Overview

BGP applies triggered updates that send routes when there is some kind of change. The minimum advertisement interval slightly delays the advertisement of BGP routes when changes occur.

This section describes the commands for configuring the minimum advertisement interval for BGP routes.

What is the minimum advertisement interval?

BGP sends route information when changes occur due to triggered updates. However, instead of sending route information immediately after a change occurs, the route information is delayed by a minimum advertisement interval. This reduces the impact of route flaps.

The default value of the minimum advertisement interval for route information are as follows

  • IBGP neighbor : 5sec
  • EBGP neighbor : 30sec

BGP route minimum advertisement interval configuration command

To change the minimum advertisement interval for BGP routes, enter the following command in BGP configuration mode

minimum advertisement interval configuration

(config)#router bgp <AS>
(config-router)#neighbor <ip-address> advertisement-interval <interval>

<AS>:AS number
<ip-address>: neighbor IP address
<interval>: minimum advertisement interval (sec)

The minimum advertisement interval can be checked with the show ip bgp neighbor command.

show ip bgp neighbor verify minimum advertisement interval

R1#show ip bgp neighbors
BGP neighbor is 172.16.1.11,  remote AS 1, external link
  BGP version 4, remote router ID 111.1.1.11
  BGP state = Established, up for 00:13:48
  Last read 00:00:27, hold time is 150, keepalive interval is 50 seconds
  Neighbor capabilities:
    Route refresh: advertised and received(old & new)
    Address family IPv4 Unicast: advertised and received
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
                         Sent       Rcvd
    Opens:                  2          2
    Notifications:          0          0
    Updates:                0          2
    Keepalives:            44         46
    Route Refresh:          0          0
    Total:                 46         50
  Default minimum time between advertisement runs is 30 seconds
-- omitted --

BGP route minimum advertisement interval configuration example

Verify the minimum advertisement interval for BGP routes in the following network diagram.

Figure minimum advertisement interval configuration network diagram
Figure minimum advertisement interval configuration network diagram

Use the show ip bgp neighbor command on R1 to verify the default minimum advertisement interval.

R1 show ip bgp neighbors

R1#show ip bgp neighbors 3.3.3.3
BGP neighbor is 3.3.3.3,  remote AS 100, internal link
  BGP version 4, remote router ID 3.3.3.3
  BGP state = Established, up for 00:01:35
  Last read 00:00:35, hold time is 180, keepalive interval is 60 seconds
  Neighbor capabilities:
    Route refresh: advertised and received(old & new)
    Address family IPv4 Unicast: advertised and received
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
                         Sent       Rcvd
    Opens:                  3          2
    Notifications:          0          2
    Updates:                1          0
    Keepalives:             5          4
    Route Refresh:          0          0
    Total:                  9          8
  Default minimum time between advertisement runs is 5 seconds
-- omitted --
R1#show ip bgp neighbors 172.16.1.11
BGP neighbor is 172.16.1.11,  remote AS 1, external link
  BGP version 4, remote router ID 111.1.1.11
  BGP state = Established, up for 00:25:33
  Last read 00:00:33, hold time is 150, keepalive interval is 50 seconds
  Neighbor capabilities:
    Route refresh: advertised and received(old & new)
    Address family IPv4 Unicast: advertised and received
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
                         Sent       Rcvd
    Opens:                  2          2
    Notifications:          0          0
    Updates:                0          2
    Keepalives:            58         60
    Route Refresh:          0          0
    Total:                 60         64
  Default minimum time between advertisement runs is 30 seconds
-- omitted --

R3 is an IBGP neighbor, so it is 5 seconds, and ISP1 is an EBGP neighbor, so it is 30 seconds. Then, on R1, change the minimum advertisement interval.

R1 change minimum advertisement interval

router bgp 100
 neighbor 3.3.3.3 advertisement-interval 10
 neighbor 172.16.1.11 advertisement-interval 35

After configuration, use the show ip bgp neighbor command to verify the value of the minimum advertisement interval.

R1 show ip bgp neighbors 

R1#show ip bgp neighbors 3.3.3.3
-- omitted --

 For address family: IPv4 Unicast
  BGP table version 5, neighbor version 5
  Index 1, Offset 0, Mask 0x2
  NEXT_HOP is always this router
                                 Sent       Rcvd
  Prefix activity:               ----       ----
    Prefixes Current:               4          0
    Prefixes Total:                 4          0
    Implicit Withdraw:              0          0
    Explicit Withdraw:              0          0
    Used as bestpath:             n/a          0
    Used as multipath:            n/a          0

                                   Outbound    Inbound
  Local Policy Denied Prefixes:    --------    -------
    Total:                                0          0
  Number of NLRIs in the update sent: max 3, min 0
  Minimum time between advertisement runs is 10 seconds
-- omitted --
R1#show ip bgp neighbors 172.16.1.11
-- omitted --

 For address family: IPv4 Unicast
  BGP table version 5, neighbor version 5
  Index 2, Offset 0, Mask 0x4
                                 Sent       Rcvd
  Prefix activity:               ----       ----
    Prefixes Current:               1          3 (Consumes 144 bytes)
    Prefixes Total:                 2          3
    Implicit Withdraw:              1          0
    Explicit Withdraw:              0          0
    Used as bestpath:             n/a          3
    Used as multipath:            n/a          0

                                   Outbound    Inbound
  Local Policy Denied Prefixes:    --------    -------
    Bestpath from this peer:              6        n/a
    Total:                                6          0
  Number of NLRIs in the update sent: max 1, min 0
  Minimum time between advertisement runs is 35 seconds
-- omitted --

For each, you can see that the minimum advetisement interval has changed as configured.

Summary

Point

  • The minimum advertisement interval allows for a small delay when advertising a BGP route upon some change.
  • The default minimum advertisement interval is as follows
    • EBGP neighbor : 30sec
    • IBGP neighbor : 5sec
  • To change the minimum advertisement interval, enter the following command in BGP configuration mode
    • (config)#router bgp <AS>
      (config-router)#neighbor <ip-address> advertisement-interval <interval>

How the BGP works