cnp3-ebook/exercises/routing-protocols

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63 ../../exercises/routing-protocols.rst:861

	English The ``UPDATE`` message can be used to withdraw and advertise routes. The packet below is sent by ``AS2`` to advertise its route towards `2001:cafe:2::/48` on the BGP session with ``AS1``. 187/10000 · 187
64 ../../exercises/routing-protocols.rst:866

	English Another interesting utilization of IPMininet_ is to explore how routers react to link failures. We start from the same network as with the previous example and disable the link between ``AS2`` and ``AS3``. For this, we log on one of the two routers and issue the following commands. 282/10000 · 282
65 ../../exercises/routing-protocols.rst:898

	English We first connect to the BGP daemon on router `as2`. In addition to the `show` commands that have been described earlier, the router also supports privileged commands that can change its configuration. Before executing these commands, we must enter the privileged mode with the `enable` command. On production routers, this command requires a password to verify the credentials of the network administrator. The `#` prompt indicates that we are allowed to execute privileged commands. We first check the state of the BGP sessions with the `show bgp summary` commands. There are two BGP sessions configured on this router. 620/10000 · 620
66 ../../exercises/routing-protocols.rst:900

	English We can now disable one of the BGP sessions on router `as2` as follows. 70/10000 · 70
67 ../../exercises/routing-protocols.rst:911

	English We start indicate that we will use the terminal to change the router configuration with `configure terminal`. We then enter the BGP part of the configuration with `router bgp 2` (`2` is the AS number of `as2`). Then we use the `neighbor 2001:cafe:2:23::3 shutdown` that takes as parameter the IP address of the peer of the session that we want to stop. We then leave the BGP part of the configuration (first `exit`) and the configuration menu (second `exit` command). At this point, the BGP session between ``AS2`` and ``AS3`` is down. 535/10000 · 535
68 ../../exercises/routing-protocols.rst:930

	English Without a BGP session between ``AS2`` and ``AS3``, there are reachability problems in this simple Internet. 107/10000 · 107
69 ../../exercises/routing-protocols.rst:941

	English We can fix them by enabling again the BGP session with the `no neighbor 2001:cafe:2:23::3 shutdown` command. 108/10000 · 108
70 ../../exercises/routing-protocols.rst:989

	English Exercises 9/10000 · 9
71 ../../exercises/routing-protocols.rst:991

	English We can use IPMininet_ to prepare some networks with problems that need to be analyzed and corrected. 100/10000 · 100
72 ../../exercises/routing-protocols.rst:993

	English Our first example is a small Internet with 5 ASes. A subset of the script that configures this network is shown below. There is one host attached to each AS and this host has the same number as its AS. The entire script is available from :download:`/exercises/ipmininet_scripts/ebgp-bug.py`. 291/10000 · 291
73 ../../exercises/routing-protocols.rst:1016

	English When this network is launched, `ping6all` reports connectivity problems. Hosts `h1` and `h4` cannot exchange packets. Can you fix the problem by changing the routing policy used on only one interdomain link ? Justify your answer 228/10000 · 228
74 ../../exercises/routing-protocols.rst:1029

	English Another interesting utilization IPMininet_ is to explore the impact of a link failure. We start from a small variant of the above topology. 139/10000 · 139
75 ../../exercises/routing-protocols.rst:1052

	English When this network starts, all hosts can reach all other hosts. 62/10000 · 62
76 ../../exercises/routing-protocols.rst:1066

	English Draw the network and try to predict how it will react to a shutdown of any of the customer-provider links ? 107/10000 · 107
77 ../../exercises/routing-protocols.rst:1068

	English What are the BGP messages that will be exchanged when the link between ``AS1`` and ``AS2`` fails ? How does this affect the reachability of the different hosts ? 161/10000 · 161
78 ../../exercises/routing-protocols.rst:1098

	English What are the BGP messages that will be exchanged when the link between ``AS1`` and ``AS3`` fails ? How does this affect the reachability of the different hosts ? 161/10000 · 161
79 ../../exercises/routing-protocols.rst:1128

	English What are the BGP messages that will be exchanged when the link between ``AS1`` and ``AS5`` fails ? How does this affect the reachability of the different hosts ? 161/10000 · 161
80 ../../exercises/routing-protocols.rst:1158

	English What are the BGP messages that will be exchanged when the link between ``AS3`` and ``AS4`` fails ? How does this affect the reachability of the different hosts ? 161/10000 · 161
81 ../../exercises/routing-protocols.rst:1190

	English Let us now consider another example. The network contains nine ASes with one host per AS. Assuming that ``AS9`` announces prefix `p9` and that ``AS2`` announces prefix `p2`. 173/10000 · 173
82 ../../exercises/routing-protocols.rst:1228

	English What is the Loc-RIB of ``AS6`` for prefix `p9` ? Indicate which is the best route towards this prefix. 102/10000 · 102

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