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<!doctype html>
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<head>
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<title>Advanced Networking - Module 1 Chapter 6 - Network Layer</title>
<meta name="description" content="Abilitante alle certificazioni Cisco CCENT e CCNA">
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<div class="reveal">
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<div class="slides">
<section>
<h1>Advanced Networking</h1>
<h2>Routing & Switching:</h2>
<h2>Introduction to Networks</h2>
<h3>Chapter 6: Network Layer</h3>
<small><a href="http://hlcs.it">Hacklab Cosenza</a> / Centro di Ricerca su Tecnologia e Innovazione</small>
</section>
<section>
<h2>The OSI L3: Network</h2>
<p>The network layer provides the means for <strong>end-to-end connectivity</strong> networks. It carries 4 basic operations:</p>
<ul>
<li><strong>Addressing</strong> for the sender and receiver end of the network communication.</li>
<li><strong>Encapsulation</strong> of the transport layer (L4) Protocol Data Unit (PDU) in a <em>packet</em>.</li>
<li><strong>Routing</strong> packets through networks, selecting paths and <em>hops</em>.</li>
<li><strong>De-encapsulation</strong> of the packet into a L4 PDU at the receiver end.</li>
</ul>
<p><u>L2 is for link-to-link, L3 is for end-to-end</u>.</p>
</section>
<section>
<h2>The IP Protocol</h2>
<p>IP was designed as a protocol with <strong>low overhead</strong>. It <strong>doesn't track nor manage the flow of packets</strong> (delegates to upper layers). Its basic characteristics are:</p>
<ul>
<li><strong>Connectionless</strong>: no connection with the destination is established before sending data packets. Like with a paper letter, the recipient might be absent, not receiving, unable to read.</li>
<li><strong>Best Effort (unreliable)</strong>: There is no acknowledgment or error control. Packet delivery and ordering are not guaranteed.</li>
<li><strong>Media Independent</strong>: Operation is independent of the medium carrying the data, except for the <strong>MTU (Maximum Transmission Unit)</strong> which L3 must coordinate with L2.</li>
</ul>
</section>
<section>
<section>
<h2>IPv4 Packet</h2>
<img src="http://i.imgur.com/8narbYh.jpg">
<p><small><strong>Options</strong> and <strong>Padding</strong> are almost never used.</small></p>
</section>
<section>
<h2>IPv4 Packet Fields</h2>
<p>An IPv4 packet has two sections:</p>
<ul>
<li><strong>IP Header</strong> - Identifies the packet characteristics.</li>
<li><strong>Payload</strong> - contains the encapsulated L4 segment, with the actual data.</li>
</ul>
</section>
<section>
<h2>IPv4 Packet Header</h2>
<ul>
<li><strong>Version</strong> - 4 bit value identifying the IP protocol version. It's 0100 for IPv4 packets.</li>
<li><strong>Type of Service (ToS)</strong> - Now called <strong>Differentiated Services (DS)</strong>, it helps in determining the priority of each packet.</li>
<li><strong>Time-to-Live (TTL)</strong> - 8-bit counter used to specify the lifetime of a packet. It's set by the sender in terms of <strong>hop count</strong>.</li>
<li><strong>Protocol</strong>: 8-bit value expressing which encapsulated protocol the payload consists of. Common values are 0x01 for ICMP, 0x06 for TCP, 0x17 fot UDP.</li>
</ul>
</section>
<section>
<h2>IPv4 Packet Fields</h2>
<ul>
<li><strong>Internet Header Length (IHL)</strong> - The number of 32-bit words in the header (5-15).</li>
<li><strong>Total Length</strong> - Defines the entire packet (fragment) size in bytes, including header and data. <u>Minimum</u> is 20 bytes (20-byte header + 0 byte data), <u>maximum</u> is 65535 bytes.</li>
<li><strong>Header Checksum</strong> - 16-bit used for error control.</li>
