**4.4 Changes of BGP routing tables**

Table 1 shows the registered routing policy table of the Asia Pacific R&E networks. It can be observed that ASTI (PH) lost connectivity to the R&E networks, that CSTNET (CN) lost eastbound routes, and that APAN-JP (JP) lost connectivity to TEIN2.

CERNET (CN) had a direct connection to TW, but after the earthquake its connection was expected to be changed to the path through US, as shown in Fig. 10. But, the routing policy arrangement was different between JP and KR. The forward path between CN and TW chose the route through JP but the return path chose the route through US as shown in Fig. 11.

In addition, routing from JP to the "west" Asian networks (Fig. 5) was connected through US. The direct link between CSTNET (CN) and US was also damaged.

Both CERNET and APAN Tokyo XP expect that the detour for JP-CN traffic should be through US, not through KR. Figure 10 shows the expected BGP route and the actual route between APAN-TW and CN. Since only APAN Tokyo XP implemented the strict routing policy, the CN traffic chose the shortest AS path. However, the traffic from JP to CN chose a routing policy that does not choose the route through KR.

Experience with Restoration of Asia Pacific Network Failures from Taiwan Earthquake 371

To investigate the BGP route changes in detail, we used an AS-topology visualization tool called "ABEL2" (Sakiyama et al., 2006) that utilizes BGP routing tables that are stored every

Fig. 12. After the earthquake at 19:30, Dec. 27 (UTC+9) 2006, the route from APAN-KR to GÉANT was diverted to a long AS path of (APAN-KR, APAN-JP, TransPAC, Abilene,

Fig. 13. Reconfigured AS path from APAN-KR to GÉANT (APAN-KR, CERNET, TEIN2-N,

Figures 12, 13, and 14 show the changes between APAN-KR (AS9270) and GÉANT (AS20965) by the number of IP prefixes. It can be observed in Fig. 12, that just after the earthquake, at 19:30 on December 27th (UTC+9), 2006, the route from APAN-KR to GÉANT was diverted to the long AS path APAN-KR - APAN-JP - TransPAC (US) -

**4.5 AS-level topology changes** 

10 minutes.

GÉANT)

GÉANT) at 20:30, Dec. 27 (UTC+9) 2006


Table 1. The monitored routing table for each R&E network on Dec.27 2006 (Kurokawa, 2006)

Fig. 10. BGP route changes of APAN before earthquake (Dec. 2006)

Fig. 11. BGP route changes of APAN after earthquake (Dec. 2006)
