IOS Routing Internals

Transcription

1 IOS Routing Internals Pete Lumbis CCIE R&S #28677, CCDE 2012::3 Routing Protocols Technical Leader RTP TAC

2 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

3 IOS Routing Internals Agenda Router Components Data and Control Planes Software Based Routers Hardware Based Routers Hybrid Routers Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

4 Router Components Data and Control Planes Control Plane Control Traffic Routing Updates (BGP, EIGRP, OSPF, etc.) SSH SNMP Data Plane Through traffic Brains Brawn 4

5 IOS Routing Internals Agenda Router Components Data and Control Planes Software Based Routers Hardware Based Routers Hybrid Routers Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

6 Router Components Software Based Routers Software Based Shared control and data plane General Purpose CPU (slow and smart) CPU responsible for all operations 2800/2900/3900/7200 Series Routers are software based 6

7 Router Components Software Based Routers RX Ring Tx Ring Network Interface I/O Memory Process Memory RAM CPU 7

8 IOS Routing Internals Agenda Router Components Data and Control Planes Software Based Routers Hardware Based Routers Hybrid Routers Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

9 Router Components Hardware Based Routers Hardware based Separated control and data plane CPU + ASIC (Application Specific Integrated Circuit) ASIC designed specifically to move packets (fast and dumb) CPU manages control plane CPU only moves packets the ASIC can t Data Plane packets sent to the CPU are punted 6500/7600, Nexus 7000 and ASR9000 are hardware based 9

10 Router Components Hardware Based Routers IO Memory Process Memory CPU RX Ring RAM Tx Ring TCAM Forwarding ASIC Network Interface 10

11 Router Components Hardware Based Routers Control Plane Data Plane RX Ring IO Memory Process Memory RAM CPU Tx Ring TCAM Forwarding ASIC Network Interface 11

12 IOS Routing Internals Agenda Router Components Data and Control Planes Software Based Routers Hardware Based Routers Hybrid Routers Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

13 Router Components Hybrid Routers Hardware assisted Separated control and data plane CPU + NP (Network Processor) NP is multi-core specialized processor NP is optimized to move packets CPU manages control plane CPU only moves packets the NP can t ASR1000 is a Hardware Assisted Router 13

14 Router Components Hybrid Routers Control Plane Data Plane RX Ring IO Memory Process Memory RAM CPU Tx Ring TCAM Forwarding ASIC Network Interface 14

15 Router Components Hybrid Routers Control Plane Data Plane RX Ring IO Memory Process Memory RAM CPU Tx Ring Dataplane Memory NP Network Interface 15

16 IOS Routing Internals Agenda Router Components Moving Packets Process Switching CEF Switching CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

17 Moving Packets Overview CEF Switching and Process Switching Fast Switching is deprecated as of 12.4(20)T Not covered today CEF Switching is the default Process Switching is the fallback Anything CEF can t handle 17

18 Process Switching CPU Interrupt L2 Hdr Packet e0/0 Rx Ring IO Memory e0/1 Tx Ring 18

19 Process Switching CPU Schedules IP Input Interrupt L2 Hdr Packet e0/0 Rx Ring IO Memory e0/1 Tx Ring 19

20 Process Switching CPU IP Input Runs Scheduler e0/0 Rx Ring IO Memory Packet e0/1 Tx Ring 20

21 Process Switching Routing Table Find Route Find Adjacency CPU L2 Hdr IP Input Scheduler ARP Table e0/0 Rx Ring IO Memory Packet e0/1 Tx Ring 21

22 Process Switching Routing Table CPU L2 Hdr IP Input Scheduler ARP Table e0/0 Rx Ring IO Memory Packet e0/1 Tx Ring 22

23 Process Switching Routing Table CPU IP Input Scheduler ARP Table e0/0 Rx Ring IO Memory L2 Hdr e0/1 Packet Tx Ring 23

24 Moving Packets Process Switching Process Switching is BAD Multiple lookups Inefficient data structures Process scheduling What can we do to improve? Better data structures Pre-compile forwarding information Router#show ip route Routing entry for /32 Known via "bgp 65530", distance 20, metric 0 * , from , 00:00:07 ago Router#show ip route Routing entry for /32 Known via "static", distance 1, metric 0 * Router#show ip route Routing entry for /24 Known via "connected", distance 0, metric 0 (connected, via interface) * directly connected, via Ethernet0/1 25

