The purpose of this example is to demonstrate the IP anycast feature. We will use the emulator from example-B00 as the base. The IP anycast technology allows multiple computers on the Internet to have the same IP address. When another machine sends a packet to this IP address, one of the computers will get the packet. Exactly which one will get the packet depends on BGP routing. IP anycast is naturally supported by BGP.
One of the well-known applications of IP anycast is the DNS root servers.
Some of the DNS root servers, such as the F server,
have multiple machines geographically located in many different places around the world,
but they have the same IP address.
For example, all the F servers have the same IP address 192.5.5.241.
When a DNS client sends a request to this
IP address, one of the F servers will get the request.
We will first create an autonomous system (AS-180). We create two networks
inside this AS, but we give them the same network prefix. We also create
a host on each network, and assign the same IP address to them.
as180 = base.createAutonomousSystem(180)
as180.createNetwork('net0', '10.180.0.0/24')
as180.createNetwork('net1', '10.180.0.0/24')
as180.createHost('host-0').joinNetwork('net0', address = '10.180.0.100')
as180.createHost('host-1').joinNetwork('net1', address = '10.180.0.100')
It should be noted that this AS has two disjoint parts: one has net0, and the
other has net1. These two networks are not connected by any router.
We then connect one part of the AS to ix100, and connect the other part
of the AS to ix105, and peer the AS with other ASes at these two locations.
as180.createRouter('router0').joinNetwork('net0').joinNetwork('ix100')
ebgp.addPrivatePeerings(100, [3, 4], [180], PeerRelationship.Provider)
as180.createRouter('router1').joinNetwork('net1').joinNetwork('ix105')
ebgp.addPrivatePeerings(105, [2, 3], [180], PeerRelationship.Provider)
When compiling the emulation to generate the docker files, we need
to set the selfManagedNetwork option to True. Without this option,
the network will be entirely managed by Docker, which will not
allow us to have two networks with the same IP prefix. Using
this option will solve this problem.
emu.compile(Docker(selfManagedNetwork=True), './output')
Now, we have deployed two hosts using the IP anycast technology.
When other machines send a packet to 10.180.0.100, one of these two
hosts will get the packet.
We can ping 10.180.0.100 from one of the hosts in the emulator,
we set the filter to icmp. We should be able to see the
traffic going to one of the 10.180.0.100 hosts. If we disable
this location's BGP session, we will see that the traffic
immediately switches to the other 10.180.0.100 host.
We should also be able to find two hosts inside the emulator,
such that they talk to a different 10.180.0.100 host.
We can run a UDP server on each of the 10.180.0.100 host using nc -luk 9090.
Then from another machine, we send a UDP message to 10.180.0.100.
One of the hosts will receive the message, depending on where the client
is located. If we disable the BGP session at one of the locations,
we can see that the UDP message will go to the other server.
# echo hello | nc -u 10.180.0.100 9090