Download presentation

Presentation is loading. Please wait.

Published byHunter Barry Modified over 3 years ago

1
Nov 2009IEEE 802.1aq Atlanta IEEE 802.1aq Shortest Path Bridging Equal Cost Tree (ECT) Framework Proposal Peter Ashwood-Smith incorporating graphics by: Guoli Yin incorporating MCID input from: Nigel Bragg ECT from : Mick Seaman (per –d2-1) 1

2
Nov 2009IEEE 802.1aq Atlanta Presentation Structure There are strict requirements on ECT algorithms compatible with SPB : –we summarise these Nonetheless, a number of different algorithms have been identified and successfully prototyped : –we give a couple of examples So what is the best way to preserve rigour and allow future algorithm innovation ? Define an extensible Framework (compatible with previous work). and populate it initially with currently known and validated algorithms 2

3
Nov 2009IEEE 802.1aq Atlanta Algorithm requirements review: Shortest paths computed by SPB must be symmetric and downstream congruent. Symmetry required for: Learning in the case of SPPV Ingress checking (SA lookup miss => discard) for SPPM Downstream congruence required for: Hop by hop destination-based (DA/VID) forwarding, every hop agrees on same rest of path, so state scales O(N) vs. O(N 2 ) Equal cost shortest paths computed by SPB must be resolved by a technique which is independent both of the direction of computation and the location in the topology of the computing node. 3

4
Nov 2009IEEE 802.1aq Atlanta Tie-Breaking – base algorithm When only one shortest path there is no issue. When two equal min sum of link metric paths exist must deterministically pick 1. Basic tie breaker is called LowPathID : a lexicographically ordered list of the BridgeIds forming the Path LowPathId will pick path with the minimum BridgeId between fork/join points. LowPathId is trivial to implement in Dijkstra, just backtrack when join occurs: Track min BridgeId on each path until they converge (fork point). LowPathId is the path with the min of the two mins between fork/join. BridgeId = BridgePriority concatenated with SysIID Winner can be tuned by adjusting BridgePriority Min= Min=2 joinfork 4

5
Nov 2009IEEE 802.1aq Atlanta HOW DOES IT WORK IN PRACTICE? Low PathID As applied to a 7 member E-LAN ISID 100 all members support both transmit/receive. SPF tree shown from each member : using Low PathID algorithm. Symmetry highlighted Between 35 and 40. N 5 Animated GIF, run interactive to view.

6
Nov 2009IEEE 802.1aq Atlanta Tie-Breaking – 15 additional algorithms allow ECT There are 15 additional algorithms defined, allows ECT diversity. Each starts by running a 1:1 permutation on the BridgeIDs with XOR against known (network-global) masks. The LowPathID algorithm #1 is run after XOR with mask 0x0 (no change). For example, algorithm #2 will invert all the bytes in the BridgeID. We have been calling this highPathId so uses all 1s as its mask. Each of the other 14 algorithms uses a different bit mask to XOR the BridgeID into a new unique permutation. We implement all 16 by XOR-ing with the mask and finding min of min. The masks are as follows (in hex), each nibble in 8 byte mask uses same value. 00 ff cc bb aa 99 dd ee 6

7
Nov 2009IEEE 802.1aq Atlanta #S #D 0 | FF | 22 1 | FE | 23 0 | FF | 22 2 | FD | 20 0 | FF | 22 3 | FC | 21 #1#2#3 XOR-MASKs RESULT N = min {BridgeID XOR MASK[i]} #N = Bridge ID Low Path ID (alg=1) High Path ID (alg = 2) Alg=9 EXAMPLE ECT diversity for Algorithms 1,2 and 9 KEY #1 xor 0 = 1 #1 xor FF = FE #1 xor 22 = 23 #2 xor 0 = 2 #2 xor FF = FD #2 xor 22 = 20 #3 xor 0 = 3 #3 xor FF = FC #3 xor 22 = 21 BridgeID INPUT 7

8
Nov 2009IEEE 802.1aq Atlanta HOW DOES IT WORK IN PRACTICE? 8 X ECT 66 nodes Metro style 8 x ECT 36 node DS-style/fat HUGE improvement over Low/high PathID (x 2 ECT). But routes get missed because: If Diameter = D and avg adjacency = A there are: O((A-1 )D) paths. What other approaches can we take to maximize diversity? Animated GIF, run interactive to view. 8

