Re: [mpls] Question on avoiding TLVs

[Loa Andersson <[e-mail]>]

Haoyu, Tony,

I appreciate the difference in TLVs for the forwarding plane and for the 
control plane.

So looking at the forwarding exactly what should not be TLV encoded?

Can you give examples?

/Loa

On 01/02/2022 01:25, Haoyu Song wrote:
> Hi Tony,
> 
> Yes you are right. Here we are discussing the headers designed for data plane fast path processing.
> Most of the TLVs designed before are for control plane to use.
> But as you see, some current work for supposed fast path processing also suggests to use TLV options (e.g., in IPv6 EH) due to the lack of options. We need to be careful here, because for the parser point of view, each TLV options equals to at least 2 headers.
> Now for MPLS EH, all I suggest is to avoid the issue because we are still at the early stages and have the opportunity to avoid some costly mistakes.
> 
> Best,
> Haoyu
> 
> -----Original Message-----
> From: Tony Li <[e-mail]> On Behalf Of Tony Li
> Sent: Monday, January 31, 2022 9:03 AM
> To: Haoyu Song <[e-mail]>
> Cc: Loa Andersson <[e-mail]>; [e-mail]
> Subject: Re: [mpls] Question on avoiding TLVs
> 
> 
> Haoyu, Loa,
> 
> I think the important point here is that the parsing discussion is focused on the forwarding plane.  TLVs are pervasive in the control plane, where parsing is not a significant cost.
> 
> Tony
> 
> 
>> On Jan 31, 2022, at 8:46 AM, Haoyu Song <[e-mail]> wrote:
>>
>> Hi Loa,
>>
>> Usually TLV is used as a substructure in a header. For sub fields in a header, usually we don't have other choices than using TLV.  But for each header, the type of it is better to be indicated by the previous header to save a parsing state.
>> So all what I say is: as a principle, when designing a header, try not to embed its type in the header itself. Instead, before we get to this header, we should already know its type.
>>
>> Moreover, TLV options in a header also increases the parsing cost. Each fixed size TLV needs two states. Each variable size TLV needs multiple states depending on the size of the option. So another advice is: if it is meant to be processed in hardware, then we should try to limit the use of TLV, and especially variable sized TLV, unless absolutely necessary.
>>
>> Best,
>> Haoyu
>>
>> -----Original Message-----
>> From: Loa Andersson <[e-mail]>
>> Sent: Monday, January 31, 2022 3:27 AM
>> To: [e-mail]; Haoyu Song <[e-mail]>
>> Subject: Question on avoiding TLVs
>>
>> Haoyu,
>>
>> In the slides you uploaded to the "We should try the best to avoid TLV style and variable sized header".
>>
>> MPLS is full of TLVs (LDP, RSVP/TE, LSP Ping, the OAM) are you suggesting we'd change this?
>>
>> Given your advice above what should we do?
>>
>> /Loa
>> -- 
>> Loa Andersson                        email: [e-mail]
>> Senior MPLS Expert                          [e-mail]
>> Bronze Dragon Consulting             phone: [phone]
>> _______________________________________________
>> mpls mailing list
>> [e-mail]
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Fmpls&amp;data=04%7C01%7Chaoyu.song%40futurewei.com%7C232fd182783044649c3e08d9e4db9be9%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C1%7C637792454153079557%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=W6r3NyEsUEcQzpreWqQR5ad4I%2FYRVA%2FJ3QaVqDZRkuo%3D&amp;reserved=0
> 

-- 
Loa Andersson                        email: [e-mail]
Senior MPLS Expert                          [e-mail]
Bronze Dragon Consulting             phone: [phone]