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To explore the configuration of BGP, let us consider a network that contains three ASes: ``AS1``, ``AS2`` and ``AS3``. To simplify the tests, we identify one host inside each of these ASes.
 
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Exploring BGP
 
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The packet traces collected on the three routers of this example are available from :download:`/exercises/traces/ripng-r1-trace.pcap`, :download:`/exercises/traces/ripng-r2-trace.pcap` and :download:`/exercises/traces/ripng-r3-trace.pcap`.
 
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Later, router ``r2`` will regularly transmit its distance vector inside an unsolicited response message that is sent towards the IPv6 multicast address ``ff02::9``.
 
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Router ``r2`` receives a similar request from ``fe80::481a:48ff:fed7:292e`` and replies by sending its routing table in a response message. Note that this message is sent to the link-local address of the requesting router.
 
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When a router starts, it sends a request message. This is illustrated in the figure below with the first message sent by router ``r2``. This message is sent inside an IPv6 packet whose source address is the link-local address of the router and the destination address is ``ff02::9`` which is the reserved multicast address for RIPng.
 
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the responses that contain the router's routing table
 
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the requests
 
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We can observe the RIPng messages that are exchanged over the network. :rfc:`2080` defines two types of RIPng messages:
 
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As RIP messages are exchanged using UDP on port 521, we filter this port in the tcpdump_ trace. RIPng distributes the routes and our two hosts can exchange packets. The entire script is available from :download:`/exercises/ipmininet_scripts/ripng.py`.
 
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IPMininet_ can also be used to perform experiments with RIP. A simple script that uses RIPng is provided below.
 
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Exploring RIP
 
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A more detailed discussion of the packets that routing protocols exchange may be found in [Goralski2009]_.
 
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OSPFv3 also includes `LS Acknowledge` packets that acknowledge the correct reception of link state information.
 
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The requested information is sent in a `LS Update` packet shortly after that.
 
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Router ``r2`` reacts to this updated Database description packet by requesting the link state information that it does not already know. For this, it sends a `LS Request` packet.
 
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This packet is updated when new information is added in the router's OSPFv3 database. A few seconds router, this router sends another Database description packet that announces more information.
 
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We can then observe the Database description packet that is sent by routers to announce the state of their OSPFv3 database. The details of this packet are beyond the scope of this simple exercise.
 
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The Hello packet contains some parameters such as the `Hello interval` that is set to 1 second. This interval is the delay between the transmission of successive Hello packets. Since the `Router Dead Interval` is set to 3 seconds, the router will consider the link as down if it does not receive Hello packets during a period of 3 seconds. The second packet of the trace is sent by router ``r1``.
 
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The first packet that this router received his a Hello packet that was sent by router ``r2``. There are several interesting points to note about this packet. First, its source address is the link-local address (``fe80::68bc:b4ff:fe19:42b7``) of router ``r2`` on this interface. The destination address of the packet is reserved IPv6 multicast address for OSPFv3, i.e. ``ff02::5``. The Hop Limit of the packet is set to 1 and OSFPv3 uses a next header of type 89.
 
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