Date: Thu, 11 Mar 2010 21:32:37 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Qing Li <qingli@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r205024 - head/sys/net Message-ID: <alpine.BSF.2.00.1003112128020.97017@fledge.watson.org> In-Reply-To: <201003111756.o2BHukJu042449@svn.freebsd.org>
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On Thu, 11 Mar 2010, Qing Li wrote:
> The if_tap interface is of IFT_ETHERNET type, but it
> does not set or update the if_link_state variable.
> As such RT_LINK_IS_UP() fails for the if_tap interface.
>
> Also, the RT_LINK_IS_UP() needs to bypass all loopback
> interfaces because loopback interfaces are considered
> up logically as long as the system is running.
>
> This patch fixes the above issues by setting and updating
> the if_link_state variable when the tap interface is
> opened or closed respectively. Similary approach is
> already done in the if_tun device.
A couple of questions:
(1) It used to be the case that quite a few interface drivers and types didn't
have a notion of "link up" -- especially older ethernet devices. Do those
all have the same problem? It was probably a design oversight that
devices don't declare an explicit capability for "can report link state".
(2) While loopback interfaces don't really have a link state, they can be
administratively down -- should/do you check that as well as link state?
And more generally, even if link is up, administratively down should be
obeyed?
Finally, it would be neat if there were a way to have information beyond link
state influence the choice to balance to a particular route/interface. For
example, imagine if I have a router with ECMP, and on the other side on a
single ethernet segment, I have two DSL modems. The ethernet link will remain
up, but I may (via out-of-band mechanisms, such as SNMP or an active probe) be
able to tell that one of the DSL lines is down. Is there a way to push that
information into the kernel currently without deleting the routes, and instead
say "yeah, but for ECMP purposes this is 'down'"?
Robert
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