How often will the routing table be synchronized between two routers using EBGP over a single T1 link?

The synchronization of the routing table in a scenario using External Border Gateway Protocol (EBGP) occurs specifically when an update message is received. EBGP is designed to exchange routing information between different autonomous systems, and its operation is based on the exchange of BGP update messages that contain route advertisements.

When a router receives an update message, it processes the information within that message, which may include new routes, withdrawn routes, or path attributes. This processing results in the routing table being updated in real-time, allowing routers to adapt to changes in the network topology or fluctuations in available routes. The asynchronous nature of BGP means that changes in routing information are propagated only when there are updates, making this method both efficient and effective.

The other choices suggest periodic synchronization or synchronization based on certain messages, which does not accurately reflect how EBGP operates. EBGP's reliance on update messages emphasizes its efficient use of bandwidth and responsiveness to network changes rather than periodic checks or notifications.