Warning
This is an unpolished draft of the second edition of this ebook. If you find any error or have suggestions to improve the text, please create an issue via https://github.com/obonaventure/cnp3/issues?milestone=2
| task_id: | mcqipv6bis |
|---|
The IPv6 packet header includes several fields that are shown in the figure below.
.. question:: ipv6packet
:nb_prop: 3
:nb_pos: 1
Among the following affirmations about the role of these different fields, only one is *incorrect*. Select the incorrect affirmation.
.. positive:: A router never changes any field of an IPv6 packet that it forwards.
.. comment:: This affirmation is incorrect. A router changes the Hop-Limit of the packets that it forwards. It may also change other fields such as the TClass, but this is outside the scope of this ebook.
.. positive:: When a host sends an IPv6 packet, its HopLimit is always set to zero. Routers increment the value of this field for each packet that they forward.
.. comment:: This affirmation is incorrect. A host sends packets with a positive HopLimit and routers decrement this field.
.. negative:: A router always decrements the HopLimit of all forwarded IPv6 packets.
.. comment:: This affirmation is correct.
.. negative:: To forward a packet, a router always looksup the destination address inside its forwarding table.
.. comment:: This affirmation is correct.
.. negative:: The NextHeader field of the IPv6 packet identifies the type of transport segment contained in the packet.
- The IPv6 addresses are 128 bits wide and can be represented by using the hexadecimal representation defined in RFC 5952.
.. question:: ip6addre
:nb_prop: 5
:nb_pos: 3
Among the following textual representations, select all the ones that correspond to a valid IPv6 address.
.. positive:: ``2001:db8:0:0:1::1``
.. positive:: ``2001:db8:a:bb:cc:ddd::1``
.. negative:: ``2001:db8:a:bb:cc:ddd:eeee::1``
.. comment:: This address is invalid. The textual representation of an IPv6 address cannot contain more than 7 individual fields if we two semi columns ``::``
.. negative:: ``2001:db8:a:bb:cc:ddddd::1``
.. comment:: This address is invalid. The textual representation of an IPv6 address cannot contain more than 4 hexadecimal characters between two semi columns ``:``
.. negative:: ``2001:db8:a:bb::cc:ddd::1``
..comment:: This address is invalid. An IPv6 address cannot contain twice two consecutive semicolumns ``::``
.. positive:: ``2001:db8:1234:1234:1234:5678::1``
.. positive:: ``2001:db8:1234::1234:5678:abc:1``
.. positive:: ``2001:db8:1234:5678::abc:1``
.. negative:: ``2001:dg8:1234:abcd::cafe``
.. comment:: This address is invalid. An IPv6 address can only contain digits and letters ``a-f``.
.. negative:: ``2001:dead:beef:bad:cafe:1234:abcd:cafe:1``
.. comment:: This address is invalid. An IPv6 address is 128 bits long. This representation is 144 bits long.
.. question:: ipv6addrb
:nb_prop: 4
:nb_pos: 2
3. Among the textual representation for IPv6 addresses below, select all the ones that correspond to IPv6 address ``2001:db8:0:0:a::cafe``.
.. positive:: ``2001:db8:0:0:a:0:0:cafe``
.. positive:: ``2001:db8:0:0:a::cafe``
.. positive:: ``2001:0db8:0:0:a::cafe``
.. positive:: ``2001:0db8:0000:0000:000a::cafe``
.. positive:: ``2001:0db8::a:0:0:cafe``
.. negative:: ``2001:0db8::a::cafe``
.. comment:: This IPv6 address is ambiguous. An IPv6 address cannot contain twice two successive semi-columns ``::``.
.. negative:: ``2001:db8:0:0:a000::cafe``
.. comment:: This IPv6 address does not correspond to ``2001:db8:0:0:a::cafe``. In this address, the ``a`` 16 bits block corresponds to the following binary representation ``0000 0000 0000 1010`` while the binary representation for ``a000`` is ``1010 0000 0000 0000``.
.. negative:: ``2001:db80:0:0:a::cafe``
.. comment:: This IPv6 address does not correspond to ``2001:db8:0:0:a::cafe``. In this address, the ``db8`` 16 bits block corresponds to the following binary representation ``0000 1101 1011 1000`` while the binary representation for ``db80`` is ``1101 1011 1000 0000``.