25 IOS Routing Internals Agenda Router Components Moving Packets Process Switching CEF Switching CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements

26 The FIB (Forwarding Information Base) Show IP CEF Routing Table Adjacency Table ARP Table Other L2 Protocols FIB (Software CEF) Hardware CEF (TCAM) Software Hardware 27

27 CEF Overview CEF Table = Route + Egress Interface + L2 Destination Single lookup (and faster too!) Router# show ip cef det /32 No process scheduling recursive via recursive via attached to Ethernet0/1 28

28 CEF Switching CPU Interrupt L2 Hdr Packet e0/0 Rx Ring IO Memory e0/1 Tx Ring 29

29 CEF Switching CPU IP Input Scheduler Interrupt Route + L2 Lookup L2 Hdr CEF Table L2 Hdr Packet e0/0 Rx Ring IO Memory e0/1 Tx Ring 30

30 CEF Switching CPU Interrupt Route + L2 Lookup L2 Hdr CEF Table e0/0 Rx Ring IO Memory Packet e0/1 Tx Ring 31

31 CEF Switching CPU Interrupt Route + L2 Lookup CEF Table e0/0 Rx Ring IO Memory L2 Hdr e0/1 Packet Tx Ring 32

32 CEF Switching - Summary Interrupt removes process scheduling Pre-compiled Interface + L2 information (cache) CEF table data structure improvement RIB is a hash CEF is a mtrie Single lookup for all necessary forwarding information 34

33 CEF Switching - Features Supported in CEF QoS ACL Zone Based Firewall NAT Netflow IPSec GRE PBR Many more! Process Switching Only ACL Logging Packets destined to the router No L2 Adjacency 35

34 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Processes and Interrupts Routing Memory Utilization Outbound Load Sharing Routing Convergence Improvements

35 CEF and CPU Utilization CPU does everything Total CPU vs. Interrupts SPF, BGP Routed Packets Total CPU Interrupts = Utilization Due to Processes CPU utilization for five seconds: 5%/2%; one minute: 3%; five minutes: 2% PID Runtime (ms) Invoked usecs 5Sec 1Min 5Min TTY Process % 1.00% 0% 0 IP Input % 1.00% 0% 0 BGP Router % 0% 0% 0 BGP Scanner... 37

36 CPU Utilization Examples 1. CPU Utilization due to moderate traffic rates CPU utilization for five seconds: 47%/46%; one minute: 40%; five minutes: 39% 38

37 CPU Utilization Examples 1. CPU Utilization due to moderate traffic rates CPU utilization for five seconds: 47%/46%; one minute: 40%; five minutes: 39% 2. High CPU due to OSPF Reconvergence CPU utilization for five seconds: 99%/3%; one minute: 53%; five minutes: 49% PID Runtime(ms) Invoked usecs 5Sec 1Min 5Min TTY Process % 41.18% 36.78% 0 OSPF-1 Router 39

38 CPU Utilization Examples 1. CPU Utilization due to moderate traffic rates CPU utilization for five seconds: 47%/46%; one minute: 40%; five minutes: 39% 2. High CPU due to OSPF Reconvergence CPU utilization for five seconds: 99%/3%; one minute: 53%; five minutes: 49% PID Runtime(ms) Invoked usecs 5Sec 1Min 5Min TTY Process % 41.18% 36.78% 0 OSPF-1 Router 3. High CPU due to multiple Virtual Exec Processes CPU utilization for five seconds: 99%/3%; one minute: 99%; five minutes: 99% PID Runtime(ms) Invoked usecs 5Sec 1Min 5Min TTY Process % 31.62% 31.57% 2 Virtual Exec % 31.62% 31.60% 3 Virtual Exec % 31.88% 31.31% 4 Virtual Exec 40

39 Process Priority Processes assigned priority Critical/High/Medium/Low Critical High Medium CPU Low 41

40 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler 3 Critical High 1 2 Medium CPU Low 42

41 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler 3 4 Critical High 1 2 Medium CPU Low 43

42 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Critical 4 High Medium CPU Low 44

43 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Critical 4 High 1 2 Medium CPU Low 45

44 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Critical High Medium CPU Low 46

45 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Critical High 1 2 Medium CPU Low 47

46 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Run to Completion Model 5 Critical High 1 CPU 2 Medium Low 48

47 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Run to Completion Model Processes choose to suspend 5 Critical High 1 CPU 2 Medium Low 49