</ul>
</section>
<section>
<h2>IPv4 Packet Fields</h2>
<p>Used when an IP packet has to be fragmented because transmission on <strong>media with smaller MTUs</strong>:</p>
<ul>
<li><strong>Identification</strong> - 16 bits to uniquely identify fragments.</li>
<li><strong>Flags</strong> - 3 bits identifying how the packet is fragmented.</li>
<li><strong>Fragment Offset</strong> - 13 bits identifying the order of the fragments when reconstructing the unfragmented original.</li>
</ul>
</section>
</section>
<!--
<section>
<h1>Practice IPv4 Packets</h1>
<h1>with WireShark</h1>
</section>
-->
<section>
<section>
<h2>IPv4 Limitations</h2>
<h3>Scarcity of IPv4 Addresses</h3>
<p>The IPv4 addressing uses a <strong>32-bit address space</strong> for a total 4924967296 addresses (3.7 billions really allocatable). <strong>They are not enough</strong> for IoT, always-on connections.</p>
</section>
<section>
<h2>IPv4 Limitations</h2>
<h3>NAT (Network Address Translation)</h3>
<p>Slows down IPv4 addresses depletion, providing <strong>a way to share a single public IP address</strong>. The internal IP address is hidden, and that's problematic for end-to-end connectivity.</p>
</section>
<section>
<h2>IPv4 Limitations</h2>
<h3>Internet Routing Table Expansion</h3>
<p>The growth of the Internet has lead to <strong>an increase of the number of paths router must keep track of</strong>. The way IPv4 works it consumes a lot of memory and computing resources.</p>
</section>
</section>
<section>
<h2>IPv6 Protocol Introduction</h2>
<p>IPv6 was developed to fix IPv4 address exhaustion and deal with present and future needs. How does it <strong>differ from IPv4</strong>?</p>
<ul>
<li><strong>Increased address space</strong>, 128-bit hierarchical addressing.</li>
<li><strong>Simplified but extendable header</strong> with fewer fields (8 fields in 40 bytes instead of IPv4's 12-in-20).</li>
<li><strong>No required</strong> fragmentation and header checksum.</li>
<li><strong>Address autoconfiguration</strong>.</li>
<li><strong>No need for NAT</strong>, every host gets a <strong>public IPv6</strong> address.</li>
<li><strong>More and integrated security</strong> with authentication and privacy extensions; mandatory <strong>IPsec</strong> in the protocol suite.</li>
<li><strong>Improved packet handling</strong> without the need to de-encapsulate the transport layer to identify traffic flows, thanks to a <strong>Flow Label</strong> field.</li>
<li><strong>Larger payload</strong> support for increasing efficiency.</li>
</ul>
</section>
<section>
<section>
<h2>IPv6 Packet Header</h2>
<img src="http://i.imgur.com/hXuxw2p.png">
</section>
<section>
<h2>IPv4 vs IPv6 Packet Headers</h2>
<img src="http://i.imgur.com/I7KQqds.jpg">
</section>
<section>
<h2>IPv6 Packet Header Fields</h2>
<ul>
<li><strong>Version</strong> (4 bits) - always set to 0110 for IPv6 packets.</li>
<li><strong>Traffic Class</strong> (8 bits) - equivalent to IPv4 Differentiated Services (DS) field.</li>
<li><strong>Flow Label</strong> (20 bits) - used to inform intermediary device to maintain the same path so packets are not reordered.</li>
<li><strong>Payload Length</strong> (16 bits) - Size of EH + payload in bytes.</li>
<li><strong>Next Header</strong> (8 bits) - Normally this is equivalent to IPv4 Protocol field, values are the same.</li>
<ul>
<li>When <strong>extension headers are present</strong> in the packet this field indicates which extension header follows.</li>
</ul>
<li><strong>Hop Limit</strong> (8 bits) - Equivalent to IPv4's Time-to-Live.</li>
<li><strong>Extension Headers (EH)</strong> (Optional) - Placed between the header and the payload.</li>
</ul>
</section>
</section>
<!--
<section>
<h1>Practice IPv6 Packets</h1>
<h1>with WireShark</h1>