- The forwarding tables used in an IPv6 network define the forwarding paths that are used for the packets. Consider the simple network depicted in the figure below. In this network, the hosts have the following addresses :
- host
A:2001:db8:1341:1::Aand its default route points to2001:db8:1341:1::1- host
B:2001:db8:1341:3::Band its default route points to2001:db8:1341:3::3
The routers have one address inside each network :
- router
R1uses address2001:db8:1341:1::1on its West interface, address2001:db8:1341:12::1on its East interface and address2001:db8:1341:13::1on its South interface- router
R2uses address2001:db8:1341:12::2on its West interface and address2001:db8:1341:23::2on its South-West interface- router
R3uses address2001:db8:1341:3::3on its East interface, address2001:db8:1341:23::3on its North-East interface and address2001:db8:1341:13::3on its North interface
The forwarding tables of these three routers, ignoring the routes to the local interfaces, are shown in the figure below.
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[ftable, above=of R1] (FR1) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:3/64 & 2001:db8:1341:12::2 \\
2001:db8:1341:23/64 & 2001:db8:1341:13::3 \\
\end{tabular}};
\node[router,right=of R1] (R2) {R2};
\node[ftable, right=of R2] (FR2) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:3/64 & 2001:db8:1341:23::3 \\
2001:db8:1341:1/64 & 2001:db8:1341:12::1 \\
2001:db8:1341:13/64 & 2001:db8:1341:23::3 \\
\end{tabular}\\};
\node[router,below=of R1] (R3) {R3};
\node[ftable, below=of R3] (FR3) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:1/64 & 2001:db8:1341:13::1 \\
2001:db8:1341:12/64 & 2001:db8:1341:23::2 \\
\end{tabular}\\};
\node[host, right=of R3] (B) {B};
\path[draw,thick]
(A) edge (R1)
(R1) edge (R2)
(R2) edge (R3)
(R1) edge (R3)
(R3) edge (B);
\draw[arrow, dashed] (FR1) -- (R1);
\draw[arrow, dashed] (FR2) -- (R2);
\draw[arrow, dashed] (FR3) -- (R3);
.. question:: ip6path1
:nb_prop: 3
:nb_pos: 2
In the list below, select all the graphs below that represent the correct path followed by packets from ``A`` to ``B`` or from ``B`` to ``A``.
.. positive::
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[host, right=of R3] (B) {B};
\draw[arrow, color=red] (A) -- (R1);
\draw[arrow, color=red] (R1) -- (R2);
\draw[arrow, color=red] (R2) -- (R3);
\draw[arrow, color=red] (R3) -- (B);
.. negative::
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[host, right=of R3] (B) {B};
\draw[arrow, color=red] (B) -- (R3);
\draw[arrow, color=red] (R3) -- (R2);
\draw[arrow, color=red] (R2) -- (R1);
\draw[arrow, color=red] (R1) -- (A);
.. comment:: Check the nethop for the route towards ``2001:db8:1341:1/64`` on router ``R3``
.. negative::
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[host, right=of R3] (B) {B};
\draw[arrow, color=red] (A) -- (R1);
\draw[arrow, color=red] (R1) -- (R3);
\draw[arrow, color=red] (R3) -- (B);
.. comment:: Check the nethop for the route towards ``2001:db8:1341:3/64`` on router ``R1``
.. positive::
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[host, right=of R3] (B) {B};
\draw[arrow, color=red] (B) -- (R3);
\draw[arrow, color=red] (R3) -- (R1);
\draw[arrow, color=red] (R1) -- (A);
- Consider the network shown in the figure below. In this network, the following addresses are used.
- host
A:2001:db8:1341:1::Aand its default route points to2001:db8:1341:1::1- host
B:2001:db8:1341:4::Band its default route points to2001:db8:1341:4::4
The routers have one address inside each network :
- router
R1uses address2001:db8:1341:1::1on its West interface, address2001:db8:1341:12::1on its East interface and address2001:db8:1341:13::1on its South interface- router
R2uses address2001:db8:1341:12::2on its West interface, address2001:db8:1341:23::2on its South-West interface and address2001:db8:1341:24::2on its South interface.- router
R3uses address2001:db8:1341:34::3on its East interface, address2001:db8:1341:23::3on its North-East interface and address2001:db8:1341:13::3on its North interface- router
R4uses address2001:db8:1341:34::4on its West interface, address2001:db8:1341:24::4on its North interface and address2001:db8:1341:4::4on its East interface
The forwarding paths used in a network depend on the forwarding tables installed in the network nodes. Sometimes, these forwarding tables must be configured manually.
