**5.1 Automatic BGP re-routing**

Usually, the full BGP routing table includes a few "useless" routes (Tbl. 2). By "useless" we mean that the route itself provides only connectivity with the long RTT and insufficient bandwidth. Therefore, the network operators filter out such useless routes by setting the local preference to ignore them. However, after the earthquake, these useless BGP routes worked automatically as backup paths. In the Asia Pacific R&E networks, the routes became very complicated after TEIN2 started because TEIN2 provided a few unexpected routes around the world. Because there were backup AS paths, automatic BGP re-routing could be used for first aid to provide the connectivity to the ASs that lost the primary paths. However, automatic BGP re-routing did not consider the traffic engineering parameters of the available bandwidth and the backup traffic load.


Table 2. Examples of the "useless routes"

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

Figure 18 shows the RTT between SG and JP just after the earthquake and the recovery

After the network failures caused by the earthquake, several restoration steps were taken to

Usually, the full BGP routing table includes a few "useless" routes (Tbl. 2). By "useless" we mean that the route itself provides only connectivity with the long RTT and insufficient bandwidth. Therefore, the network operators filter out such useless routes by setting the

Fig. 17. TEIN2 traffic was routed through SG and KR.

Fig. 18. RTT between SG and JP during the restoration process

restore communication. In this subsection, we discuss these steps.

**5. Network restoration methods** 

**5.1 Automatic BGP re-routing** 

process.
