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Designing Real-World Networks - Lesson 2

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Nicola Arnoldi

on 19 October 2017

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Transcript of Designing Real-World Networks - Lesson 2

Routing Packets!!
packets traveling from subnet A to subnet B be need to be
"routed"
switching is different! (packets that stay within one IP subnet)
routing sits at L3 ISO/OSI stack
based on L3 addressing
IPv4 Address
32 bit number
4.3 trillions unique addresses
binary vs. dotted decimal notation
128.10.173.46/16
100000000.00001010.
10110010.00101110
network part
host part
class B address
16 bits for network, 16 for host
network mask 255.255.0.0
Subnetting
partitioning major networks in smaller ones for better manageability and higher granularity
Major Networks (classful)
Class A
First Octet = 1-126
Network Bits = 8
Possible networks = 126
Host Bits = 24
Hosts per network = 2^24 - 2
Example = 8.8.8.8
Major Networks (classful)
Class B
First Octet = 128-191
Network Bits = 16
Possible networks = 16384 (2^16-2)
Host Bits = 16
Hosts per network = 2^16 - 2
Example = 166.70.10.23
Major Networks (classful)
Class C
First Octet = 192-223
Network Bits = 24
Possible networks = (2^24-2)
Host Bits = 8
Hosts per network = 2^8 - 2
Example = 192.168.2.15
Major Networks
Class D - E
Reserved for multicast
i.e. 224.0.0.1
And future use
Private vs. Public
some ranges are reserved for private networks
(not routed on the Internet)
10.0.0.0 - 10.255.255.255 (10.0.0.0/8)
172.16.0.0 - 172.31.255.255 (172.16.0.0/12)
192.168.0.0 - 192.168.255.255 (192.168.0.0/16)
Routing concepts
a routing device has three main "missions"
building its own routing database (routing table)
co-operating with neighboring routers in building a dynamic routing topology (optional)


properly
forwarding
packets to the correct destinations (next-hops)
control plane
data plane
performed in software
performed in hardware (ASICs)
ROUTING PROTOCOLS!
Routing decisions
made on a per-dest-address basis
routing database (routing table)
several routing protocols may participate in populating the routing table
dynamic vs. static routing (st. routing is often considered a routing protocol itself)
administrative distance
what do I find in the routing table?
O 192.168.2.96 [110/2] via 10.19.1.4, 1d08h, Vlan19
O 192.168.2.32 [110/2] via 10.19.1.2, 1d08h, Vlan19
O 192.168.2.128 [110/2] via 10.19.1.5, 1d08h, Vlan19
B* 0.0.0.0/0 [200/0] via 172.25.64.2, 4w4d
Routing protocols
ways of populating the routing table
routers consider connected and static routing as particular routing protocols
what if multiple routes exist from different RPs??
ADMINISTRATIVE DISTANCE
(lower is better)
Administrative distance
Administrative distance is the measure used by routers to select the best path when there are two or more different routes to the same destination from two different routing protocols
Administrative distance defines the reliability of a routing protocol
Dynamic routing protocols
distance vector vs. link state (pros and cons)
link state routers have knowledge of the full routing topology
distance vector talk only with neighbors
convergence, overhead
RIP, OSPF, EIGRP, BGP (Internal or External), IS-IS
if i receive a packet whose IP destination address matches one of my routing entries (if I have multiple, I consider the "longest match") let's forward it to this address (the next-hop) which has to be a connected address
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