Control BGP Advertisements to eBGP peers with ExaBGP

This entry is part 5 of 6 in the series Influence Routing Decisions with python and ExaBGP

We know that ExaBGP can be used to inject BGP routes into an AS that you control. It’s a very helpful feature that allows you to automate reachability and traffic flows within your network. But what if you want to you ExaBGP to influence what is advertised, or in this case, not advertised to external peers that are not willing to peer with your ExaBGP service?

BGP PeeringsOur scenario is this: We have a 100.10.10.0/24 prefix attached to our SW. The CE router learns about this prefix from SW via OSPF, and then advertises the prefix out to the Internet via the PE router. This 100.10.10.0/24 prefix is anycasted so it is also advertised out of a different location. In order to withdraw the prefix from the PE and therefore the Internet we would need to manually filter the prefix outbound via route-map, or stop the advertisement from the SW which would also remove the resource from local resources. Continue reading

Give ExaBGP an HTTP API with SimpleHTTPServer or Flask

This entry is part 3 of 6 in the series Influence Routing Decisions with python and ExaBGP

We’ve covered how to setup ExaBGP and peer with a router, and then how to use python to add  and remove advertised routes in BGP either with static definitions or dynamically through health checking. There may be some of you out there with some sort of application that is already monitoring routes and you’re trying to figure out how to connect it with ExaBGP for the actual interaction part? Well, what if we add an HTTP API to ExaBGP to give programmatic access to ExaBGP from some external utility? I’ll go over two ways to do this using the python built-in SimpleHTTPServer or Flask.

Using SimpleHTTPServer

This option is great since you don’t need to install any extra modules. It seems to be pretty lightweight and should be enough for some basic HTTP interaction with ExaBGP. The basic functions that we need this API to do are receive a form via HTTP POST and print that to STDOUT. Since ExaBGP is executing the python script, the STDOUT output will be visible to the ExaBGP process. After the ExaBGP command is printed, we’ll return the command to the browser as confirmation that the call was successful. Here’s the example:

Using Flask

If you have bigger plans for the HTTP side of things and want to work with a web framework like Flask, this example is for you. The biggest difference is that you will have to install Flask and its dependencies, although that’s easy:

$ pip install flask

Now we’ll create a Flask http_api.py file to listen for prefix commands via HTTP POST calls and print them to STDOUT so ExaBGP can do its magic:

Before you run off and put this on your production systems I have a couple disclaimers:

  • This script uses the built-in Flask debug HTTP server. It’s fine for lab use, but I would use gunicorn and nginx for real heavy lifting.
  • The script doesn’t do any validation of the command. A better script would make sure it’s a valid command and prefix.
  • Flask defaults to listening on the localhost address on TCP port 5000. You can change this though and I highly recommend reading Flask’s QuickStart article to familiarize yourself with the many options.

Hooking the HTTP API up to the ExaBGP process

Update the conf.ini file to run this script instead of our previous health check example:

And now when we run $ exabgp conf.ini, you’ll see the confirmation of running the python script at the end of the output, along with the debug output of both Flask or SimpleHTTPServer:

Once either HTTP service is running (somewhat wrapped by the ExaBGP process), we can make HTTP POST calls via command line (curl, wget) or via a GUI HTTP tool (Postman). I’ll show a quick example of both:

Curl:

Postman:Postman - HTTP POST

 

When we run show bgp on the router, we can see our advertised network:

So, there’s a real quick and dirty way to allow external calls to ExaBGP for your RIB manipulation. The next post will cover more advanced peering and advertising options with ExaBGP.

Using service health checks to automate ExaBGP

This entry is part 2 of 6 in the series Influence Routing Decisions with python and ExaBGP

If you haven’t read the intro post to this series, Getting Started with ExaBGP, check that article out first as this post will be expanding on the previous example to show how to use python for more automated interaction with ExaBGP.

The first example I’ll cover is using a basic health check test to determine if a route should be announced or withdrawn from BGP. Here is our python script healthcheck.py with comments inline:

Continue reading

ExaBGP and python: Getting Started

This entry is part 1 of 6 in the series Influence Routing Decisions with python and ExaBGP

I’m really excited about these next few posts. I’ve been doing some research on BGP and automating routing decisions with python, which led to my discovery of ExaBGP. ExaBGP is dubbed “The BGP swiss army knife”, and I’m early in my experimentation with this tool, but it seems to be a very easy way to peer with your BGP routers and control the advertisement of networks.

This post will cover basic setup of ExaBGP and peering with a router, as well as how you can tie in python to present control for the advertisement of routes. The next post will use the Flask web framework to offer a simple HTTP API for adding/removing routes. I hope the following posts will be along the lines of receiving the BGP UPDATE messages from peered routers to monitor and analyze advertised networks.

Continue reading