</section>
-->
<section>
<h2>Routing for the host</h2>
<p>An host can send (<em>forward</em>) a packet to:</p>
<ul>
<li><strong>Itself</strong> - every host has a special IP address, 127.0.0.1, known as the <strong>loopback interface</strong>, that is useful for testing purposes. IPs in the network 127.0.0.0/8 are loopback IPs.</li>
<li><strong>Local host</strong> - any host on the same network as the sender.</li>
<li><strong>Remote host</strong> - hosts beyond the local network segment.</li>
</ul>
<p><strong>Destination IP address</strong> and <strong>Subnet Mask</strong> combined allow an host to distinguish between local and remote hosts.</p>
<p>A <strong>router</strong> is needed to forward a packet to a remote network.</p>
<p>The (interface of the) router connected to the local network segment and used to reach any other network is called <strong>default gateway</strong>.</p>
</section>
<section>
<h2>Host Routing Table</h2>
<p>An host decides where to forward its traffic based on its routing table, which tipically presents three kinds of entries:</p>
<ul>
<li><strong>Direct Connection(s)</strong>: IP addresses assigned to the host, such as the loopback.</li>
<li><strong>Local Network Route</strong>: the network the host belongs to is <strong>automatically added</strong> to its routing table.</li>
<li><strong>Local Default Route</strong>: the route used to <strong>reach any other network</strong>. It is added, manually or automatically, when a default gateway is present.</li>
</ul>
</section>
<section>
<section>
<h2>IPv4 Host Routing Table</h2>
<h3>Linux</h3>
<pre><code>stefanauss@barney:~$ route -n
Tabella di routing IP del kernel
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.87.23.1 0.0.0.0 UG 0 0 0 eth0
10.87.23.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
stefanauss@barney:~$
stefanauss@barney:~$ ip route show
default via 10.87.23.1 dev eth0 proto static
10.87.23.0/24 dev eth0 proto kernel scope link src 10.87.23.2 metric 1
stefanauss@barney:~$
stefanauss@barney:~$ netstat -r
Tabella di routing IP del kernel
Destination Gateway Genmask Flags MSS Window irtt Iface
default StefanaussGR.la 0.0.0.0 UG 0 0 0 eth0
10.87.23.0 * 255.255.255.0 U 0 0 0 eth0</code></pre>
</section>
<section>
<h2>IPv4 Host Routing Table</h2>
<h3>Windows</h3>
<pre><code>C:\Document and Settings\Stefanauss\>route print
===========================================================================
Elenco interfacce
0x1 ........................... MS TCP Loopback interface
0x2 ...08 00 27 3b 1b 39 ...... Scheda Ethernet PCI AMD PCNET Family
===========================================================================
===========================================================================
Route attive:
Indirizzo rete Mask Gateway Interfac. Metric
0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.15 20
192.168.1.0 255.255.255.0 192.168.1.15 192.168.1.15 20
192.168.1.15 255.255.255.255 127.0.0.1 127.0.0.1 20
192.168.1.255 255.255.255.255 192.168.1.15 192.168.1.15 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
224.0.0.0 240.0.0.0 192.168.1.15 192.168.1.15 20
255.255.255.255 255.255.255.255 192.168.1.15 192.168.1.15 1
Gateway predefinito: 192.168.1.1
===========================================================================
Route permanenti:
Nessuno</code></pre>
</section>
<section>
<h2>IPv6 Host Routing Table</h2>
<pre><code>stefanauss@barney:~$ ifconfig
eth0 Link encap:Ethernet IndirizzoHW e8:11:32:4e:48:6b
indirizzo inet:10.87.23.2 Bcast:10.87.23.255 Maschera:255.255.255.0
indirizzo inet6: fe80::ea11:32ff:fe4e:486b/64 Scope:Link
indirizzo inet6: fd17:8869:6a40::e24/128 Scope:Global [...]
lo Link encap:Loopback locale
indirizzo inet:127.0.0.1 Maschera:255.0.0.0
indirizzo inet6: ::1/128 Scope:Host [...]
