Download presentation

Presentation is loading. Please wait.

Published byJacob Godley Modified over 2 years ago

1
Ethernet Data Center Routing Challenges and 802.1aq/SPB new work PETER ASHWOOD-SMITH peterashwoodsmith@huawei.com

2
802.1aq’s 16 ECT can give perfect spread going 2 hops 16 uplinks. However: A) Need to tweak 2 nd layer switch priorities to guarantee all 16 are used. B) Need at least 16 subnets (C/S-Vlan’s) to assign one per 802.1aq B-VID. A) Tweak Bridge Priorities Here S 1 … S 16 B)

3
Can we eliminate ‘tweaking*’ David Allan et al. have a presentation on this so I won’t spend much time on it. In general a network with N equal cost paths from ‘some source’ to ‘some destination’ requires #ECT about 25-40% greater than N (to statistically capture them all). Therefore when #ECT == N some ‘tweaking’ is usually required (for DC its trivial to do however). Dave et al. suggest non-independence between ECT algorithms as way to address this (maximize diversity) … *Tweaking = adjusting Bridge Priorities up/down from defaults.

4
A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 48 switch non blocking 2 layer L2 fabric 16 at “upper” layer A 1..A 16 32 at “lower” layer B 1.. B 32 16 uplinks per B n, & 160 UNI links per B n 32 downlinks per A n “Example” 802.1aq switching cluster – assume 100GE NNI links/groups (16 x 100GE per B n )x32 = 512x100GE = 51.2T 160 x 10GE server links (UNI) per B n (32 x 160)/2 = 2560 servers @ 2x10GE per uFIB = 16 x 48 B-mac = 768 entries mFIB = 16 subnet x 48 src = 768 entries 16 x 32 x 100GE = 51.2T using 48 x 2T switches S 3,1 S 3,160 S 32,1 S 32,160 S 1,1 S 1,160 5120 x 10GE 16 x 100GE 160 x 10GE 32 x 100GE 1536 FIB/node Good numbers “16” & “2” levels.

5
For a given ECT-ALG k, A j is a member of every SPF-TREE(B *,ECT-ALG k ) Properly tuned no two ECT-ALGorithms will use the same A j as a fork point. S 1 … S 16 ECT-ALG #12 Source Node (1)

6
A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 Subnet N i maps to I-SID j and then to a unique A (j mod 16 ) So load spreading allows each A i to transit a complete subnet. Problem#1 - Unable to further spread such that A i and A j (i != j) each handle subset of flows in I-SID j I-SID j I-SID i

7
A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 This is an issue under failure of A j Recovery will move entire subnet traffic to another A i node. A preferable solution is to spread affected load over remaining A * I-SID j I-SID i

8
A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 Possible solution – head end hashing (unicast only) Allow unicast I-SID i and I-SID j traffic to be hashed based on smaller flows to different B-VIDs (ECT-ALGorithms) This breaks the symmetry and congruence rules but allows edge balancing at smaller granularity. No changes to multicast. Requires learning, independent of B-VID I-SID j I-SID i Unicast Mcast

9
A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 A 15 A 16 B 32 B 31 B 30 B 29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 Interconnection of fabrics creates more than 16 paths (exponential ) C1C1 C2C2 Number of paths can grow exponentially with increasing levels. Constant number of paths always << number of paths in many networks. Growing 802.1aq ECT to say 32 or even 100 ECMP causes larger unicast FIBs. O(16) O(16x2) O(16x2x16)

10
A 15 A 16 B32B32 B31B31 B30B30 B29B29 A1A1 A2A2 B4B4 B3B3 B2B2 B1B1 Horizontal Growth – not too bad but need more ECT-ALGORITHMS. Horizontal growth by 1 just increases number of ECT by 1 Not too big a problem but we would need to define new ECT (via Opaque). B34B34 B33B33 A 17

11
General Issue O(degree) O(diameter) #paths ~= O( diameter degree ) So head end ECT in worst case requires O(exp(# B-VIDs)) S D Choose path from N x B-VID

12
A feasible solution … Re-assign traffic to path at each hop Tandem “ECMP” just like IP. Need to keep O(degree) number of next hops Only need one B-VID.. removes O(diameter) from state cost Flip side is you have no control – just hope for fine scale statistical distribution Choose path from N x nxt hop S D Choose path from N x nxt hop Single B-VID

13
What about loops in this mode? 802.1aq Ingress Check is very strong in the case of a single next hop and hence a single possible ingress for an SA. 802.1aq Ingress Check is weakened in the case of a multiple next hop and hence Multiple possible ingress for an SA. However 802.1aq Agreement Protocol functions correctly in the context of multiple possible Next Hops for the same B-VID (refer to Mick’s proof). But …

14
Agreement Protocol Concerns Is it too complex? it is clearly non trivial, we need implementation/ emulation experience. Is it overly Draconian. For example the bounds on movement are what is required for a mathematical proof by induction.. However there are probably many cases where further movement would not loop. What is the degree of ‘overkill’ ? Is it marketable? – this is unfortunately a legitimate concern!!! 802.1aq can be deployed without AP until we introduce hash based forwarding at which point we either require a symmetric AP and/or an on-data-path loop detection/drop mechanism. Believe that an on-data-path loop detection mechanism is required for hash based ECMP until we have more experience with AP. Recommend we standardize a TTL TAG either stand-alone or as a new form of I-TAG.

15
View of New Work Requirements R1) New ECT-ALGorithms with improved spreading properties. R2) Allow optional head end hash assignment of 802.1aq SPBM UNI known unicast traffic to one of multiple next hop interfaces/B-VIDs. Very similar to Link Ag. Minimally HASH (seed, C.SA, C.DA, C-VID, [ IP.SA, IP.DA, IP.PROTO] ) R3) Allow optional tandem hash assignment of 802.1aq SPBM B-VID NNI unicast traffic to one of multiple next hop interfaces. Essentially a new SPBM ECT-ALG with its own B-VID. (i.e. new ECT-ALGorithms, all usable at same time) Minimally HASH (seed, B-VID, C.SA, C.DA, C-VID, [ IP.SA, IP.DA, IP.PROTO ]) R4) minor OA&M changes in support of R2 and R3, because symmetry/congruence broken. R5) More experience with AP, emulations, simulations etc. + addition of TTL to new I-TAG or a TTL-TAG.

Similar presentations

OK

1 EE384Y: Packet Switch Architectures Part II Load-balanced Switch (Borrowed from Isaac Keslassys Defense Talk) Nick McKeown Professor of Electrical Engineering.

1 EE384Y: Packet Switch Architectures Part II Load-balanced Switch (Borrowed from Isaac Keslassys Defense Talk) Nick McKeown Professor of Electrical Engineering.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on sales order processing Download ppt on indus valley civilization timeline Ppt on conference call etiquette you need to know Ppt on maths for class 3 Ppt on tcp/ip protocol suite Ppt on paper tablet pc Ppt on electricity in india Ppt on service oriented architecture soa Ppt on congruent triangles for class 7 Ppt on airport management system