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[ftable, above=of R1] (FR1) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:4/64 & 2001:db8:1341:12::2 \\
2001:db8:1341:23/64 & 2001:db8:1341:13::3 \\
2001:db8:1341:34/64 & 2001:db8:1341:13::3 \\
2001:db8:1341:24/64 & 2001:db8:1341:12::2 \\
\end{tabular}};
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[router,below=of R2] (R4) {R4};
\node[ftable,below=of R4] (FR4) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:1/64 & 2001:db8:1341:34::3 \\
2001:db8:1341:23/64 & 2001:db8:1341:24::2 \\
2001:db8:1341:13/64 & 2001:db8:1341:34::3 \\
2001:db8:1341:12/64 & 2001:db8:1341:24::2 \\
\end{tabular}\\};
\node[host, right=of R4] (B) {B};
\path[draw,thick]
(A) edge (R1)
(R1) edge (R2)
(R2) edge (R3)
(R1) edge (R3)
(R4) edge (R3)
(R2) edge (R4)
(R4) edge (B);
\draw[arrow, dashed] (FR1) -- (R1);
\draw[arrow, dashed] (FR4) -- (R4);
.. question:: 4routers
:nb_prop: 4
:nb_pos: 2
In this network, select `all` the forwarding tables below that ensure that hosts ``A`` and ``B`` can exchange packets in both directions.
.. positive:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:23::2
2001:db8:1341:4/64 2001:db8:1341:34::4
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:12::1
2001:db8:1341:4/64 2001:db8:1341:24::4
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. positive:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:13::1
2001:db8:1341:4/64 2001:db8:1341:34::4
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:12::1
2001:db8:1341:4/64 2001:db8:1341:24::4
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. positive:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:13::1
2001:db8:1341:4/64 2001:db8:1341:34::4
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:12::1
2001:db8:1341:4/64 2001:db8:1341:23::3
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. negative:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:34::4
2001:db8:1341:4/64 2001:db8:1341:34::4
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:12::1
2001:db8:1341:4/64 2001:db8:1341:24::4
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. comment:: The forwarding table of ``R3`` is incorrect, check the nexthop to reach ``2001:db8:1341:4/64``.
.. negative:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:23::2
2001:db8:1341:4/64 2001:db8:1341:34::4
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:23::3
2001:db8:1341:4/64 2001:db8:1341:24::4
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. comment:: These forwarding tables are incorrect. Check what happens when ``R2`` receives a packet towards ``2001:db8:1341::1/64``
.. negative:: New forwarding table for ``R3``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:13::1
2001:db8:1341:4/64 2001:db8:1341:23::2
2001:db8:1341:12/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:23::2
==================== ===================
New forwarding table for ``R2``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:12::1
2001:db8:1341:4/64 2001:db8:1341:23::3
2001:db8:1341:13/64 2001:db8:1341:12::1
2001:db8:1341:34/64 2001:db8:1341:23::3
==================== ===================
.. comment:: These forwarding tables are incorrect. Check what happens when ``R2`` receives a packet towards ``2001:db8:1341::4/64``
Consider the same network as in the previous question, but now the forwarding tables of
R2andR3are configured as shown below :.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A) {A}; \node[router, right=of A] (R1) { R1 }; \node[router,right=of R1] (R2) {R2}; \node[ftable, above=of R2] (FR2) { \begin{tabular}{l|l} Dest. & Nexthop \\ \hline 2001:db8:1341:1/64 & 2001:db8:1341:12::1 \\ 2001:db8:1341:4/64 & 2001:db8:1341:23::3 \\ 2001:db8:1341:13/64 & 2001:db8:1341:23::3 \\ 2001:db8:1341:34/64 & 2001:db8:1341:23::3 \\ \end{tabular}}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[ftable,below=of R3] (FR3) { \begin{tabular}{l|l} Dest. & Nexthop \\ \hline 2001:db8:1341:1/64 & 2001:db8:1341:23::2 \\ 2001:db8:1341:4/64 & 2001:db8:1341:34::4 \\ 2001:db8:1341:12/64 & 2001:db8:1341:23::2 \\ 2001:db8:1341:24/64 & 2001:db8:1341:23::2 \\ \end{tabular}\\}; \node[host, right=of R4] (B) {B}; \path[draw,thick] (A) edge (R1) (R1) edge (R2) (R2) edge (R3) (R1) edge (R3) (R4) edge (R3) (R2) edge (R4) (R4) edge (B); \draw[arrow, dashed] (FR2) -- (R2); \draw[arrow, dashed] (FR3) -- (R3);
.. question:: 4routersb
:nb_prop: 3
:nb_pos: 1
In this network, select `all` the forwarding tables below that ensure that the packets sent from ``A`` to ``B`` follow the reverse path of the packets sent by ``B`` to ``A``.