stefanauss@barney:~$ ip -6 route show
fd17:8869:6a40::e24 dev eth0 proto kernel metric 256
fe80::/64 dev eth0 proto kernel metric 256</code></pre>
<ul>
<li><strong>::/0</strong> - IPv6 equivalent of 0.0.0.0 default route.</li>
<li><strong>::1/128</strong> - IPv6 loopback address.</li>
<li><strong>fe80::/64</strong> - Local link network route. </li>
<li><strong>ff00::8</strong> - Multicast, equivalent to 224.x.x.x.</li>
<li>IPv6 interfaces have 2 addresses: a <strong>link local</strong> and a <strong>global unicast</strong> address. Also, no broadcast address with IPv6.</li>
</ul>
</section>
</section>
<section>
<h2>Routing for the router</h2>
<p>The routing table of a router contains:</p>
<ul>
<li><strong>Directly-connected routes</strong> - Added when a router interface is configured with an IP address and activated. With these, routers maintain information about the network segments they belong to.</li>
<li><strong>Remote Routes</strong> - Manually added (<em>static routes</em>) or automatically learned (with <em>routing protocols</em>) from other routers connected to other networks.</li>
<li><strong>Default Route</strong> - Similarly to a host, a router can also have a route to a default gateway to be used as a <em>last resort</em>.</li>
</ul>
</section>
<section>
<section>
<h2>Cisco IOS Routing Table</h2>
<p>On a Cisco Router the routing table is obtained with the command <code>show ip route</code>.</p>
<!-- <img src="http://i.imgur.com/UJWLyz3.png" width="50%" height="50%"> -->
<pre><code>R0# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0
D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0
192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks
C 192.168.10.0/24 is directly connected, GigabitEthernet0/0
L 192.168.10.1/32 is directly connected, GigabitEthernet0/0
192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks
C 192.168.11.0/24 is directly connected, GigabitEthernet0/1
L 192.168.11.1/32 is directly connected, GigabitEthernet0/1
209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks
C 209.165.200.224/30 is directly connected, Serial0/0/0
L 209.165.200.225/32 is directly connected, Serial0/0/0
R0#</code></pre>
</section>
<section>
<h2>Cisco IOS Routing Table</h2>
<ul>
<li><strong>Route source</strong> - Identifies how the route was learned.</li>
<li><strong>Destination network</strong> - Identifies the address of the remote network.</li>
<li><strong>Administrative distance</strong> - Identifies the trustworthiness of the route source.</li>
<li><strong>Metric</strong> - Identifies the value assigned to the "difficulty" of reaching the remote network. Lower values indicate preferred routes.</li>
<li><strong>Next-hop</strong> - Identifies the IP address of the next router (gateway to the network) to forward the packet.</li>
<li><strong>Route timestamp</strong> - When the route was last learned.</li>
<li><strong>Outgoing interface</strong> - Identifies the exit interface to use to forward a packet toward the final destination.</li>
</ul>
</section>
</section>
<section>
<h2>Inside a Router</h2>
<img src="http://i.imgur.com/sM72B4N.jpg" width="66%" height="66%">
<p>A router is a proper computer, only with <strong>hardware tailored to perform routing functions</strong>. It has a CPU, an OS, and memories.</p>
</section>
<section>
<h2>Router Memory</h2>
<table>
<tr>
<td><strong>Memory</strong></td>
<td><strong>Type</strong></td>
<td><strong>Content</strong></td>
</tr>
<tr>
<td>RAM</td>
<td>Volatile</td>
<td>Running Cisco IOS; Running configuration file; Routing and ARP tables; Packet buffer.</td>
</tr>
<tr>
<td>ROM</td>
<td>Non-Volatile</td>
<td>Bootup code; Basic diagnostic; Limited IOS (ROM Monitor)</td>
</tr>
<tr>
<td>NVRAM</td>
<td>Non-Volatile</td>
<td>Startup configuration file</td>
</tr>
<tr>
<td>Flash</td>
<td>Non-Volatile</td>
<td>Cisco IOS</td>
</tr>
</table>
</section>
<section>
<h2>Behind a Router</h2>
<img src="http://i.imgur.com/n8J6bjl.jpg">
<p>Management (<em>out-of-band</em>) ports don't forward packets, router (<em>in-band</em>) interfaces do!</p>
<img src="http://i.imgur.com/W0h8gIt.png">
</section>
<section>
<h2>Cisco IOS Boot Process</h2>
<img src="http://i.imgur.com/pHOiSud.jpg" width="43%" height="43%">
</section>
<section>
<h2>Cisco IOS "show version"</h2>
<pre><code class="bash">Cisco3845Router# show version
Cisco IOS Software, 3800 Software (C3845-IPBASE-M),
Version 12.3(11)T7, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Sat 30-Jul-05 03:12 by dchih
ROM: System Bootstrap, Version 12.3(11r)T2, RELEASE SOFTWARE (fc1)
Cisco3845Router uptime is 10 weeks, 6 days, 9 hours, 30 minutes
System returned to ROM by power-on
System restarted at 05:09:07 CDT Thu Oct 20 2005
System image file is "flash:c3845-ipbase-mz.123-11.T7.bin"
Cisco 3845 (revision 1.0) with 419839K/104448K bytes of memory.
Processor board ID FTX0938A5PE
2 Gigabit Ethernet interfaces
27 Serial interfaces
1 ISDN Basic Rate interface
1 Subrate T3/E3 port
DRAM configuration is 64 bits wide with parity enabled.
