Date: Wed, 14 Mar 2007 16:00:13 +0000 From: "Bruce M. Simpson" <bms@FreeBSD.org> To: Gleb Smirnoff <glebius@FreeBSD.org>, freebsd-net@FreeBSD.org, Vladimir Ivanov <wawa@yandex-team.ru>, bug-followup@FreeBSD.org Subject: Re: kern/106722: [net] [patch] ifconfig may not connect an interface to known network Message-ID: <45F81C0D.2000608@FreeBSD.org> In-Reply-To: <20070314115916.GB2713@cell.sick.ru> References: <20070314115916.GB2713@cell.sick.ru>
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Gleb Smirnoff wrote:
> AFAIK, the problem needs a more generic approach. I see two approaches.
>
> 1) Introduce RTM_CHANGEADD, a command that will forcibly add route,
> deleting all conflicting ones. Use this command in in_addprefix().
>
> 2) In rt_flags field we still have several extra bits. We can use
> them to specify route source - RTS_CONNECTED, RTS_STATIC, RTS_XXX,
> where XXX is a routing protocol. When issuing RTM_ADD a route with
> a preferred source (e.g. CONNECTED vs STATIC) will override the old
> one.
>
>
The proposed changes also constitute a hack.
I understand that they are being proposed to address problems we
currently have in the stack, i.e. that we do not support multipathing,
though it is more than likely they will be blown away in future when the
architecture changes (and it has to change).
Approach 1 is largely irrelevant if multiple paths are introduced to the
network stack; there is then no concept of a conflicting forwarding
entry, only preference derived from the interface, entry flags, or the
entry ('route') itself.
Approach 2 has some merit to it, although the forwarding plane should
not care where the forwarding entry came from unless it needs to (e.g.
next-hop resolution).
It seems reasonable that the forwarding plane should tag entries as
being 'CONNECTED' i.e. derived from the address configuration of an
interface. I believe many implementations out there do this, and
multi-path does not change this.
We already have the RTF_PROTO1 flag to determine if the forwarding entry
('route') came from a routing protocol in userland, so there should be
no need to change the existing flags.
The RTF_STATIC flag only has special meaning in that it means 'the user
added this forwarding entry manually via the route(8) command'. We
should preserve these semantics, though I believe we should start
implementing forwarding preference in the radix trie.
I think it seems acceptable and reasonable that we use a limited form of
Approach 2 to clobber 'routes' being aded in the case described in the
PR, until such time as the network stack is re-engineered to support
multiple paths and forwarding preference.
I also believe it is useful if we start to use more modern technical
jargon to discuss 'routes' in the network stack, because we are actually
discussing the behaviour of entries in a forwarding table.
Regards,
BMS
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