BGP updates

[Maham1530]

Hi,

I am working on a topology which has 6 AS systems. BGP is running between AS systems. The topology is not connected to any external network (internet/ISP).

I want to get BGP updates every minute. When I run the topology, I get BGP updates initially, just one time. After that there are no updates. Can anyone help me in figuring out how can I get updates every minute? 

I understand that updates are sent when there is some change in the topology. How can I make changes in topology every minute to get updates.

I am a newbie in networking stuff. Please help!

[Georg Pauwen]

Hello,

on one of your routers, you could create a loopback interface and then use an EEM script that runs every 60 seconds to advertise that network, hence triggering a topology change every 60 seconds. The script would look like below:

interface loopback100
ip address 100.100.100.100 255.255.255.255
!
event manager applet BGP_UPDATE
event timer watchdog time 60
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "router bgp 1"
action 4.0 cli command "network 100.100.100.100 mask 255.255.255.255"
action 5.0 wait 10
action 6.0 cli command "no network 100.100.100.100 mask 255.255.255.255"
action 7.0 cli command "end"

[Maham1530]

Hello,

Thanks a lot for the help!

I did similar to what you suggested. When ever there is an update, the dump file( where the updates are being saved) re write all the data every time. I don't know why this is happening. Every time I parse that file, there is only latest update and all the previous data is gone.

Can you help regarding this? 

Thanks.

[paul driver]

Hello

@Georg Pauwen  Why would you do this?, This will cause basically a route flap, network convergence and flood the bgp network with update messages thus making the network unstable!, imagine if you were receiving a full rib table?, Bgp even has a feature to dampen routes that flap consistently - So I would say the less updates the more stable bgp will be? 

[MHM Cisco World]

Check this command 

[paul driver]

Hello
Why do you want bgp updates every 60 seconds, not sure I understand?
FYI- When two bgp speakers establish a peering a full bgp table is initially exchanged between them, There after just incremental updates are sent out ONLY as/when there is a change in the route table?

[Maham1530]

Hello @paul driver 

Thanks for the reply. It is quite helpful.

I want to generate BGP data in my topology and this data is based on BGP Updates. This is the reason why I want BGP updates every minute.

Do you know any other way to generate bgp data without flapping?

[Giuseppe Larosa]

Hello @Maham1530 ,

as noted by Paul Driver you are working with BGP not with RIPv2.

BGP is based on TCP so there is no need of new updates until something changes in the state of an advertised prefix or a new prefix has to be advertised.

This capability of BGP is very important and is one the key elements that allow BGP to deal with 700,000 internet routes or more.

You can build a lab as suggested by @Georg Pauwen , but actually you are not forcing BGP to send updates every 60 seconds but only the affected prefix will be alternatively withdrawed or added.

This also explains what you see in the packet capture it is just an incremental update about the flapping prefix all other prefixes are not advertised anymore.

All this is correct and expected.

Hope to help

Giuseppe