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

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Date:	Tue, 2 Jun 2015 17:33:51 +0100
From:	Robert Shearman <rshearma@...cade.com>
To:	roopa <roopa@...ulusnetworks.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 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.

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.

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.

Thanks,
Rob
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