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

[Ottavio Caruso]

On Sun, 19 Jul 2020 at 03:50, Samuel Thibault <samuel.thibault@gnu.org> wrote:
>
> Hello,
>
> Ottavio Caruso, le mar. 14 juil. 2020 12:15:48 +0100, a ecrit:
> > I cannot get traceroute to work with standard udp from any of my
> > guests.
> >
> > $ traceroute 8.8.8.8
> > traceroute to 8.8.8.8 (8.8.8.8), 64 hops max, 40 byte packets
> >  1  * * *
>
> That was because
>
> - libslirp was not forwarding the ttl value, thus always set to 64 hops
> - libslirp was not reporting icmp errors.
>
> I had a try at both, and that indeed seems to be fixing the issue:
> https://gitlab.freedesktop.org/slirp/libslirp/-/merge_requests/48
> https://gitlab.freedesktop.org/slirp/libslirp/-/merge_requests/49
>
> > Any clues? Is this intended behaviour? Any workarounds that don't
> > involve tap/tun/bridges?
>
> Not without updating libslirp with the abovementioned patches.

Thanks Samuel. I've added a comment on the portal, but for the benefit
of qemu-devel:

Applying this patch on the latest qemu (5.0.90), does indeed implement
traceroute, but it only reports one hop. I've tested this on a FreeBSD
guest and a minimal DSL Linux guest:

root@FreeBSD:/home/oc # uname -sr
FreeBSD 12.1-RELEASE-p5
root@FreeBSD:/home/oc # traceroute google.com
traceroute to google.com (216.58.206.110), 64 hops max, 40 byte packets
 1  lhr25s14-in-f14.1e100.net (216.58.206.110)  20.555 ms  19.981 ms  19.042 ms
root@FreeBSD:/home/oc # traceroute 1.1.1.1
traceroute to 1.1.1.1 (1.1.1.1), 64 hops max, 40 byte packets
 1  one.one.one.one (1.1.1.1)  19.722 ms  19.171 ms  19.018 ms



-- 
Ottavio Caruso