IS-IS Operational Enhancements for Network Maintenance Events draft-shen-isis-oper-enhance -00

1. IS-IS Operational Enhancements for Network Maintenance Eventsdraft-shen-isis-oper-enhance-00 Authors: Shane Amante Tony Li NaimingShen MikaelAbrahamsson Proposed Status: Informational Track

2. Background • Problem #1: Operational reqm’t to gracefully shutdown the IS-IS protocol on a LAN interface1 • Problem #2: Bi-directionally remove one or all nodes attached to a 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 • DO NOT want to login to CLI of all devices on LAN 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’ the changing of IS-IS metrics 1And, also, p2p interfaces as well; however, p2p interfaces are not in-scope for this draft. draft-amante-isis-reverse-metric-00

3. Fast Exit Notification: Problem • On a link/LAN, when you disable IS-IS protocol, the neighbor will wait up to “Hold Time” seconds (could be several seconds) before: • Removing the adjacency • Updating its IS Reachability, Ext. IS Reachability TLV’s • Flooding new LSP’s • Recalculating new SPF • Meanwhile, packets sent by other devices through that neighbor may be blackholed draft-amante-isis-reverse-metric-00

4. Fast Exit Notification: Solution • Exploit 3-way handshake on p2p & LAN’s • When IS-IS protocol is disabled/shutdown on a node’s interface, it sends out a final IS-IS Hello (IIH) PDU that DOES NOT contain neighbor’s System ID • Node may send out up to 3 “FEN” IIH PDU’s to ensure neighbor receives it – FEN considered “Best Effort”, i.e.: not reliable/guaranteed. draft-amante-isis-reverse-metric-00

5. Current LAN Isolation Procedures Multi-access LAN • Current procedure to isolate LAN: • login to each router, • correctly identify specific link on ALL routers • Change existing, configured metric high to extremely high value • IS-IS domain should now consider LAN as “LAN of last resort” • To un-isolate LAN: • (Re-)login to each router, • Correctly identify specific LAN interfaces • Change metric back to originally configured value R1 R2 R3 R4 R5 R6 draft-amante-isis-reverse-metric-00

6. Challenges with LAN isolation • Correctly identify the corresponding link on ALL routers attached to LAN, each with hundreds of interfaces apiece @ 3AM in the morning … • Need to temporarily change the existing, configured IS-IS metric on all interfaces on LAN & need to “remember” what it was to properly reset it afterward. • Cannot bidirectionally isolate a single adjacency on a multi-access LAN. draft-amante-isis-reverse-metric-00

7. Proposed Link/LAN Isolation Procedures Multi-access LAN R1 New LSP • Read draft or wait for next slide for specific procedures R1 R2 R3 R4 R5 R6 draft-amante-isis-reverse-metric-00

8. Solution: DIS updates non-zero metric in Pseudonode LSP • Login to DIS and temporarily assert a non-zero “default-metric” in the Pseudonode (PN) LSP: • DIS can change metric for several nodes in PN LSP; or, • DIS can change metric for all nodes in PN LSP • After modifying Pseudonode LSP, DIS floods new PN LSP to all nodes in IS-IS domain • All nodes receive new PN LSP, recalculate SPF tree by adding non-zero default-metric in PN LSP1 and divert traffic away from LAN. 1See next slides. draft-amante-isis-reverse-metric-00

9. How do implementations handle non-zero metric in Pseudonode LSP? • Concern that forwarding loops could result if nodes ignore (don’t accumulate) non-zero metric in PN LSP • Two scenarios to be concerned about: • Nodes directly attached to same LAN as PN LSP • Nodes >= 1 hops away from LAN draft-amante-isis-reverse-metric-00

10. Implementation Survey Results Received responses from 4 separate vendors maintaining 6 implementations. Survey results, based on Lab testing: • Implementation DOES accumulate non-zero metric in PN LSP when directly attached to same LAN: • YES: 4 • NO: 2A • Implementation DOES accumulate non-zero metric in PN LSP when >= 1 hops away from same LAN: • YES: 6 • NO: 0 1Both vendors have already expressed willingness to update their implementations to change from “NO” to “YES”, should this concept move forward. draft-amante-isis-reverse-metric-00

11. Next Steps • Questions? Comments? • Interest in advancing this draft, in the future? draft-amante-isis-reverse-metric-00