[Qemu-devel] Re: weird slirp problems (dns lookups stopped working, and maybe more)

[Juergen Lock]

On Tue, Jan 09, 2007 at 09:47:40PM +0100, Juergen Lock wrote:
> Hi!
> 
>  I'm not sure why I didn't notice signs of this earlier (using the
> Dec 25 snapshot, I'm on FreeBSD), maybe I really only talked to the host
> (10.0.2.2) from inside guests.  Anyway, after I first saw it yesterday
> night, today I sniffed on the external interface and saw dns requests
> of a `host google.com' going out to 224.0.0.251, port 5353, instead
> of the dns in resolv.conf.  [...]

>  In between I see these which I'm not sure where they are coming from:
> 
>  ...
> m_get...
>  m = 9bd7800
> ip_input...
>  m = 9bd7800
>  m_len = 74
> udp_input...
>  m = 9bd7800
>  iphlen = 20
>  udp_input(), ip_dst.s_addr=0xe00000fb, uh_dport=5353
> sosendto...
>  so = 9b39b80
>  m = 9bd7800
>  sendto()ing, addr.sin_port=5353, addr.sin_addr.s_addr=224.0.0.251
> m_free...
>  m = 9bd7000
> ip_slowtimo...
> tcp_slowtimo...
>  ...

Ok, garrison on irc just helped solve this mystery:  This (the same)
one actually goes out first, before the 10.0.2.3 one (I didn't notice
at first), and since slirp reuses the socket because the source ip and
port hasnt changed (slirp/udp.c lines 172 and up, it doesn't check the
dest ip), the second packet with the 10.0.2.3 dest ip (which gets
replaced with the hosts's dns) goes out wrong.  And the reason this
worked previously with the same guest is multicast started working
only recently...

 (Now why tcp stopped working for the other guy I still don't know...)

 Thanx,
        Juergen