.. positive:: New forwarding table for ``R1``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:4/64 2001:db8:1341:12::2
2001:db8:1341:23/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:12::2
2001:db8:1341:34/64 2001:db8:1341:13::3
==================== ===================
New forwarding table for ``R4``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:34::4
2001:db8:1341:13/64 2001:db8:1341:34::3
2001:db8:1341:12/64 2001:db8:1341:24::2
2001:db8:1341:23/64 2001:db8:1341:24::2
==================== ===================
.. negative:: New forwarding table for ``R1``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:4/64 2001:db8:1341:13::3
2001:db8:1341:23/64 2001:db8:1341:12::2
2001:db8:1341:24/64 2001:db8:1341:12::2
2001:db8:1341:34/64 2001:db8:1341:13::3
==================== ===================
New forwarding table for ``R4``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:24::2
2001:db8:1341:13/64 2001:db8:1341:34::3
2001:db8:1341:12/64 2001:db8:1341:24::2
2001:db8:1341:23/64 2001:db8:1341:24::2
==================== ===================
.. comment:: The two paths ``A->B`` and ``B->A`` do not pass through the same routers.
.. negative:: New forwarding table for ``R1``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:4/64 2001:db8:1341:12::2
2001:db8:1341:23/64 2001:db8:1341:13::3
2001:db8:1341:24/64 2001:db8:1341:12::2
2001:db8:1341:34/64 2001:db8:1341:13::3
==================== ===================
New forwarding table for ``R4``:
==================== ===================
Dest. Nexthop
==================== ===================
2001:db8:1341:1/64 2001:db8:1341:24::2
2001:db8:1341:13/64 2001:db8:1341:34::3
2001:db8:1341:12/64 2001:db8:1341:24::2
2001:db8:1341:23/64 2001:db8:1341:24::2
==================== ===================
.. comment:: The two paths ``A->B`` and ``B->A`` do not pass through the same routers.
- Consider again the same network with three routers as discussed earlier. Let us know explore how :manpage:`traceroute6(8)` operates in such a network. A key point to remember about :manpage:`traceroute6(8)` is that when it returns an ICMP message, this message is sent inside a packet whose source is one of the addresses of the router and whose destination is the source address of the packet that triggered the generation of this ICMP message. In this network, the hosts have the following addresses :
- host
A:2001:db8:1341:1::Aand its default route points to2001:db8:1341:1::1- host
B:2001:db8:1341:3::Band its default route points to2001:db8:1341:3::3
The routers have one address inside each network :
- router
R1uses address2001:db8:1341:1::1on its West interface, address2001:db8:1341:12::1on its East interface and address2001:db8:1341:13::1on its South interface- router
R2uses address2001:db8:1341:12::2on its West interface and address2001:db8:1341:23::2on its South-West interface- router
R3uses address2001:db8:1341:3::3on its East interface, address2001:db8:1341:23::3on its North-East interface and address2001:db8:1341:13::3on its North interface
The forwarding tables of these three routers, ignoring the routes to the local interfaces, are shown in the figure below.
