**4.1 Fiber breaks**

On December 26th, 2006 (UTC+9) there were two huge earthquakes near Taiwan. The first earthquake happened at 20:26 (UTC+8) (Academia Sinica, n.d.a), and the second one at 20:34 (UTC+8) (Academia Sinica, n.d.b). Fortunately, the earthquakes took place under the sea and the cities in TW were not heavily damaged, as happened in 1999. However, these two earthquakes did cause landslides over a wide area on the seabed near the Taiwan island. At 04:00 (UTC+9) on December 27th 2006, that is, after the second earthquake, the R&E networks in the Asian area were shutdown. The cable companies investigated the reason for the lost connection and found that the earthquake had caused damage to the cable systems.

Fig. 4. Fiber cut area around Taiwan island (Konishi, 2007)

The circle in Fig. 4 shows the area where the cable systems were cut off. Most of the fiber cables in the eastern Asia area went through southwestern Taiwan. These cables were generally bought and shared by different telecom companies.

## **4.2 Internet disconnections and lost BGP peerings**

After the earthquake, both commodity Internet traffic and R&E traffic were cut off. For instance, the JP-PH, JP-CN, JP-SG, CN-US, HK-KR, TW-(HK+CN), and TW-SG connections were lost. That is, the R&E network communities were divided into two groups. One was the group that consisted of JP, KR, TW, and US, and the other consisted of CN, HK, VN, MY, TH, SG, ID, and PH (Fig 5).

Fig. 5. Splitted R&E networks in Asia Pacific area

The Internet disconnection occurred in the following order.


366 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

On December 26th, 2006 (UTC+9) there were two huge earthquakes near Taiwan. The first earthquake happened at 20:26 (UTC+8) (Academia Sinica, n.d.a), and the second one at 20:34 (UTC+8) (Academia Sinica, n.d.b). Fortunately, the earthquakes took place under the sea and the cities in TW were not heavily damaged, as happened in 1999. However, these two earthquakes did cause landslides over a wide area on the seabed near the Taiwan island. At 04:00 (UTC+9) on December 27th 2006, that is, after the second earthquake, the R&E networks in the Asian area were shutdown. The cable companies investigated the reason for the lost connection and found that the earthquake had caused damage to the cable systems.

**4. Network failures caused by Taiwan earthquake** 

Fig. 4. Fiber cut area around Taiwan island (Konishi, 2007)

generally bought and shared by different telecom companies.

**4.2 Internet disconnections and lost BGP peerings** 

The circle in Fig. 4 shows the area where the cable systems were cut off. Most of the fiber cables in the eastern Asia area went through southwestern Taiwan. These cables were

After the earthquake, both commodity Internet traffic and R&E traffic were cut off. For instance, the JP-PH, JP-CN, JP-SG, CN-US, HK-KR, TW-(HK+CN), and TW-SG connections were lost. That is, the R&E network communities were divided into two groups. One was

**4.1 Fiber breaks** 

3. Automatic BGP re-routing along the alternative peer if any

Fig. 6. Traffic weather map on Dec.27 2006

Experience with Restoration of Asia Pacific Network Failures from Taiwan Earthquake 369

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

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

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

Fig. 8. Traffic between JP and KR on Dec.27 (UTC+9)}

Fig. 9. Traffic between JP and PH on Dec.27 (UTC+9)

eastbound routes, and that APAN-JP (JP) lost connectivity to TEIN2.

US. The direct link between CSTNET (CN) and US was also damaged.

routing policy that does not choose the route through KR.

**4.4 Changes of BGP routing tables** 

Figure 6 shows the Internet traffic weather map at APAN Tokyo XP (APAN-JP, n.d.), which displays connectivity and link utilization in real time. In Fig. 6 it can be observed that the JP-HK-CN, JP-TH, JP-SG, and JP-PH communications were lost and that there was 0% link utilization except a 100 Mbps load between JP and KR.

The link-layer disconnection caused BGP sessions to expire. BGP peerings from JP to HK+CN, TH, SG, and PH were lost and automatically diverted to detour routes.

In general, when traffic is transferred to the detour AS routes, the traffic will flow along the longer AS path rather than the usual one, because the shortest AS path will be selected as the primary AS path according to BGP policy.

Fig. 7. Number of IP prefixes that experienced AS path changes (2006.12.26 - 2006.12.27 at QGPOP)

Figure 7 shows the AS path changes of each IP prefix observed just after earthquake from the QGPOP (Kyushu GigaPOP Project [QGPOP], n.d.) BGP router in JP. It can be seen in Fig. 7 that more than 1000 IP prefixes experienced AS path changes after the earthquake.

#### **4.3 Traffic load changes**

Fortunately, despite the earthquake, the CN-KR and KR-JP cables were unbroken. Therefore, we were able to observe the detour traffic along these links due to BGP rerouting.

Figure 8 shows the traffic between JP and KR on Dec. 27th, 2006. At about 04:30 (UTC+9) the inbound traffic pattern between JP and KR had changed dramatically. At the same time, as can be seen in Fig. 9, the traffic between JP and PH disappeared.

The reason for the traffic change could be inferred from the routing policy of APAN Tokyo XP. The route from CN to JP through KR was one of the lowest priority routes, but after the earthquake, it was chosen because there were no available BGP routes with high priorities.

Fig. 8. Traffic between JP and KR on Dec.27 (UTC+9)}

Figure 6 shows the Internet traffic weather map at APAN Tokyo XP (APAN-JP, n.d.), which displays connectivity and link utilization in real time. In Fig. 6 it can be observed that the JP-HK-CN, JP-TH, JP-SG, and JP-PH communications were lost and that there was 0% link

The link-layer disconnection caused BGP sessions to expire. BGP peerings from JP to

In general, when traffic is transferred to the detour AS routes, the traffic will flow along the longer AS path rather than the usual one, because the shortest AS path will be selected as

Fig. 7. Number of IP prefixes that experienced AS path changes (2006.12.26 - 2006.12.27 at

that more than 1000 IP prefixes experienced AS path changes after the earthquake.

can be seen in Fig. 9, the traffic between JP and PH disappeared.

Figure 7 shows the AS path changes of each IP prefix observed just after earthquake from the QGPOP (Kyushu GigaPOP Project [QGPOP], n.d.) BGP router in JP. It can be seen in Fig. 7

Fortunately, despite the earthquake, the CN-KR and KR-JP cables were unbroken. Therefore, we were able to observe the detour traffic along these links due to BGP re-

Figure 8 shows the traffic between JP and KR on Dec. 27th, 2006. At about 04:30 (UTC+9) the inbound traffic pattern between JP and KR had changed dramatically. At the same time, as

The reason for the traffic change could be inferred from the routing policy of APAN Tokyo XP. The route from CN to JP through KR was one of the lowest priority routes, but after the earthquake, it was chosen because there were no available BGP routes with high

HK+CN, TH, SG, and PH were lost and automatically diverted to detour routes.

utilization except a 100 Mbps load between JP and KR.

the primary AS path according to BGP policy.

QGPOP)

routing.

priorities.

**4.3 Traffic load changes** 

Fig. 9. Traffic between JP and PH on Dec.27 (UTC+9)
