When the router starts to receive the prefix at the time of initialization, the path selection process has been run in advance, which will cause the best path to keep changing, so that multiple updates of the same prefix will be sent, which is inefficient.
Enable read-only mode to reduce CPU and network usage when restarting the BGP process. When applicable, read-only mode would begin as soon as the first peer reaches Established status and a timer for maximum delay seconds is started. During this mode BGP doesn’t run any best-path or generate any updates to its peers. This mode continues until either of the following two conditions are met:
1. All the configured peers, except the shutdown peers, have sent explicit EOR (End-Of-RIB) or an implicit- EOR. The first keep-alive after BGP has reached Established is considered an implicit-EOR. If the establish-wait optional value is given, then BGP will wait for peers to reach established from the beginning of the update-delay till the establish-wait period is over, i.e. the minimum set of established peers for which EOR is expected would be peers established during the establish-wait window, not necessarily all the configured neighbors.
2. maximum delay period is over.
On hitting any of the above two conditions, BGP resumes the decision process and generates updates to its peers.
Default maximum delay is 0, i.e. the read-only mode is disabled by default.
Note that the establish-wait setting is optional; however, if specified, it must be shorter than the maximum delay timer.
The following example commands enable read-only mode by setting the maximum delay timer to 500 seconds and the establish-wait timer to 90 seconds.