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[ftable, above=of R1] (FR1) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:3/64 & 2001:db8:1341:12::2 \\
2001:db8:1341:23/64 & 2001:db8:1341:13::3 \\
\end{tabular}};
\node[router,right=of R1] (R2) {R2};
\node[ftable, right=of R2] (FR2) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:3/64 & 2001:db8:1341:23::3 \\
2001:db8:1341:1/64 & 2001:db8:1341:12::1 \\
2001:db8:1341:13/64 & 2001:db8:1341:23::3 \\
\end{tabular}\\};
\node[router,below=of R1] (R3) {R3};
\node[ftable, below=of R3] (FR3) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
2001:db8:1341:1/64 & 2001:db8:1341:13::1 \\
2001:db8:1341:12/64 & 2001:db8:1341:23::2 \\
\end{tabular}\\};
\node[host, right=of R3] (B) {B};
\path[draw,thick]
(A) edge (R1)
(R1) edge (R2)
(R2) edge (R3)
(R1) edge (R3)
(R3) edge (B);
\draw[arrow, dashed] (FR1) -- (R1);
\draw[arrow, dashed] (FR2) -- (R2);
\draw[arrow, dashed] (FR3) -- (R3);
.. question:: traceroute6
:nb_prop: 3
:nb_pos: 2
In this network, select the all traceroute outputs that are correct according to the forwarding tables shown above.
.. positive::
.. code-block:: console
traceroute6 to 2001:db8:1341:1::A from 2001:db8:1341:3::B
1 2001:db8:1341:3::3
2 2001:db8:1341:13::1
3 2001:db8:1341:1::A
.. comment:: This traceroute is correct but note that it's likely possible that the penultimate address will be an other IPv6 address of `R1`: ``2001:db8:1341:12::1`` instead of ``2001:db8:1341:13::1``, it depends if the ICMP package takes the path to the previous router or to the source (the reversed path is different according to the forwarding tables).
.. negative::
.. code-block:: console
traceroute6 to 2001:db8:1341:1::A from 2001:db8:1341:3::B
1 2001:db8:1341:3::3
2 2001:db8:1341:23::2
3 2001:db8:1341:12::1
4 2001:db8:1341:1::A
.. comment:: This traceroute is incorrect. Check the forwarding table of ``R3`` towards ``2001:db8:1341:1/64``
.. negative::
.. code-block:: console
traceroute6 to 2001:db8:1341:3::B from 2001:db8:1341:1::A
1 2001:db8:1341:1::1
2 2001:db8:1341:13::3
3 2001:db8:1341:3::B
.. comment:: This traceroute is incorrect. Check the forwarding table of ``R1`` towards ``2001:db8:1341:3/64``
.. positive::
.. code-block:: console
traceroute6 to 2001:db8:1341:3::B from 2001:db8:1341:1::A
1 2001:db8:1341:1::1
2 2001:db8:1341:12::2
3 2001:db8:1341:23::3
4 2001:db8:1341:3::B
.. comment:: This traceroute is correct but note that it's likely possible that the penultimate address will be an other IPv6 address of `R3`: ``2001:db8:1341:13::3`` instead of ``2001:db8:1341:23::3``, it depends if the ICMP package takes the path to the previous router or to the source (the reversed path is different according to the forwarding tables).
- When manipulating IPv6 address, it is sometimes necessary to convert an IPv6 address in its binary representation.
.. question:: ipv6addr
:nb_prop: 3
:nb_pos: 1
Among the following binary representations, which is the one that corresponds to address ``2001:DB8:1341:FC81::1`` (the first line shows the higher order 64 bits starting from the highest order bits, the second the low order 64 bits) ?
.. positive::
.. code-block:: console
00100000 00000001 00001101 10111000 00010011 01000001 11111100 10000001
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001
.. negative::
.. code-block:: console
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001
00100000 00000001 00001101 10111000 00010011 01000001 11111100 10000001
.. comment:: This is the binary representation for IPv6 address ``0000:0000:0000:0001:2001:DB8:1341:FC81``
.. negative::
.. code-block:: console
00000001 00100000 10111000 00001101 010000000010011 1 10000001 11111100
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001
.. comment:: This is the binary representation for IPv6 address ``0120:80DB:4113:81FC::1``
.. negative::
.. code-block:: console
00100000 00000001 11011011 10000000 00010011 01000001 11111100 10000001
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000001
.. comment:: This is the binary representation for IPv6 address ``2001:DB80:1341:FC81::1``
- When an IPv6 router receives a packet to be forwarded, it finds the most specific match for the destination address of this packet in its forwarding table. Consider the following forwarding table from an hypothetical IPv6 router.
