[PATCH] Netlink: add krt_scope attribute

[Ondrej Zajicek]

On Thu, Sep 15, 2016 at 06:05:27PM +0200, Vincent Bernat wrote:
> The general-purpose scope attribute is detailed in the documentation as
> an attribute that BIRD won't set and won't use. Therefore, to expose the
> scope of a kernel route, this commit adds a new attribute,
> krt_scope. Its possible values are the numeric values for SCOPE_*
> variables (1 is SCOPE_LINK for example), not the values from the
> kernel (253 is RT_SCOPE_LINK). Both import and export are supported.

Hi

Thans for the patch. I agree that we should handle the attribute
if it has some usage. I have some questions/comments:

Perhaps we should use the same approach like we use for krt_realm?
i.e., handle krt_scope as an integer variable and import constants
from /etc/iproute2/rt_scopes. So we could handle all values as the
Linux kernel and we would be consistent with iproute2 tools.

I don't really understand how Linux handles scope argument. If i
remember correctly, the idea is that next hop of a route could be
resolvable through a route with higher scope value, but it seems
that it distinguish only host (internal), link and anything other.

> A typical use case is to install "scope link" routes for directly
> connected destinations, as the kernel won't accept routes with a broader
> scope when issuing an internal lookup.

You mean for regular routes (with next hop) or device routes?

I though that kernel sets scope link automatically for device routes,
but in reality it is done by ip tool. Perhaps we should do that too.

I could create regular routes with scope link directed to device routes
with scope link (which is a bit strange) and then create regular routes
with normal scope directed on them, but i cannot get more hierarchy.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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