour as well.
Now we bring back the route to net 192.168.2.0 again on host
C exactly as it was before (e.g. by restarting router 2 and/or
its routed). We can verify this with netstat -rn on C. We can
also ping host S or telnet to it or do other stuff which all
work perfectly.
The problem is that each time when syslogd on C wants to send
a packet to S, the kernel still uses 1 as router even though
it should send them through 2. After HUPing or restarting
syslogd on C (which means that the UDP socket is closed and
opened again) things are back to normal.
It seems that as long as packets can be send somewhere, the
kernel doesn't bother if there is a better route to the
destination until the socket is closed and opened again.
>How-To-Repeat:
See above.
>Fix:
Unknown. I am happy to test suggestions, of course.
>Release-Note:
>Audit-Trail:
>Unformatted:
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