2001:DB8:1341::/48, via nexthop1 2001:DB8:1341:2000/51, via nexthop5 2001:DB8:1341:2000/64, interface1 2001:DB8:1341:4000/50, via nexthop2 2001:DB8:1341:5000/52, nexthop3 2001:DB8:1341:7000/64, interface2 2001:DB8:1341:5555/64, interface3 2001:DB8::/16 via nexthop4 ::/0 via nexthop0
.. question:: ipv6morespecific
:nb_prop: 5
:nb_pos: 3
Among the following affirmations about the matching of destination addresses in the forwarding tables, select all the *correct* ones.
.. positive:: A packet whose destination address is ``2001:DB8:1342:5555::1`` will be forwarded via ``nexthop4``
.. comment:: This destination address matches ``2001:DB8::/16``
.. negative:: A packet whose destination address is ``2001:DB8:1342:5555::1`` will be forwarded via ``interface3``
.. comment:: No, this destination address matches route ``2001:DB8::/16``
.. positive:: A packet whose destination address is ``2001:DB8:1341:3000::1`` will be forwarded via ``nexthop5``
.. comment:: This destination address matches ``2001:DB8:1341:2000/51``
.. negative:: A packet whose destination address is ``2001:DB8:1341:3000::1`` will be forwarded via ``nexthop0``
.. comment:: No, this destination address matches route ``2001:DB8:1341:2000/51``
.. negative:: A packet whose destination address is ``2001:DB8:1341:3000::1`` will be forwarded via ``nexthop1``
.. comment:: No, this destination address matches route ``2001:DB8:1341:2000/51``
.. positive:: A packet whose destination address is ``2001:DB8:1341:6000::1`` will be forwarded via ``nexthop2``
.. comment:: This destination address matches ``2001:DB8:1341:4000/50``
.. negative:: A packet whose destination address is ``2001:DB8:1341:6000::1`` will be forwarded via ``nexthop0``
.. comment:: No, this destination address matches route ``2001:DB8:1341:4000/50``
.. negative:: A packet whose destination address is ``2001:DB8:1341:6000::1`` will be forwarded via ``nexthop1``
.. comment:: No, this destination address matches route ``2001:DB8:1341:4000/50``
.. positive:: A packet whose destination address is ``2001:DB8:1341:5000::1`` will be forwarded via ``nexthop3``
.. comment:: This destination address matches ``2001:DB8:1341:5000/52``
.. negative:: A packet whose destination address is ``2001:DB8:1341:5000::1`` will be forwarded via ``nexthop2``
.. comment:: No, this destination address matches route ``2001:DB8:1341:5000/52``
.. negative:: A packet whose destination address is ``2001:DB8:1341:5000::1`` will be forwarded via ``nexthop1``
.. comment:: No, this destination address matches route ``2001:DB8:1341:5000/52``
- Consider the network shown in the figure below. In this network, the following addresses are used.
- host
A:2001:db8:1341:1::Aand its default route points to2001:db8:1341:1::1- host
B:2001:db8:1341:4::Band its default route points to2001:db8:1341:4::4
The routers have one address inside each network :
- router
R1uses address2001:db8:1341:1::1on its West interface, address2001:db8:1341:12::1on its East interface and address2001:db8:1341:13::1on its South interface- router
R2uses address2001:db8:1341:12::2on its West interface, and address2001:db8:1341:24::2on its South interface- router
R3uses address2001:db8:1341:34::3on its East interface and address2001:db8:1341:13::3on its North interface- router
R4uses address2001:db8:1341:34::4on its West interface, address2001:db8:1341:24::4on its North interface and address2001:db8:1341:4::4on its East interface
Routers R2 and R3 are buggy in this network. Besides the routes for their local interfaces (not shown in the figure), they only have a default route which is shown in the figure below.
.. tikz::
:libs: positioning, matrix, arrows
\tikzstyle{arrow} = [thick,->,>=stealth]
\tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, }
\tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, }
\tikzset{ftable/.style={rectangle, dashed, draw} }
\node[host] (A) {A};
\node[router, right=of A] (R1) { R1 };
\node[ftable, above=of R1] (FR2) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
::/0 & 2001:db8:1341:12::1 \\
\end{tabular}};
\node[router,right=of R1] (R2) {R2};
\node[router,below=of R1] (R3) {R3};
\node[router,below=of R2] (R4) {R4};
\node[ftable,below=of R4] (FR3) { \begin{tabular}{l|l}
Dest. & Nexthop \\
\hline
::/0 & 2001:db8:1341:34::4 \\
\end{tabular}\\};
\node[host, right=of R4] (B) {B};
\path[draw,thick]
(A) edge (R1)
(R1) edge (R2)
(R1) edge (R3)
(R4) edge (R3)
(R2) edge (R4)
(R4) edge (B);
\draw[arrow, dashed] (FR2) -- (R2);
\draw[arrow, dashed] (FR3) -- (R3);
How do you configure the forwarding tables on R1 and R4 so that A can reach B and the reverse ?
