* how to search for the best route from userspace in netlink?
@ 2019-09-02 22:07 Dave Taht
2019-09-03 3:13 ` David Ahern
0 siblings, 1 reply; 3+ messages in thread
From: Dave Taht @ 2019-09-02 22:07 UTC (permalink / raw)
To: Linux Kernel Network Developers
Windows has the "RtmGetMostSpecificDestination" call:
https://docs.microsoft.com/en-us/windows/win32/rras/search-for-the-best-route
In particular, I wanted to search for the best route, AND pick up the
PMTU from that (if it existed)
for older UDP applications like dnssec[1] and newer ones like QUIC[2].
The alternatives, which
basically include probing perpetually and/or picking really low
values, seem increasingly less than
optimal.
Put in a wrapper around bpf[3]'s lpm calls? Create a new netlink message?
[1] https://github.com/dns-violations/dnsflagday/issues/125
[2] https://tools.ietf.org/html/draft-ietf-quic-transport-22#section-14.1
[3] https://github.com/torvalds/linux/blob/master/kernel/bpf/lpm_trie.c#L164
--
Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-205-9740
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: how to search for the best route from userspace in netlink?
2019-09-02 22:07 how to search for the best route from userspace in netlink? Dave Taht
@ 2019-09-03 3:13 ` David Ahern
2019-09-03 9:29 ` Dave Taht
0 siblings, 1 reply; 3+ messages in thread
From: David Ahern @ 2019-09-03 3:13 UTC (permalink / raw)
To: Dave Taht, Linux Kernel Network Developers
On 9/2/19 4:07 PM, Dave Taht wrote:
> Windows has the "RtmGetMostSpecificDestination" call:
> https://docs.microsoft.com/en-us/windows/win32/rras/search-for-the-best-route
>
> In particular, I wanted to search for the best route, AND pick up the
> PMTU from that (if it existed)
> for older UDP applications like dnssec[1] and newer ones like QUIC[2].
RTM_GETROUTE with data for the route lookup. See iproute2 code as an
example.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: how to search for the best route from userspace in netlink?
2019-09-03 3:13 ` David Ahern
@ 2019-09-03 9:29 ` Dave Taht
0 siblings, 0 replies; 3+ messages in thread
From: Dave Taht @ 2019-09-03 9:29 UTC (permalink / raw)
To: David Ahern; +Cc: Linux Kernel Network Developers
On Mon, Sep 2, 2019 at 8:13 PM David Ahern <dsahern@gmail.com> wrote:
>
> On 9/2/19 4:07 PM, Dave Taht wrote:
> > Windows has the "RtmGetMostSpecificDestination" call:
> > https://docs.microsoft.com/en-us/windows/win32/rras/search-for-the-best-route
> >
> > In particular, I wanted to search for the best route, AND pick up the
> > PMTU from that (if it existed)
> > for older UDP applications like dnssec[1] and newer ones like QUIC[2].
>
> RTM_GETROUTE with data for the route lookup. See iproute2 code as an
> example.
Yes. I really didn't describe my thinking very well. It's coping with
pmtu better
in the case of a more increasingly udp'd and tunneled internet. tcp
(being kernel based)
will do the probe and cache that attribute of the path, udp does not.
A udp based app with root privs could be setting it after figuring it
out, a userspace one cannot.
for more detail from server-al sides of that philosophical debate,
please see the links I posted
originally.
--
Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-205-9740
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-09-02 22:07 how to search for the best route from userspace in netlink? Dave Taht
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