48 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Run to Completion Model Processes choose to suspend 5 Critical High 1 2 Medium CPU Low 50

49 Process Priority Processes assigned priority Critical/High/Medium/Low Priority Scheduler Run to Completion Model Processes choose to suspend Interrupts break the rules 1 2 Critical High Medium Interrupt! CPU 5 Low 51

50 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Processes and Interrupts Routing Memory Utilization Outbound Load Sharing Routing Convergence Improvements

51 Routing Process Memory Routing Protocol, RIB, and CEF each take their own memory RIB built from Routing Protocols CEF built from RIB Proc Mem BGP RIB CEF {65534} { } via e0/ > e0/0, ace.face 53

52 Memory Impact of Multiple Prefixes ISP A ISP B ISP C 400k Prefixes 400k Prefixes 400k Prefixes 3 BGP Peers 400k Identical Routes 15.2(2)T 54

53 Memory Impact of Multiple Prefixes 50% 40% 30% 0 peers 0 BGP entries 0 CEF entries Memory Utilization 38% 41% 45% ISP A ISP B ISP C 20% 10% 0% 5% 0 Peers 1 Peer 2 Peers 3 Peers 3 BGP Peers 400k Identical Routes 15.2(2)T 55

54 Memory Impact of Multiple Prefixes 50% Memory Utilization 40% 30% 38% 41% 45% ISP A ISP B ISP C 20% 10% 0% 5% 1 peer 400k BGP entries 400k CEF entries 0 Peers 1 Peer 2 Peers 3 Peers 3 BGP Peers 400k Identical Routes 15.2(2)T 56

55 Memory Impact of Multiple Prefixes 50% Memory Utilization 40% 30% 38% 41% 45% ISP A ISP B ISP C 20% 10% 0% 5% 2 peers 800k BGP Entries 400k CEF entries 0 Peers 1 Peer 2 Peers 3 Peers 3 BGP Peers 400k Identical Routes 15.2(2)T 57

56 Memory Impact of Multiple Prefixes 50% Memory Utilization 40% 30% 38% 41% 45% ISP A ISP B ISP C 20% 10% 0% 5% 3 peers 1.2m BGP Entries 400k CEF entries 0 Peers 1 Peer 2 Peers 3 Peers 3 BGP Peers 400k Identical Routes 15.2(2)T 58

57 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing CEF Equal Cost Multipath (ECMP) Load Sharing with Performance Routing (PfR) Routing Convergence Improvements

58 Load Sharing vs. Load Balancing Load balancing implies intelligence Load sharing is simple Load balancing has fairness Load sharing has no measurements

59 Equal Cost Loadsharing OSPF Cost /24 OSPF Area 0 B OSPF Cost 20 61

60 Routing Table Equal Cost Routes RouterB#show ip route Routing entry for /24 Known via "ospf 1", distance 110, metric 20, type intra area Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: * , from , 1d02h ago, via Ethernet0/1 Route metric is 20, traffic share count is , from , 1d02h ago, via Ethernet0/0 Route metric is 20, traffic share count is 1 63

61 Routing Table Equal Cost Routes RouterB#show ip route Routing entry for /24 Known via "ospf 1", distance 110, metric 20, type intra area Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: * , from , 1d02h ago, via Ethernet0/1 Route metric is 20, traffic share count is , from , 1d02h ago, via Ethernet0/0 Route metric is 20, traffic share count is 1 64

62 Routing Table Equal Cost Routes RouterB#show ip route Routing entry for /24 Known via "ospf 1", distance 110, metric 20, type intra area Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: * , from , 1d02h ago, via Ethernet0/1 Route metric is 20, traffic share count is , from , 1d02h ago, via Ethernet0/0 Route metric is 20, traffic share count is 1 65

63 Unequal Cost Load Sharing EIGRP Cost /24 EIGRP 10 B EIGRP Cost

64 Routing Table Unequal Cost Routes RouterB#show ip route Routing entry for /24 Known via "eigrp 10", distance 90, metric , type internal Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: , from , 1d02h ago, via Ethernet0/1 Route metric is , traffic share count is * , from , 00:00:16 ago, via Ethernet0/0 Route metric is , traffic share count is 240 Unequal Metrics 68

65 Routing Table Unequal Cost Routes RouterB#show ip route Routing entry for /24 Known via "eigrp 10", distance 90, metric , type internal Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: , from , 1d02h ago, via Ethernet0/1 Route metric is , traffic share count is * , from , 00:00:16 ago, via Ethernet0/0 Route metric is , traffic share count is 240 Unequal Traffic Share Count 69