Consider a slightly different network than in the previous question.
.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A) {A}; \node[router, right=of A] (R1) { R1 }; \node[router,right=of R1] (R2) {R2}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[host, right=of R4] (B) {B}; \path[draw,thick] (A) edge (R1) (R1) edge (R2) (R1) edge (R3) (R1) edge (R4) (R4) edge (R3) (R2) edge (R4) (R4) edge (B);
Assuming that the following IPv6 addresses are used :
- host
A:2001:db8:1341:1::Aand its default route points to2001:db8:1341:1::1- host
B:2001:db8:1341:4::Band its default route points to2001:db8:1341:4::4
The routers have one address inside each network :
- router
R1uses address2001:db8:1341:1::1on its West interface, address2001:db8:1341:12::1on its East interface, address2001:db8:1341:14::1on its South-East interface and address2001:db8:1341:13::1on its South interface- router
R2uses address2001:db8:1341:12::2on its West interface, and address2001:db8:1341:24::2on its South interface- router
R3uses address2001:db8:1341:34::3on its East interface and address2001:db8:1341:13::3on its North interface- router
R4uses address2001:db8:1341:34::4on its West interface, address2001:db8:1341:24::4on its North interface, address2001:db8:1341:14::4on its North-West interface and address2001:db8:1341:4::4on its East interfaceCan you configure the forwarding tables so that the following paths are used by packets sent by host
Ato reach one of the four addresses of routerR4?.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A) {A}; \node[router, right=of A] (R1) { R1 }; \node[router,right=of R1] (R2) {R2}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[host, right=of R4] (B) {B}; \path[draw,arrow, color=red, thick] (A) edge (R1) (R1) edge (R2) (R2) edge (R4);.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A) {A}; \node[router, right=of A] (R1) { R1 }; \node[router,right=of R1] (R2) {R2}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[host, right=of R4] (B) {B}; \path[draw,arrow, color=blue, thick] (A) edge (R1) (R1) edge (R4);.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A) {A}; \node[router, right=of A] (R1) { R1 }; \node[router,right=of R1] (R2) {R2}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[host, right=of R4] (B) {B}; \path[draw,arrow, color=green, thick] (A) edge (R1) (R1) edge (R3) (R3) edge (R4);Do your forwarding tables impose the path used to reach host
Bwhich is attached to routerR4or do you need to configure an additional entry in these tables ?
- Consider the network below that contains only routers. This network has been configured by a group of students and you must verify whether the configuration is correct. All the IPv6 addresses are part of the same
/48prefix that we namep. The following subnets are defined in this/48prefix.
p:12/64for the link betweenR1andR2. On this subnet,R1uses addressp:12::1while routerR2uses addressp:12::2
p:13/64for the link betweenR1andR3. On this subnet,R1uses addressp:13::1while routerR3uses addressp:13::3
p:24/64for the link betweenR2andR4. On this subnet,R2uses addressp:24::2while routerR4uses addressp:24::4...
.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[router] (R1) {R1}; \node[router,right=of R1] (R2) {R2}; \node[router,right=of R2] (R5) {R5}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[router,below=of R5] (R6) {R6}; \path[draw,thick] (R1) edge (R2) (R1) edge (R3) (R4) edge (R3) (R2) edge (R4) (R2) edge (R5) (R4) edge (R6) (R5) edge (R6);
The students have configured the following forwarding tables on these six routers.
