netdev - Re: [RFC net-next 3/3] mpls: new ipmpls device for encapsulating IP packets as mpls

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Message-ID: <556DFC91.1090708@cumulusnetworks.com>
Date:	Tue, 02 Jun 2015 11:57:21 -0700
From:	roopa <roopa@...ulusnetworks.com>
To:	Robert Shearman <rshearma@...cade.com>
CC:	netdev@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Graf <tgraf@...g.ch>,
	Dinesh Dutt <ddutt@...ulusnetworks.com>,
	Vivek Venkatraman <vivek@...ulusnetworks.com>
Subject: Re: [RFC net-next 3/3] mpls: new ipmpls device for encapsulating
 IP packets as mpls

On 6/2/15, 9:33 AM, Robert Shearman wrote:
> On 02/06/15 17:15, roopa wrote:
>> On 6/1/15, 9:46 AM, Robert Shearman wrote:
>>> Allow creating an mpls device for the purposes of encapsulating IP
>>> packets with:
>>>
>>>    ip link add type ipmpls
>>>
>>> This device defines its per-nexthop encapsulation data as a stack of
>>> labels, in the same format as for RTA_NEWST. It uses the encap data
>>> which will have been stored in the IP route to encapsulate the packet
>>> with that stack of labels, with the last label corresponding to a
>>> local label that defines how the packet will be sent out. The device
>>> sends packets over loopback to the local MPLS forwarding logic which
>>> performs all of the work.
>>>
>>>
>> Maybe a silly question, but when you loop the packet back, what does the
>> local MPLS forwarding logic
>> lookup with ? It probably assumes there is a mpls route with that label
>> and nexthop.
>> Will this need any internal labels (thinking same label stack different
>> tunnel device etc) ?
>
> Yes, it requires that local/internal labels have been allocated and 
> label routes installed in the label table for them.
This is our only concern.
>
> It is entirely possible to put the outgoing interface into the encap 
> data to avoid having to allocate extra labels, 
> but I did it this way in order to support PIC Core for MPLS-VPN routes.

hmm..., is a netdevice must in this case.., can you please elaborate on 
this ?.

>
> Note: I have two extra patches which avoid using the loopback device 
> (which causes the TTL to end up being one less than it should on 
> output), but I haven't posted them here because they were dependent on 
> other mpls changes in my tree.

ok, thanks.

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