Context
Configuring the BGP next hop delayed response can speed up BGP route convergence and
minimize traffic loss.
As shown in Figure 7-3, PE1, PE2, and PE3 are the clients of the RR. CE2 is dual-homed to
PE1 and PE2. PE1 and PE2 advertise their routes to CE2 to the RR. The RR advertises the route
from PE1 to PE3. PE3 has a route to CE2 only and advertises this route to CE1. After the route
exchange, CE1 and CE2 can communicate. If PE1 fails, PE3 detects that the next hop is
unreachable and instructs CE1 to delete the route to CE2. Traffic is interrupted. After BGP route
convergence is complete, the RR selects the route advertised by PE2 and sends a route update
message to PE3. PE3 then advertises this route to CE1, and traffic forwarding is restored to the
normal state. A high volume of traffic will be lost during traffic interruption because BGP route
convergence is rather slow.
If the BGP next hop delayed response is enabled on PE3, PE3 does not reselect a route or instruct
CE1 to delete the route to CE2 immediately after detecting that the route to PE1 is unreachable.
After BGP convergence is complete, the RR selects the route advertised by PE2 and sends the
route to PE3. PE3 then reselects a route and sends a route update message to CE1. Traffic
forwarding is restored to the normal state. After the BGP next hop delayed response is enabled
on PE3, PE3 does not need to delete the route or instruct CE1 to delete the route. This delayed
response speeds up BGP route convergence and minimizes traffic loss.
Figure 7-3 Networking diagram for configuring the BGP next hop delayed response
The BGP next hop delayed response applies to a scenario where the next hop has multiple links
to reach the same destination. If there is only one link between the next hop and the destination,
configuring the BGP next hop delayed response may cause heavier traffic loss when the link
fails because link switching is impossible.
Pre-configuration Tasks
Before configuring the BGP next hop delayed response, complete the following task:
l Configuring Basic BGP Functions
S6700 Series Ethernet Switches
Configuration Guide - IP Routing 7 BGP Configuration
Issue 01 (2012-03-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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