9
Nov 2009IEEE 802.1aq Atlanta There seem to be numerous different classes of ECT algorithm with different properties. 1.Minimum/Max of some nodal identifier over paths. 1:1 Permutations of that identifier to spread min around. Operator can explicitly set identifiers to tweak spreading. 2.Minimum/Max of some link identifier over paths. 1:1 Permutations of that link identifier to spread min around. Operator can override link id to tweak spreading. 3.Minimum/Max of a sum of a secondary metric. Hash produces the secondary metric. User can override the secondary metric to tweak spreading. 4.Algorithms which consider previous ECT algorithms path usage to increase diversity. (Requires serial run instead of parallel). 9

10
Nov 2009IEEE 802.1aq Atlanta Since there seems to be a rich area of research to look into new ECT algorithms and with proper ECT diversity a form of traffic engineering emerges. So we propose: 1.Fix the 16 ECT algorithms as defined in –d2-1 and advance the spec…but 2.Include a framework that allows new ECT algorithms to be implemented. 3.Framework to include hello/LSA policies & TLVs for safe migration. 4.Framework includes concept of Opaque ECT-DATA on a node or link basis for future ECT algorithms. 5.Vendors/Researchers and future standards work can build into this framework without changes to IETF ISIS work or even IEEE 802.1aq. Vendors could sell proprietary ECT behaviors or publish informational. Other standards bodies can add custom behaviors, Data Center etc. 10

11
Nov 2009IEEE 802.1aq Atlanta The proposal – full text submitted to Don Fedyk ECT-ALGORITHM ::= OUI:24 || INDEX:8 OUI = C2, INDEX 0-16 defined by 802.1aq. 0=STP, 1=LowPathID etc. ISID ECT-ALGORITHM So we expand from 8 bit Algorithm to 32 bits in SPB Instance sub TLV. HELLO { } * Hello protocol carries algorithm identifier and VID used and indication of its current usage state for clean migration. LSP { }* Announces support for given algorithm and the VID to use. SPBM ECT-VID and DATA-VID are the same and are just the B-VID. Otherwise SPBV then ECT-VID is Base-VID and DATA-VID is the SPVID. LSP OPAQUE-NODE-ECT-TLV || ECT-ALGORITHM … ECT-DATA LSP OPAQUE-LINK-ECT-TLV || ECT-ALGORITHM … ECT-DATA Allows future expansion. 11

12
Nov 2009IEEE 802.1aq Atlanta ECT MIGRATION USE-FLAGs should be advertised when ISIDs reference an ECT-ALGORITHM. Hellos should set USE-FLAG if they are locally referencing or remotely seeing references to the ECT-ALGORITHM. Adjacency permitted if {, } * match. If mismatch for a given ECT-ALGORITHM the adjacency is allowed only if USE-FLAG not set on at least one end. this allows a new ECT-ALGORITHM to be introduced gradually whilst the network continues running the current production algorithm Must not locally use an ECT-ALGORITHM unless all adjacencies agree on ECT-VID. This should permit a new ECT-ALGORITHM to be turned on, advertised and then migrated to. It also permits movement away from an ECT-ALGORITHM and then the deprecation of that ECT-ALGORITHM network wide once no longer in use. 12

13
Nov 2009IEEE 802.1aq Atlanta MCID – migration issues (SPB only) 1.It may not be possible to accurately populate the VID space a priori. 2.and since we do not want to take down an adjacency just because we are adding a new un anticipated VID 3.We propose to allow an AUX-MCID to be advertised. 4.An adjacency is not rejected if the primary MCIDs dont match as long as there is a match of the AUX-MCID with the primary MCID. i.e. either the primary OR the auxiliary MCID of one bridge must match the primary MCID of the other to keep the adjacency up. 5.This allows configuration of one end of a link followed by out of sync configuration of the other end without loss of adjacency. 6.Responsibility for ensuring that primary and auxiliary MCIDs represent compatible super/sub-sets of VIDs lies with the network administrator but in-service upgrade of this sort is not for the amateur anyway 13

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google