Re: Is traceroute supposed to work in user mode networking (slirp) ?

[Kai Peter]

Just stumbled over this:

Note - if you are using the (default) SLiRP user networking, then ping 
(ICMP) will not work, though TCP and UDP will. Don't try to use ping to 
test your QEMU network configuration!

(https://wiki.qemu.org/Documentation/Networking)



On 2020-07-09 14:18, Ottavio Caruso wrote:
> Hi,
>
> I have enabled pinging from the guest changing the
> "net.ipv4.ping_group_range" on my Linux host. I can now ping any host
> using icmp. But I cannot get  traceroute to work with standard udp:
>
> $ traceroute 8.8.8.8
> traceroute to 8.8.8.8 (8.8.8.8), 64 hops max, 40 byte packets
>  1  * * *
>  2  * * *
>  3  * * *
>  4  * * *
> [and so on]
>
> And if I use traceroute over icmp, I only get one hop shown:
>
> $ traceroute -I 8.8.8.8
> traceroute to 8.8.8.8 (8.8.8.8), 64 hops max, 60 byte packets
>  1  dns.google (8.8.8.8)  26.147 ms  27.88 ms  20.048 ms
>
> I have tested this with various guest OSes (OpenBSD, FreeBSD, NetBSD,
> Small Damn Linux).
>
> I've played around with various virtual interfaces but I have the same 
> result.
>
> Any clues? Is this intended behaviour? ANy workarounds that don't
> involve tap/tun/bridges?
>
> --
> Ottavio Caruso

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