66 Routing Table Unequal Cost Routes RouterB#show ip route Routing entry for /24 Known via "eigrp 10", distance 90, metric , type internal Last update from on Ethernet0/0, 1d02h ago Routing Descriptor Blocks: , from , 1d02h ago, via Ethernet0/1 Route metric is , traffic share count is * , from , 00:00:16 ago, via Ethernet0/0 Route metric is , traffic share count is 240 Only Accomplished with EIGRP variance command 70

67 CEF Hashing CEF hash is deterministic Same input always provides the same output Packet 1 = src dst Packet 2 = src dst A 2 1 B C D E F G Without randomization every router makes the same decision Downstream routers never loadshare 72

68 CEF Hashing Algorithm Default hash is Universal Source IP + Destination IP + Universal Identifier Universal ID prevents polarization Other hashes can be used for fixing unequal load sharing RouterB#show cef state CEF Status: universal per-destination load sharing algorithm, id 0F33353C 73

69 CEF Loadsharing Options Per-Packet More even load sharing Jitter Out of Order packets (bad for lots of applications) Per-Destination (default) Can be less even load sharing Ordered delivery Hashing challenges 74

70 CEF Hashing RouterB#show ip CEF internal /24, epoch 0, RIB[I], refcount 5, per-destination sharing ifnums: Ethernet0/0(3): Ethernet0/1(4): path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/0, adj IP adj out Eth0/0, addr E35A0 path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/1, adj IP adj out Eth0/1, addr F75D9F8 flags: Per-session, for-rx-ipv4, 2buckets 2 hash buckets < 0 > IP adj out of Ethernet0/0, addr E35A0 < 1 > IP adj out of Ethernet0/1, addr F75D9F8 75

71 CEF Hashing RouterB#show ip CEF internal /24, epoch 0, RIB[I], refcount 5, per-destination sharing ifnums: Ethernet0/0(3): Ethernet0/1(4): path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/0, adj IP adj out Eth0/0, addr E35A0 path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/1, adj IP adj out Eth0/1, addr F75D9F8 flags: Per-session, for-rx-ipv4, 2buckets 2 hash buckets < 0 > IP adj out of Ethernet0/0, addr E35A0 < 1 > IP adj out of Ethernet0/1, addr F75D9F8 76

72 CEF Hashing RouterB#show ip CEF internal /24, epoch 0, RIB[I], refcount 5, per-destination sharing ifnums: Ethernet0/0(3): Ethernet0/1(4): path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/0, adj IP adj out Eth0/0, addr E35A0 path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/1, adj IP adj out Eth0/1, addr F75D9F8 flags: Per-session, for-rx-ipv4, 2buckets 2 hash buckets < 0 > IP adj out of Ethernet0/0, addr E35A0 < 1 > IP adj out of Ethernet0/1, addr F75D9F8 77

73 CEF Hashing RouterB#show ip CEF internal /24, epoch 0, RIB[I], refcount 5, per-destination sharing ifnums: Ethernet0/0(3): Ethernet0/1(4): path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/0, adj IP adj out Eth0/0, addr E35A0 path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/1, adj IP adj out Eth0/1, addr F75D9F8 flags: Per-session, for-rx-ipv4, 2buckets 2 hash buckets < 0 > IP adj out of Ethernet0/0, addr E35A0 < 1 > IP adj out of Ethernet0/1, addr F75D9F8 78

74 CEF Hashing RouterB#show ip CEF internal /24, epoch 0, RIB[I], refcount 5, per-destination sharing ifnums: Ethernet0/0(3): Ethernet0/1(4): path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/0, adj IP adj out Eth0/0, addr E35A0 path , path list A8, share 1/1, type attached nexthop, for IPv4 nexthop Eth0/1, adj IP adj out Eth0/1, addr F75D9F8 flags: Per-session, for-rx-ipv4, 2buckets 2 hash buckets < 0 > IP adj out of Ethernet0/0, addr E35A0 < 1 > IP adj out of Ethernet0/1, addr F75D9F8 79

75 CEF Hashing 2 hash buckets < 0 > IP adj out Ethernet0/0, addr E35A0 < 1 > IP adj out Ethernet0/1, addr F75D9F8 Source IP Destination IP Universal ID CEF Hash 0 1 or Eth0/0, Eth0/1,

