Analysis of BGP Route update Timer

BGP Route update timer analysis defines the BGP Route update timer on RFC4271 of BGP. This timer can only work for routes with the same prefix of the same address family, its main function is to prevent a route in the network from fluctuating too frequently, and it is also a protection for the CPU. It may be too obscure to describe this feature in text, so we will use a diagram for a brief introduction: www.2cto.com

Route update timer description
, The red and blue arrows represent routes with the same prefix, but learn from different neighbors, and the blue route is better than the red one. The black axis represents the time when the route was sent and received, each unit is 10 seconds away. We assume that the update timer configured on RA is 30 seconds. The RB route convergence process is as follows: www.2cto.com Ø RA sends the Red Route to RB immediately after receiving it, and starts the update timer (30 seconds) on RA ); Ø after 10 seconds, RA receives a better Blue Route. Because the timer does not time out, it is not sent to RB temporarily, but the local route table is updated, and route convergence is completed in 10th seconds; the update timer times out on RA in 30th seconds. Therefore, the blue route is sent to RB and the red route is updated. RB converges in 30th seconds. From the above analysis, we can see that the RB convergence time is about 20 seconds slower than that of RA. Because BGP is a delay from the vector routing protocol, it may affect the BGP router of the entire network, therefore, the design of this parameter must be considered in the design of BGP networks. If you have sufficient confidence in the routing and processing capabilities of your devices, you can set the value of this timer to a minimum value. Here, we need to note that there is a similar situation in the Dampening. If you want the network to converge as soon as possible after a route shock occurs, you can leave the Dampening parameter unspecified.