Subject: [OSPF] OSPF Link Overload (aka, Graceful Link Shutdown) MAX-TE-METRIC

From: "Acee Lindem (acee)" <[email-masked]>
Date: Wed, 10 Jan 2018 02:21:08 +0000

Hi Shraddha,

We noticed that RFC 5817 sets the TE Metric to 0xffffffff for graceful TE shutdown and the OSPF Link Overload draft uses MAX-TE-METRIC (0xfffffffe). Two Questions:

   1. MAX-TE-METRIC is being defined in the OSPF Link Overload draft – correct? It is not a reference from some other RFC or draft?
   2. Why not just use 0xffffffff like RFC 5817?

Thanks,
Acee

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From: Shraddha Hegde <[email-masked]>
Date: Fri, 12 Jan 2018 08:07:24 +0000

Acee,

Pls see inline..

From: Acee Lindem (acee) [mailto:[email-masked]]
Sent: Wednesday, January 10, 2018 7:51 AM
To: Shraddha Hegde <[email-masked]>
Cc: OSPF WG List <[email-masked]>
Subject: OSPF Link Overload (aka, Graceful Link Shutdown) MAX-TE-METRIC

Hi Shraddha,

<Shraddha>Yes. This value is introduced in this draft.

The reason was that some implementation treat te-metric 0xffffffff as invalid value and do not setup paths through them. Using 0xffffffff-1 seemed like a safe option

<Shraddha>We can if we have the Working Group Consensus.

Thanks,
Acee

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From: "Acee Lindem (acee)" <[email-masked]>
Date: Fri, 12 Jan 2018 14:40:16 +0000

Hi Shraddha,

From: Shraddha Hegde <[email-masked]<mailto:[email-masked]>>
Date: Friday, January 12, 2018 at 3:07 AM
To: Acee Lindem <[email-masked]<mailto:[email-masked]>>
Cc: OSPF WG List <[email-masked]<mailto:[email-masked]>>
Subject: RE: OSPF Link Overload (aka, Graceful Link Shutdown) MAX-TE-METRIC

Acee,

Pls see inline..

From: Acee Lindem (acee) [mailto:[email-masked]]
Sent: Wednesday, January 10, 2018 7:51 AM
To: Shraddha Hegde <[email-masked]<mailto:[email-masked]>>
Cc: OSPF WG List <[email-masked]<mailto:[email-masked]>>
Subject: OSPF Link Overload (aka, Graceful Link Shutdown) MAX-TE-METRIC

Hi Shraddha,

Given all work on TE, I was inclined to search for this constant in other documents. I think it would be useful to precede the definition with “This document defines MAX-TE-METRIC as 0xffffffe.” to avoid any confusion.

I was not aware some TE implementations did this. We definitely want it to be used as the least preferred path in this state.

I know that pre-RFC 2383 (not going to look up where it was actually changed) defined 0xffffff as unreachable and this was later deprecated.

I don’t feel strongly but would err on the conservative side if there are implementations that treat 0xffffffff as unusable.

Thanks,
Acee

Thanks,
Acee