76 CEF Hashing RouterB#show ip CEF exact-route > => IP adj out Ethernet0/1, addr RouterB#show ip CEF exact-route > => IP adj out Ethernet0/0, addr Source IP Destination IP Universal ID CEF Hash 0 1 or Eth0/0, Eth0/1,

77 Equal Cost Multipath - Summary CEF is built from the routing table Load sharing is part of routing decision Not 100% equal Based on Source IP + Destination IP + Universal ID Only one router How do I load share on more than one router? 82

78 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing CEF Equal Cost Multipath (ECMP) Load Sharing with Performance Routing (PfR) Routing Convergence Improvements

79 Loadsharing Across Routers CEF ECMP works per-router No dynamic way to get even sharing across routers 20% ISP1 WAN Site Enterprise 60% ISP2

80 PfR Operations Command and Control Infrastructure Border Routers (BRs) communicate load to Master Controller (MC) 20% MC BR Load Information ISP1 WAN Site BR 60% ISP2

81 PfR Operations Master Controller analyzes reports from Border Routers 20%? MC BR Load Information ISP1 WAN Site BR 60% ISP2

82 PfR Operations Master Controller analyzes reports from Border Routers MC detects policy violation 20%! MC BR Load Information ISP1 WAN Site BR 60% ISP2

83 PfR Operations Master Controller pushes routing updates 20%! MC BR Routing Updates ISP1 WAN Site BR 60% ISP2

84 PfR Operations Master Controller pushes routing updates Border Routers adjust routing impacting load 48% MC BR Routing Updates ISP1 WAN Site BR 40% ISP2

85 PfR Operations Border Routers continue reporting 48% MC BR Load Information ISP1 WAN Site BR 40% ISP2

86 PfR Operations Border Routers continue reporting Master Control continues analyzing 48%? MC BR Load Information ISP1 WAN Site BR 40% ISP2

87 PfR Summary PfR lifecycle Policy Enforcement BGP Local Preference Static Routes PBR PfR provides routing intelligence CEF and RIB are the same

88 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements Fast Convergence Overview OSPF LFA EIGRP Feasible Successor BGP PIC-Edge

89 Routing Convergence What s to Improve? Routing changes are bad Small changes can require (potentially) large recalculation Routing Protocols are slow Failure detection is fast Event propagation + calculation is the bottleneck Chain Reaction Protocol Change -> RIB Change -> CEF Change Protocol can already know what to do before failure 94

90 Failure Detection with BFD Bidirectional Forwarding Detection VERY fast (50ms hello/150ms dead) Lightweight 24 bytes BFD Hello vs. 56 byte OSPF Hello Handled in Interrupt Protocols are BFD clients Offloaded to hardware* *12k, 7600 with ES+ 95

91 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements Fast Convergence Overview OSPF LFA EIGRP Feasible Successor BGP PIC-Edge

92 OSPF Overview Link State Algorithm LSDB provides a view of the entire network Network changes exchanged via LSA (Link State Advertisement) Multiple events cause throttling (5000ms default) SPF algorithm determines best path Runs on receipt of LSA, delayed 5000ms (default) 97

93 OSPF Convergence Convergence = Failure Detection + Event Propagation + SPF + FIB Update Neighbor Down LSA generation RIB + CEF + Hardware Best case: ~160ms (SPF Tuning + BFD) Worst case: ~50 seconds (Dead Time + LSA throttle + SPF defaults) Failure Detection is easy (hardware) Control plane is difficult (software) 98

94 OSPF Loop Free Alternate B A C /24 A has a primary (A-C) and secondary (A-B-C) path to /24 Link State allows A to know entire topology A should know that B is an alternative path Loop Free Alternate (LFA) 99

95 OSPF Loop Free Alternate OSPF presents a primary and backup to CEF Backup calculated from secondary SPF run RouterA# show ip route Routing Descriptor Blocks: * , from , 00:01:57 ago, via Ethernet4/1/0 Route metric is 2, traffic share count is 1 Repair Path: , via Ethernet4/2/0 RouterA#show ip CEF /24 nexthop Ethernet4/1/0 repair: attached-nexthop Ethernet4/2/0 100

96 OSPF Loop Free Alternate Aims for <50ms reconvergence Triggers as soon as the failure is detected NO fast hellos Use BFD! Not enabled by default Added to 7600/ASR1000 in 15.1(3)S Added to NX-OS in 5.0(2) LFA milliseconds No LFA 101

