Reverse Metric TLVdraft-amante-isis-reverse-metric-01

Authors:Shane Amante

Tony LiNaiming Shen

Mikael Abrahamsson

Proposed Status: Standards Track

Background

• Operational reqm’t to gracefully bi-directionally remove both p2p links and multi-access LAN’s from the ISIS topology, except as a link of last-resort

• DO NOT need or want to isolate the entire router with IS-IS overload-bit – potentially affecting Tbps of ‘innocent’ traffic

• Login to CLI of both (p2p) or all (LAN) devices and increase the existing IS-IS metric(s) to temporarily remove it from the topology

• Service Providers don’t, can’t and/or won’t use NMS to ‘automate’ this

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Current Link/LAN Isolation Procedures

• Current procedure to isolate link/LAN:– login to each router,– correctly identify specific link on both routers– Change existing, configured metric high to extremely high value– IS-IS domain should now consider Link/LAN as “link/LAN of last resort”

• To un-isolate link/LAN:– (Re-)login to each router,– Correctly identify specific link/LAN– Change metric back to originally configured value

R1 R2 R1 R2

R3 R4 R5 R6

P2P Link Multi-access LAN

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Challenges with link/LAN isolation

• Correctly identify the corresponding link on two or, more routers, each with hundreds of interfaces apiece @ 3AM in the morning …

• Need to temporarily change the existing, configured IS-IS metric on an interface (need to “remember” what it was to properly reset it afterward).

• Cannot bidirectionally isolate a single adjacency on a multi-access LAN.

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Solution: Reverse Metric TLV• Reverse Metric is wholly separate from, but added to,

existing configured default metric on local device and remote neighbor

• Login to a single node and temporarily assert an additive high metric in both:– Our own IS Reachbility or Ext. IS Reachability TLV’s– A Reverse Metric TLV in IIH’s xmit’ed toward your neighbor,

on p2p link, or toward DIS on multi-access LAN

• Router receiving Reverse Metric TLV adds to his/her own existing ‘default metric’ in Pseudonode LSP, IS Reachability or Ext. IS Reachability TLV

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Proposed Link/LAN Isolation Procedures

• Read draft or see slides online for specific proposed link/LAN procedures

R1 R2 R2

R3 R4 R5 R6

P2P Link Multi-access LAN

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IIH PDU’s withReverse Metric TLV

R2 New LSPR1 New LSPR1 New LSP

R1

Current Status

• LAN’s: This draft has similar concerns with persistent forwarding loops if nodes do not accumulate non-zero metric in Pseudonode LSP, as already discussed for draft-shen-isis-oper-enhance

• Addressed large # of comments on mailing list in -00 -01 version

• Questions? Comments?• Interest in advancing this draft, in the future?

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Backup Material(Detailed Procedures)

Proposed p2p Link Isolation Procedures

R1 Procedures:• login to one router, (R1)• correctly identify specific link• Apply new, additive IS-IS metric

with extremely high value to link – leave existing, configured metric “as is”.

• In no particular order:– Update own IS Reachability, Ext. IS

Reachability TLV– Flood new LSP’s– Recalculate SPF Tree– Add Reverse Metric TLV to IIH PDU’s

toward neighbor(s) – R1 R2

R2 Procedures:• When R2 receives Reverse Metric

TLV• In no particular order:

– Add “metric value” in Reverse Metric TLV to own IS Reachability or Ext. IS Reachability TLV’s of link on which Reverse Metric TLV is recv’d

– Flood new LSP’s– Recalculate SPF Tree

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Proposed p2p Link Un-Isolation Procedures

R1 Procedures:• login to one router, (R1)• correctly identify specific link• Remove additive IS-IS metric with

extremely high value to link – leave existing, configured metric “as is”.

• In no particular order:– Update own IS Reachability, Ext. IS

Reachability TLV– Flood new LSP’s– Recalculate SPF Tree– Stop sending Reverse Metric TLV in

IIH PDU’s toward neighbor(s) – R1 R2

R2 Procedures:• When R2 stops receiving Reverse

Metric TLV• In no particular order:

– Remove additive “metric value” (from Reverse Metric TLV) in own IS Reachability or Ext. IS Reachability TLV’s of link on which Reverse Metric TLV was formerly recv’d

– Flood new LSP’s– Recalculate SPF Tree

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Proposed multi-access LAN Isolation ProceduresR4 (Non-DIS) Procedures:• login to one router, (R4)• correctly identify specific link• Apply new, additive IS-IS metric

with extremely high value to link – leave existing, configured metric “as is”.

• On R4 (non-DIS), in no particular order:

– Update own IS Reachability, Ext. IS Reachability TLV

– Flood new LSP’s– Recalculate SPF Tree– Add Reverse Metric TLV to IIH PDU’s

toward DIS – R4 R1

R1 (DIS) Procedures:• When R1 receives Reverse Metric

TLV:– Update Pseudonode LSP with non-

zero metric – add “metric value” in Reverse Metric TLV – to either R4 (W=0) or all nodes on LAN (W=1)

– Flood new Pseudonode LSP– Recalculate SPF Tree

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Other non-DIS nodes on same LAN,(R3, R5, R6), ignore Reverse Metric TLVfrom R4; however, each will receiveUpdated Psuedonode LSP from DISAnd recalculate their SPF for otherNode(s) attached to the LAN.

Proposed multi-access LAN Un-Isolation Procedures

R4 (Non-DIS) Procedures:• login to one router, (R4)• correctly identify specific link• Remove additive IS-IS metric with

extremely high value to link – leave existing, configured metric “as is”.

• On R4 (non-DIS), in no particular order:

– Update own IS Reachability, Ext. IS Reachability TLV

– Flood new LSP’s– Recalculate SPF Tree– Stop sending Reverse Metric TLV to

IIH PDU’s toward DIS – R4 R1

R1 (DIS) Procedures:• When R1 stops receiving Reverse

Metric TLV:– Update Pseudonode LSP back to

original, zero metric based on previous assertion in the Reverse Metric TLV from R4, i.e.: just R4 (W=1) or Whole LAN (W=0)

– Flood new Pseudonode LSP– Recalculate SPF Tree

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Other non-DIS nodes on same LAN,(R3, R5, R6), receive new Psuedonode LSPfrom DIS and recalculate their SPF for othernode(s) attached to the LAN.