Huawei Quidway NetEngine80E Configuration Manual page 982

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
If routes carry Originator_ID attributes, the Originator_ID attributes (rather than router IDs) are
compared.
Router ID
If multiple routes to the same destination are available, BGP preferentially selects the route
advertised by the device with the smallest router ID.
A router ID uniquely identifies a router in an AS, and the router ID can be configured as follows:
l
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If each route carries an Originator_ID, the Originator_IDs rather than router IDs are compared
during route selection. The route with the smallest Originator_ID is preferred. By default,
Cluster_List takes precedence over Originator_ID during BGP route selection. To enable
Originator_ID to take precedence over Cluster_List during BGP route selection, run the
bestroute router id-prior-clusterlist command.
For more router ID-based route selection examples, see Local_Pref, Origin, and MED.
Peer IP Address
BGP prefers the route learned from the peer with the smallest IP address during BGP route
selection.
The peer IP address is the IP address specified in ipv4-address or ipv6-address in the peer
{ group-name | ipv4-address | ipv6-address } as-number { as-number-plain | as-number-dot }
command. The group-name parameter specified in the command is the one specified in the
peer { ipv4-address | ipv6-address } group group-name command.
If the optimal route has not been selected yet before BGP begins to compare peer IP addresses,
the local device may have established multiple BGP peer relationships with another device
through equal-cost links. In most cases, if a backup physical link is available between two
devices, using loopback interfaces to establish a BGP peer relationship is recommended although
multiple BGP peer relationships may be established between the two devices through the
physical links.
In Figure
Router B can use loopback interfaces to establish a BGP peer relationship or use the two links
to establish two BGP peer relationships. In the following example, the two links are used to
establish two BGP peer relationships to show how peer addresses are used in route selection.
Issue 02 (2014-09-30)
Run the router-id { ipv4-address | vpn-instance auto-select } command. If no router ID
is configured in the BGP view, BGP selects a router ID configured in the system view. For
details on how a router ID configured in the system view is selected, see router-id.
Run the router-id (BGP) { ipv4-address | auto-select } command in the BGP VPN instance
IPv4/IPv6 address family view. The router-id (BGP VPN instance IPv4/IPv6 address
family view) command takes precedence over the router-id (BGP) command.
8-28, two physical links are available between Router A and Router B. Router A and
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