97 OSPF Loop Free Alternate Fast failure detection is key! Single Box Not a replacement for SPF Tuning A C WAN B D 102

98 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements Fast Convergence Overview OSPF LFA EIGRP Feasible Successor BGP PIC-Edge

99 EIGRP Overview Distance Vector Protocol Doesn t see the entire network like OSPF Based on QUERY and ACK messages for convergence QUERY sent to determine best path for failed route ACK sent when alternative path found or no other paths DUAL algorithm determines best path Runs as soon as all outstanding QUERIES are received Query domain size can effect convergence time 104

100 EIGRP Feasible Successors EIGRP selects Successor and Feasible Successor Successor is the best route Feasible Successor is 2 nd best route Must be mathematically loop-free (meets feasibility condition) Feasible Successor acts as a backup route Kept in topology table (not routing table) Up to 6 Feasible Successors Built into the protocol, nothing to enable 105

101 EIGRP Feasible Successors Delay /24 EIGRP 10 B Delay 15 Metric based on bandwidth and delay 106

102 EIGRP Feasible Successors RouterB# show ip route Routing entry for /24 Known via "eigrp 10", distance 90, metric , type internal Routing Descriptor Blocks: * , from , 00:34:19 ago, via Eth0/1 Route metric is , traffic share count is /24 B 107

103 EIGRP Feasible Successors RouterB#show ip eigrp topology P /24, 1 successors, FD is via (285440/281600), Ethernet0/1 via (307200/281600), Ethernet0/0 Feasible Successor reported distance (281600) is less than Successor feasible distance (285440) Feasibility Condition met Instant convergence after Successor loss /24 B 108

104 EIGRP LFA Just like OSPF LFA Feasible Successors acts as Loop Free Alternate Installs Feasible Successors in hardware for instant failover EIGRP Fast Reroute available in S

105 EIGRP LFA RouterB#show ip route Known via "eigrp 10", distance 90, metric , type internal * , from , 00:00:17 ago, via Ethernet0/1 Route metric is , traffic share count is 1 Repair Path: , via Ethernet0/0 RouterB#show ip cef /24 nexthop Ethernet0/1 repair: attached-nexthop Ethernet0/0

106 IOS Routing Internals Agenda Router Components Moving Packets CEF, CPU and Memory Outbound Load Sharing Routing Convergence Improvements Fast Convergence Overview OSPF LFA EIGRP Feasible Successor BGP PIC-Edge

107 BGP Prefix Independent Convergence Today s RIB is flat / / / k routes -> 400k updates BGP often has same next hop We can do better! 400k prefixes A B 400k prefixes 112

108 BGP Prefix Independent Convergence Instead of flat FIB, Hierarchical / / /

109 BGP Prefix Independent Convergence Instead of flat FIB, Hierarchical / / /24 Next Hop Single change updates multiple entries Convergence time independent from prefix count 114

110 BGP PIC Core Primary: A-B-C Backup: A-D-C CE1 B C A CE /24 Prefixes / /24 D BGP Next Hop C IGP Next Hop B / / /

111 BGP PIC Core Primary: A-B-C Backup: A-D-C CE1 B C A CE /24 Prefixes / /24 D BGP Next Hop C IGP Next Hop B / / /

112 BGP PIC Core Primary: A-B-C Backup: A-D-C CE1 B C A CE /24 Prefixes / /24 D BGP Next Hop C IGP Next Hop B / / /

113 BGP PIC Core Primary: A-B-C Backup: A-D-C CE1 B C A CE2 Prefixes / / /24 D BGP Next Hop C IGP Next Hop B IGP Next Hop D / / /

114 BGP PIC Core Core LoC (ms) PIC no PIC Prefix BGP convergences starts after IGP convergence 119

115 BGP PIC Core PIC Core part of migration to hierarchical FIB Still requires IGP convergence OSPF LFA EIGRP FS and LFA PIC Edge Mainly for MPLS/VPN environments Fast convergence for edge node failures Beyond the scope of today s talk 120

116 Review Router Components Control vs. Data plane Software vs. Hardware vs. Hybrid based routers CPU and Memory Interrupt (CEF) vs. Process (Routing Protocol) Memory concerns for multiple routes Load Sharing CEF and PfR Routing Enhancements OSPF LFA/EIGRP Feasible Successors/BGP PIC 121

117 Further Reading 122

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