on router
R1.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR1) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline ::/0 & p:12::2 \\ p:12::/64 & East \\ p:13::/64 & South\\ p:25::/64 & p:12::2\\ p:34::/64 & p:12::2\\ \end{tabular}};on router
R2.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR2) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline ::/0 & p:12::1 \\ p:12::/64 & West \\ p:13::/64 & p:24::4\\ p:24::/64 & South\\ p:25::/64 & East\\ p:56::/64 & p:24::4\\ \end{tabular}};on router
R3.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR3) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline ::/0 & p:13::1\\ p:13::/64 & North \\ p:34::/64 & East\\ p:56::/64 & p:34::4\\ \end{tabular}};on router
R5.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR5) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline ::/0 & p:56::6 \\ p:12::/64 & p:25::2\\ p:25::/64 & West \\ p:56::/64 & South\\ \end{tabular}};on router
R4.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR4) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline p:12::/63 & p:24::2\\ p:24::/64 & North\\ p:25::/64 & p:46::6\\ p:34::/64 & West\\ p:46::/64 & East\\ \end{tabular}};on router
R6.. tikz:: :libs: positioning, matrix, arrows \tikzset{ftable/.style={rectangle, dashed, draw} } \node[ftable] (FR6) { \begin{tabular}{l|l} Dest. & Nexthop/Interface \\ \hline ::/0 & p:56::5 \\ p:13::/64 & p:46::4\\ p:24::/63 & p:46::4\\ p:34::/64 & p:46::4\\ p:46::/64 & West\\ p:56::/64 & North\\ \end{tabular}};
Sometimes, static routes must be configured on networks to enforce certain paths. Consider the six routers network shown in the figure below.
.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A1) {A1}; \node[router, right=of A1] (R1) {R1}; \node[host, below=of A1] (A2) {A2}; \node[router,right=of R1] (R2) {R2}; \node[router,right=of R2] (R5) {R5}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R2] (R4) {R4}; \node[router,below=of R5] (R6) {R6}; \node[host, right=of R5] (B1) {B1}; \node[host, right=of R6] (B2) {B2}; \path[draw,thick] (A1) edge (R1) (A2) edge (R3) (R1) edge (R2) (R1) edge (R3) (R4) edge (R3) (R2) edge (R4) (R2) edge (R5) (R4) edge (R6) (R5) edge (R6) (R5) edge (B1) (R6) edge (B2);In this network, we will focus on four IPv6 prefixes :
p:0000::/64used on the linkA1-R1.A1uses addressp:0000::A1/64p:0001::/64used on the linkA2-R3.A2uses addressp:0001::A2/64p:0002::/64used on the linkB1-R5.B1uses addressp:0002::B1/64p:0003::/64used on the linkB2-R6.B2uses addressp:0003::B2/64
Can you configure the forwarding tables of the six routers to achieve the following network objectives :
- All packets sent by
B1andB2toA1andA2are always forwarded viaR2while all packets fromA1andA2are always forwarded viaR4 - The packets whose destinations are
A1,A2,B1orB2are never forwarded via routerR4 - The packets sent by
A1orA2towardsB1are always forwarded viaR2while the packets towardsB2are always forwarded viaR4.
When creating these forwarding tables, try to minimise the number of entries that you install on each router.
When a network is designed, an important element of the design is the IP address allocation plan. A good allocation plan can provide flexibility and help to reduce the size of the forwarding tables.
.. tikz:: :libs: positioning, matrix, arrows \tikzstyle{arrow} = [thick,->,>=stealth] \tikzset{router/.style = {rectangle, draw, text centered, minimum height=2em}, } \tikzset{host/.style = {circle, draw, text centered, minimum height=2em}, } \tikzset{ftable/.style={rectangle, dashed, draw} } \node[host] (A1) {A1}; \node[router, right=of A1] (R1) {R1}; \node[host, below=of A1] (A2) {A2}; \node[router,right=of R1] (R2) {R2}; \node[router,right=of R2] (R5) {R5}; \node[router,below=of R1] (R3) {R3}; \node[router,below=of R5] (R6) {R6}; \node[host, right=of R5] (B1) {B1}; \node[host, right=of R6] (B2) {B2}; \path[draw,thick] (A1) edge (R1) (A2) edge (R3) (R1) edge (R3) (R2) edge (R3) (R2) edge (R5) (R2) edge (R6) (R5) edge (R6) (R5) edge (B1) (R6) edge (B2);
Assign IP subnets to all links in this network so that you can reduce the number of entries in the forwarding tables of all routers. Assume that you have received a/56prefix that you can use as you want. Each subnet containing a host must be allocated a/64subnet.