TRILL ECN Support drafteastlaketrillecnsupport00 txt Donald E Eastlake

TRILL ECN Support draft-eastlake-trill-ecn-support-00. txt Donald E. Eastlake, 3 rd d 3 e 3 e 3@gmail. com Bob Briscoe ietf@bobbriscoe. net

ECN Background Mark, not drop, packet at congestion onset used extensively in data centres L 3 switches mark the IP header Enduring incremental deployment problem if legacy receiver or sender would not understand marking usually for low queue delay with Data Centre TCP (DCTCP) congested buffer MUST drop not mark otherwise legacy hosts would black-hole congestion signals Solution for e 2 e transports over IP (eg. TCP, RTP) e 2 e ECN capability negotiation at flow set-up IP-ECN codepoints for “ECN-capable transport” (ECT) then congested buffers: mark ECT packets or drop Not-ECT packets IP-ECN codepoint value meaning Not-ECT 00 Not ECN-capable transport ECT(0) 10 ECT(1) 01 ECN-Capable Transport CE 11 Congestion Experienced ('marked') April 2016 Explicit Congestion Notification (ECN) in IP [RFC 3168] TRILL ECN Support 1

Adding ECN to TRILL: the problem if legacy egress does not understand ECN will not propagate upward to forwarded IP inner header would black-hole congestion signals Three potential types of solution: 1. require TRILL RBridges to act as “L 3 switches” and mark IP-ECN field 2. require ingress-egress ECN capability negotiation (via routing) 3. use a critical ingress-to-egress flag April 2016 Similar incremental deployment problem TRILL ECN Support rest of talk #1: set aside as unreasonable #2: described first and in [draft-eastlake-trill-ecn-support 00] #3: described second but not in draft yet (developed after draft deadline) 2

Approach #2: Requires ingress -egress ECN negotiation ECN value codepoint meaning Not-ECT 00 Not ECN-capable transport ECT(0) 10 ECT(1) 01 ECN-Capable Transport CE 11 Congestion Experienced TRILL ECN Support 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Crit. | CHb. H | NCHb. H |CRSV | NCRSV | CIt. E | NCIt. E | |. . . . . | |C|C|C| |C|N| | | Ext | | |Ext| | |R|R|R| |R|C| | | Hop | | |Clr| | |H|I|R| |C|C| | | Cnt | | |b|t|s| |A|A| | | | |H|E|v| |F|F| | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ April 2016 Non-Critical Hopby-Hop Bits 3

Approach #2: ECN negotiated between ingress and egress “Tunnel” Ingress RBridge Transit TRILL Header ECT marking if (a) traffic was marked as ECT & (b) ingress and egress support ECN Possible ECN marking Transit Congestion experience in TRILL path combined with tunneled ECN indication [RFC 6040] Egress announced it would support this TRILL ECN Support End Station April 2016 Possible ECN marking Egress RBridge End Station 4

Approach #3: Defer mark / drop decision to egress ECN codepoint value meaning Not-ECT 00 Not ECN-capable transport ECT(0) 10 ECN-Capable Transport ECT(1) 01 CS 11 Congestion Signlled (Reserved for future use) TRILL ECN Support 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Crit. | CHb. H | NCHb. H |CRSV | NCRSV | CIt. E | NCIt. E | |. . . . . | |C|C|C| |C|N| | | Ext | |Ext| | |R|R|R| |R|C| | | Hop | |Clr| | |H|I|R| |C|C| | | Cnt | | | |b|t|s| |A|A| | |H|E|v| |F|F| | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ April 2016 Critical Ingress-to -Egress Bits Non-Critical Hopby-Hop Bits Congestion Experienced CE flag 5

Approach #3: Defer mark / drop decision to egress “Tunnel” Ingress RBridge Copy traffic ECN field to Non-Critical Hop-by-Hop TRILL ECN field (not necessary for ‘Classic’ [RFC 3168] ECN, but needed for variants. No ingress or transit dependence on Egress capabilities Congested transit RBridge that supports ECN marks using CE flag (Critical Ingress-to-Egress) No transit checking for ECT Transit Possible ECN marking TRILL ECN Support End Station April 2016 Possible ECN marking Transit Egress RBridge Two cases: 1. Egress supports ECN decap, correctly combines outer TRILL ECN with inner IP ECN [RFC 6040] 2. Egress doesn't understand ECN, drops any frame with a CIt. E bit set (Default behavior, which is desired) End Station 6

Recap: ECN tunneling rules at egress [RFC 6040] Not-ECT ECT(0) ECT(1) CE Not-ECT drop ECT(0) ECT(1) CE ECT(1) CE CE CE Outgoing header • TRILL egress same as [RFC 6040] but 3 ECN bits in proposal #3 so map 3 bits to the 4 codepoints as shown in table: NCHb. H TRILL ECN CIt. E TRILL ECN Incoming Outer 00 0 Not-ECT 10 0 ECT(0) 01 0 ECT(1) 11 0 CE 00 1 CE 10 1 CE 01 1 CE 11 1 CE CE April 2016 incoming outer TRILL ECN Support incoming inner 7

• Call for WG Adoption TRILL ECN Support • Ask for comments on the mailing list April 2016 Next Step 8

SUPPLEMENTAL SLIDES 9 TRILL ECN Support April 2016

outgoing outer Normal mode (default) Compatibility mode Not-ECT ECT(0) Not-ECT ECT(1) Not-ECT CE CE Not-ECT TRILL ECN Support incoming header (also = outgoing inner) April 2016 Recap: ECN tunneling rules at ingress [RFC 6040] 10

Adding support to TRILL for Low Latency Low Loss Scalable throughput (L 4 S) DCTCP sender Reno sender draft-briscoe-aqm-duaq-coupled, draft-briscoe-tsvwg-ecn-l 4 s-id ECT(1) & CE(1) (L 4 S) IP-ECN Classifier Classic Not-ECT & ECT(0) ECN marker 1 Coupling Time-shifted FIFO scheduler Drop April 2016 for background on L 4 S see: TRILL ECN Support On TRILL RBridge, use solution #3 “defer mark/drop decision” plus: classify on NCHb. H TRILL ECN field, as shown above Classic queue: if (p' > max(random(), random() ) { mark(frame, CE(0) } L 4 S queue: if (p' > random() ) { if (p' > random() ) mark(frame, CE(0) ) else mark(frame, CE(1) ) } then deferring mark/drop decision to egress gives desired outcome 11

End Donald E. Eastlake, 3 rd d 3 e 3 e 3@gmail. com Bob Briscoe ietf@bobbriscoe. net