Subject: kern/28716: Turning off cksum fails localhost ipv4 udp request (named in my case)
To: None <kern-bug-people@netbsd.org, gnats-admin@netbsd.org,>
From: Markus W Kilbinger <kilbi@rad.rwth-aachen.de>
List: netbsd-bugs
Date: 12/19/2004 22:09:00 
>Number:         28716
>Category:       kern
>Synopsis:       Turning off cksum fails localhost ipv4 udp request (named in my case)
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Dec 19 22:09:00 +0000 2004
>Originator:     kilbi@rad.rwth-aachen.de
>Release:        NetBSD 2.99.11
>Organization:
>Environment:
	
	
System: NetBSD qube 2.99.11 NetBSD 2.99.11 (QUBE) #0: Sun Dec 19 20:10:15 MET 2004  kilbi@qie:/sys/arch/cobalt/compile/QUBE cobalt
Architecture: mipsel
Machine: cobalt
>Description:
	Recent -current changes to turn off lo0 cksum

		http://news.gw.com/netbsd.source.changes/169185

	make udp ipv4 requests to localhost fail (run into timeout).

	Turning on lo0 cksum for udp

		sysctl -w net.inet.udp.do_loopback_cksum=1

	makes ipv4 udp requests work again.
>How-To-Repeat:
	I ran into this problem while observing my localhost's dns
	server not answering requests via ipv4 from localhost itself.
	ipv6 udp request to my localhost's dns server work fine with
	'net.inet6.udp6.do_loopback_cksum = 0'.
>Fix:
	Workaround would be 'sysctl -w net.inet.udp.do_loopback_cksum=1'.

>Unformatted: