Operation Manual – Routing ProtocolH3C S7500 Series Ethernet Switches Chapter 6 BGP Configuration6-9Caution:z A router must be assigned a router ID in order to run BGP protocol. A router ID is a32-bit unsigned integer. It uniquely identifies a router in an AS.z A router ID can be configured manually. If no router ID is configured, the systemwill automatically select an IP address from the IP addresses of the interfaces asthe router ID. A router ID is selected in the following way: if loopback interfaceaddresses are configured, the system chooses the latest configured IP address asthe router ID; if no loopback interface is configured, the first configured IP addressamong the IP addresses of other interfaces will be the router ID. For networkreliability consideration, you are recommended to configure the IP address of aloopback interface as the router ID.z Router IDs can be re-selected. A re-selected router ID takes effect only after theBGP process is restarted.z In order for route update packets to be sent even if problems occur on interfaces,you can configure the source interfaces of route update packets as a loopbackinterface.z Normally, EBGP peers are connected through directly connected physical links. Ifno such link exists, you need to use the peer ebgp-max-hop command to allowthe peers to establish multiple-hop TCP connections between them.6.4 Configuring the Way to Advertise/Receive RoutingInformation6.4.1 Configuration PrerequisitesMake sure the following operation is performed before configuring the way toadvertise/receive BGP routing information.z Enabling the basic BGP functionsMake sure the following information is available when you configure the way toadvertise/receive BGP routing information.z The aggregation mode and the aggregated routez Access list numberz Filtering direction (advertising/receiving) and the route policies to be adopted.z Route dampening settings, such as half-life and the thresholds.6.4.2 Importing RoutesWith BGP employed, an AS can send its interior routing information to its neighborASs. However, the interior routing information is not generated by BGP; it is obtained
