1. Hi High Availability Design Ram Dantu Slides are adopted from various sources from Cisco and Interwork Inc.,

2. Agenda Definitions Concepts / Calculations Examples Challenges

3. Availability as a percentage 1 year = 525960 minutes AvailabilityUnscheduled downtime per year 99%3 days 15 hours 36 minutes 99.9%8 hours 45 min. 99.99%52 min. 36 sec. 99.999%5 min. 15 sec. 99.9999%32 sec.

4. Getting downtime from availability 1 year = 525,960 minutes Uptime = availability * Time Annual Uptime = Availability * 525,960 Annual Downtime = 525,960 – Annual Uptime --------------------------------------------------------- Availability = 0.9999 Annual Uptime =.9999 * 525,960 Annual Uptime = 525,907.4 Annual Downtime = 525,960 – 525,907.4 = 52.596 ----------------------------------------------------------- Downtime = (1-Availability) * Time

5. Availability vs. Reliability Availability = users’ perception Reliability = individual component failures Reliability impacts maintenance costs but doesn’t necessarily have to impact availability

6. Defects Per Million AvailabilityDPM 99%10000 99.9%1000 99.99%100 99.999%10 99.9999%1

7. Calculating Availability Availability = MTBF MTBF + MTTR Example: 6500 Chassis MTBF = 369897 hours (about 42 years) MTTR = 4 hours Availability = 369897 / ( 369897 + 4 ) = 369897 / 369901 = 0.9999892 = 99.99892%

8. 6500 Availability ModuleAvailability Chassis99.99892% Power Supplies99.99873% Supervisor - including software99.99516% GBIC Line Card99.99577% GBIC99.99907% 10/100 Line Card99.99577%

9. Availability Formulas Serial availability Availability= Avail A × Avail B × Avail C = 99.999% × 99.999% × 99.999% = 99.997% ACB 99.999%

10. Availability Formulas Parallel availability Availability= 1 – ((1 – Avail A ) × (1 – Avail B )) = 1 – ((1 – 99.9%) × (1 – 99.9%)) = 99.9999% 99.9% B A

11. Availability Formulas Parallel-series availability 99.9% B A D C F E 99.9999%  = 99.9997%

12. Availability Formulas Series-parallel availability 99.7% = 99.9991% 99.9% B A D C F E = 1 – ((1 – 99.7%) × (1 – 99.7%))

13. Core Distribution Access

14. One Core / Distribution 6500 Chassis99.99892% Dual power99.99999% Supervisor + software99.99516% Dual GBIC Line Cards99.99999% Dual GBICs99.99999% Single switch availability99.99405%

15. Pair of Core / Distribution 6500’s Series-Parallel Availability 99.99405% series availability each Two switches in parallel 1 – ((1 – 99.99405%) × (1 – 99.99405%)) = 99.999999%

16. Access Layer 6500 Chassis99.99892% Dual power99.99999% Dual Supervisors99.99999% Dual GBIC Line Cards99.99999% Dual GBICs99.99999% 10/100 Line Card99.99577% Switch availability99.99888% Access port availability99.99465%

17. Challenges Improving availability at the access layer –“NIC Teaming” in servers –Reduce MTTR MTBF = 369897 hours Availability with MTTR of 4 hours = 99.99892% Availability with MTTR of 2 hours = 99.99945%

18. Challenges Long convergence times –Spanning tree Eliminate layer-2 links where possible Avoid layer-2 loops Use STP enhancements where appropriate –Routing protocols Use a link-state (or EIGRP) routing protocol Use routing convergence enhancements Minimize routing table sizes Limit convergence scope