cnp3-ebook/exercises/ipv6 — English @ Weblate

Exit Zen

86 ../../exercises/ipv6.rst:796

	English Another useful command is ``xterm`` 'node' that allows to launch a terminal on the specified node. This gives you a interactive shell on any node. You can use it to capture packets with tcpdump_. As an example, let us use :manpage:`traceroute6(8)` to trace the path followed by packets from host ``a`` towards the IPv6 address of host ``b`` i.e. ``2001:db8:1341:3::b``. The output of this command shows that the path passes through routers ``r1``, ``r2`` and ``r3``. 466/10000 · 466
87 ../../exercises/ipv6.rst:808

	English Another interesting mininet_ command is ``pingall`` it allows to check that any host can reach any other host inside the network. It executes a ping from any host to any other host inside the network topology. 209/10000 · 209
88 ../../exercises/ipv6.rst:819

	English When debugging a network, it can be interesting to capture packets using tcpdump_ on specific links to check that they follow the expect. If you use tcpdump_ without any filter, you will capture the packets generated by xterm. To capture packets, you need to specify precise filters that will match the packets of interest. For traceroute6, you need to match the IPv6 packets that contain UDP segments and some ICMPv6 packets. The script below provides a simple filter that you can reuse. It takes one argument: the name of the interface on which tcpdump_ needs to run. 569/10000 · 569
89 ../../exercises/ipv6.rst:827

	English Starting from the :download:`/exercises/ipmininet_scripts/static-1.py` IPMininet_ script, we can explore classical problems when networks are configured with static routes. A first problem is when a router has an incomplete forwarding table. We configure the static routes as shown below. The entire script is available from :download:`/exercises/ipmininet_scripts/static-1-hole.py`. 383/10000 · 383
90 ../../exercises/ipv6.rst:841

	English We first check with ``pingall`` whether the network works correctly. 68/10000 · 68
91 ../../exercises/ipv6.rst:851

	English The problem can be detected by using :manpage:`traceroute6(8)`. 63/10000 · 63
92 ../../exercises/ipv6.rst:861

	English In the output of :manpage:`traceroute6(8)`, a ``!N`` indicates that host ``a`` received from ``2001:db8:1341:12::2``, i.e. router ``r2``, a Network unreachable ICMPv6 message. The forwarding table of ``r2`` confirms the root cause of this problem. 247/10000 · 247
93 ../../exercises/ipv6.rst:873

	English A second problem is when there is a forwarding loop inside the network, i.e. packets sent to a specific destination loop through several routers. With the static routes shown below, router ``r2`` forwards the packets towards ``2001:db8:1341:3::b`` via router ``r1``. The entire script is available from :download:`/exercises/ipmininet_scripts/static-1-loop.py`. 361/10000 · 361
94 ../../exercises/ipv6.rst:888

	English The ``pingall`` command reveals that there is a problem in this network. 72/10000 · 72
95 ../../exercises/ipv6.rst:898

	English We can analyze this configuration problem in more details by using ``traceroute6``. The loop appears clearly. 109/10000 · 109
96 ../../exercises/ipv6.rst:919

	English On host ``b``, the problem is different. The packets that it sends towards host ``a`` do not seem to go beyond router ``r3``. 125/10000 · 125
97 ../../exercises/ipv6.rst:933

	English To debug this problem, let us look at the forwarding table of ``r3``. This router forwards the packets sent to host ``a`` to router ``r1`` that is directly connected to host ``a``. 180/10000 · 180
98 ../../exercises/ipv6.rst:946

	English Unfortunately, when router ``r1`` sends its ICMP HopLimit exceeded message, the destination of this IP packet is ``2001:db8:1341:3::b``. This packet is forward to router ``r2`` that returns the packet back to router ``r1``. The packet loops between the two routers until their HopLimit reaches zero. 299/10000 · 299
99 ../../exercises/ipv6.rst:965

	English IPv6 packets 12/10000 · 12
100 ../../exercises/ipv6.rst:967

	English To correctly understand the operation of IPv6, it is sometimes important to remember the packet format and how the different fields are used. 141/10000 · 141
101 ../../exercises/ipv6.rst:971

	English The `Next Header` of the IPv6 packet indicates the type of the header that follows the IPv6 packet. IANA_ maintains a list of all the assigned values of this header at https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml 240/10000 · 240
102 ../../exercises/ipv6.rst:980

	English When an IPv6 router receives a packet that is larger than the Maximum Transmission Unit (MTU) on its outgoing interface, it drops the packet and returns an ICMPv6 message back to the source. Upon reception of this ICMPv6 message, the source will either adjust the size of the packets that it transmits or use IPv6 packet fragmentation. The exercises below show a few examples of the utilization of IPv6 fragmentation. 417/10000 · 417
103 ../../exercises/ipv6.rst:987

	English Network engineers often rely on :manpage:`ping6(8)` to verify the reachability of a remote host or router. :manpage:`ping6(8)` sends ICMPv6 echo request messages and analyzes the received ICMPv6 echo responses. Each echo request message contains an identifier and a sequence number that is returned in the response. 316/10000 · 316
104 ../../exercises/ipv6.rst:991

	English When the :manpage:`ping6(8)` is executed, it sends ICMPv6 echo request messages with increasing sequence numbers. 113/10000 · 113
105 ../../exercises/ipv6.rst:995

	English The :manpage:`traceroute6(8)` software is very useful to debug network problems. It sends a series of UDP segments encapsulated inside IP packets with increasing values of the HopLimit. The first packet has a HotLimit and the first router on the path returns an ICMPv6 HopLimit exceeded message. 295/10000 · 295

Shortcut	Action
`?`	Open available keyboard shortcuts.
`Alt` + `Home`	Navigate to the first translation in the current search.
`Alt` + `End`	Navigate to the last translation in the current search.
`Alt` + `PageUp` or `Ctrl` + `↑` or `Alt` + `↑` or `Cmd` + `↑` or	Navigate to the previous translation in the current search.
`Alt` + `PageDown` or `Ctrl` + `↓` or `Alt` + `↓` or `Cmd` + `↓` or	Navigate to the next translation in the current search.
`Ctrl` + `Enter` or `Cmd` + `Enter`	Submit current form; this works the same as pressing Save and continue while editing translation.
`Ctrl` + `Shift` + `Enter` or `Cmd` + `Shift` +`Enter`	Unmark translation as Needing edit and submit it.
`Alt` + `Enter` or `Option` + `Enter`	Submit the string as a suggestion; this works the same as pressing Suggest while editing translation.
`Ctrl` + `E` or `Cmd` + `E`	Focus on translation editor.
`Ctrl` + `U` or `Cmd` + `U`	Focus on comment editor.
`Ctrl` + `M` or `Cmd` + `M`	Shows Automatic suggestions tab.
`Ctrl` + `1` to `Ctrl` + `9` or `Cmd` + `1` to `Cmd` + `9`	Copies placeable of a given number from source string.
`Ctrl` + `M` followed by `1` to `9` or `Cmd` + `M` followed by `1` to `9`	Copy the machine translation of a given number to current translation.
`Ctrl` + `I` followed by `1` to `9` or `Cmd` + `I` followed by `1` to `9`	Ignore one item in the list of failing checks.
`Ctrl` + `J` or `Cmd` + `J`	Shows the Nearby strings tab.
`Ctrl` + `S` or `Cmd` + `S`	Focus on search field.
`Ctrl` + `O` or `Cmd` + `O`	Copy the source string.
`Ctrl` + `Y` or `Cmd` + `Y`	Toggle the Needs editing checkbox.
`→`	Browse the next translation string.
`←`	Browse the previous translation string.