[dev] Increase the number of MPLS tags in zebra

Jeff Tantsura jefftant at gmail.com
Mon Jul 3 19:50:17 EDT 2017

Hi Olivier,

I’m the author of MSD drafts, let me know if I can help.
Drafts are stable and will go to WGLC after Prague (IETF99), 
My thinking - to keep it simple, only Base MSD has been defined and pre-allocated by IANA, all other types will be defined in another documents.
In most cases, MSD is limited by the underlying HW, obviously SW has to support larger stack too. 
I have discussed an API that could be used to derive MSD value (could be more than 1 by using new MSD type) by querying it with BCM and Barefoot, both agreed on the need to do so.

As I said before - there’s no free lunch in fast path universe,  there’s a price to pay in latency, reduced throughput, number of additional features, etc
Sane limits are healthy and protect a system from abuse.

From implementation prospective - extensions to OSPF/ISIS/BGP-LS are needed to signal MSD, while on x86 platform link MSD doesn’t make much sense, please do implement it for the completeness. 
HW MSD, when available thru an API call should become the node/link MSD, otherwise should be configured under “routing protocol/interface” stanza.

Have you looked into entropy labels yet? 


> On Jul 3, 2017, at 06:13, olivier.dugeon at orange.com wrote:
> Hello,
> This limit must not be avoided. But, fix looking up to what the kernel support.
> In addition, for Segment Routing, there is a new draft (draft-ietf-ospf-segment-routing-msd-05.txt) that could be used to advertise the Maximum Stack Depth. It is on my TODO list for OSPF Segment Routing support in FRR.
> Regards
> Olivier
> Le 03/07/2017 à 14:37, Алексей Болдырев a écrit :
>> By the way, kernel 4.12 is already available: (https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.12.tar.xz <https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.12.tar.xz>)
>> In this kernel, according to the developers, the number of MPLS tags on the stack is 30.
>> Therefore, I suggest that this limit in Zebra should be avoided.
>> https://github.com/FRRouting/frr/issues/776 <https://github.com/FRRouting/frr/issues/776>
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