479K bytes of NVRAM.
62720K bytes of ATA System CompactFlash (Read/Write)
Configuration register is 0x2102
(will be 0x2102 at the next reload)</code></pre>
</section>
<section>
<section>
<h2>Initial Config of a Cisco Router</h2>
<p>Pretty much the same as the switch we configured in Lesson 2:</p>
<ul>
<li>Assign a device name.</li>
<li>Set passwords.</li>
<li>Provide legal notification.</li>
<li>Save the configuration.</li>
<li>Verify the configuration.</li>
</ul>
</section>
<section>
<h2>Initial Config of a Cisco Router</h2>
<pre><code class="bash">Router>enable
Router#configure terminal
Ented configuration commands, one per line. End with CNTL/Z
Router(config)# hostname R1
R1(config)#
R1(config)#enable secret hlcs
R1(config)#
R1(config)#line console 0
R1(config-line)#password hlcsconsole
R1(config-line)#login
R1(config-line)#exit
R1(config)#
R1(config)#line vty 0 4
R1(config-line)#password hlcsvty
R1(config-line)#login
R1(config-line)#exit
R1(config)#
R1(config)#service password-encryption
R1(config)#
R1(config)#banner motd #
Enter TEXT message. End with the character '#'.
*****************************************************
WARNING: Lasciate ogni speranza, voi che vi loggate!
*****************************************************
#
R1(config)#
R1(config)#exit
R1#copy running-config startup-config
Destination filename [startup config]?
Building configuration...
[OK]
R1#</code></pre>
</section>
</section>
<section>
<section>
<h2>Configuring interfaces on Cisco IOS</h2>
<p>Interfaces on Cisco IOS have a <em>type-and-number</em> nomenclature.</p>
<ul>
<li>GigabitEthernet0/0 (G0/0); GigabitEthernet0/1 (G0/1)</li>
<li>Serial/0/0/0 (S0/0/0); Serial/0/0/1 (S0/0/1)</li>
</ul>
<pre><code class="bash" style="max-height: 250px;">R1#conf t
Enter configuration commands, one per line.
End with CNTL/Z.
R1(config)#
R1(config)#interface gigabitethernet 0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#description LAN del Corso Adv. Networking
R1(config-if)#no shutdown
%LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0,
changed state to up
R1(config-if)#exit
R1(config)#
R1(config)#interface g0/1
R1(config-if)#ip add 192.168.2.1 255.255.255.0
R1(config-if)#des LAN supplementare
R1(config-if)#no shut
%LINK-5-CHANGED: Interface GigabitEthernet0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1,
changed state to up
R1(config-if)#exit
R1(config)#
</code></pre>
</section>
<section>
<h2>Verifying the configuration</h2>
<pre><code class="bash">Router123# show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0 10.108.0.5 YES NVRAM up up
Ethernet1 unassigned YES unset administratively down down
Loopback0 10.108.200.5 YES NVRAM up up
Serial0 10.108.100.5 YES NVRAM up up
Serial1 10.108.40.5 YES NVRAM up up
Serial2 10.108.100.5 YES manual up up
Serial3 unassigned YES unset administratively down down
Router123#
Router123#ping 10.108.100.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.108.100.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
</code></pre>
</section>
</section>
<section>
<section>
<h2>Default Gateway in action</h2>
<img src="http://i.imgur.com/vIz6XYd.jpg">
<p>Routers have a <strong>minimum of two interfaces</strong>, each configured with an IP address of separate networks.</p>
<p>Most of the times the default gateway address of a network is <strong>the router interface address attached to the local network</strong>.</p>
</section>
<section>
<h2>Default Gateway on Cisco Switches</h2>
<p>We assign an IP address to the <strong>switch virtual interface (SVI)</strong>:</p>
<pre><code class="bash">S1(config)# interface vlan1
S1(config-if)# ip address 192.168.1.123 255.255.255.0
S1(config-if)# no shut</code></pre>
<p>If the switch needs to be accessed remotely:</p>
<pre><code class="bash">S1(config)# ip default-gateway 192.168.1.1</code></pre>
<p>Without a default gw, the response <strong>packets originating from the switch won't know how to exit the local network</strong>.</p>
</section>
</section>
<section>
<h1>End of Lesson</h1>
</section>
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