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Outline à Host routing decision à Prefixes and physical networks
à Prefix matching à Router operating principles and addressing scenarios
Network Architecture
H2 H3
IP net 1
IP net 3 IP net 6
IP net 7
IP net 9 ATM CDN
H4
Ethernet
R5
R4
R3 xDSL
xDSL
Ethernet WIFI
Host
Logical subnet
R1
Router (Gateway)
Physical network
R2
Physical Network
IP Packets can be delivered directly
à Usually a data link network
à E.g., Ethernet, WLAN
Classful Prefixes and Physical Networks
200.2.1.0
205.1.4.0
205.1.4.0
205.1.4.3 205.1.4.4
205.1.4.1 205.1.4.2
200.2.1.254
205.1.4.253
200.2.1.1 200.2.1.2
Bridge
Router
Classless Prefixes and Physical Networks
131.1.1.0
131.1.4.0
131.1.4.0
131.1.4.3 131.1.4.4
131.1.4.1 131.1.4.2
131.1.1.254
131.1.4.253
131.1.1.1 131.1.1.2
Netmask: 255.255.255.0
Bridge
Router
Note: same netmask in a whole subnet
Classless Prefixes and Physical Networks
203.1.1.8
203.1.1.0
203.1.1.3 203.1.1.4
203.1.1.9
203.1.1.2
Router
203.1.1.10 203.1.1.14
Netmask: 255.255.255.248
Different Netmasks for the Same Network
203.1.1.16 255.255.255.248
203.1.1.0
255.255.255.240 203.1.1.8 203.1.1.3
203.1.1.2 203.1.1.12
203.1.1.17
203.1.1.1
203.1.1.18 203.1.1.20
Bridge
Router
Same LIS: Direct CommunicaFon
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 0
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 1 0 0 1 0 1 Source address 192.168.10.65
DesQnaQon address 192.168.10.101
Source netmask 255.255.255.192
Same prefixèsame LIS direct communicaFon
192.168.10.64 192.168.10.64
Bitwise AND
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 0
Different LISes: Involve Router
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 0 0
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 Source address 192.168.10.65
DesQnaQon address 192.168.10.132
Different prefixesèdifferent LIS communicaFon through router
192.168.10.64 192.168.10.128
Bitwise AND
1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0
Source netmask 255.255.255.192
Prefix Matching for Each Interface
203.1.1.8
203.1.1.0
203.1.1.3 203.1.1.4
203.1.1.9
203.1.1.2 Router
203.1.1.10 203.1.1.14
Netmask: 255.255.255.248 At most one will match
What If None Matches?
H2 H3
IP net 1
IP net 3 IP net 6
IP net 7 IP net 9
H4
130.192.1.0
R1
R2
R5
R4
R3
190.3.7.1
190.3.7.2
190.3.1.1
190.3.1.5
190.3.9.2
190.3.9.3
190.3.6.2
190.3.6.3
190.3.6.8
190.3.3.1 190.3.3.3
190.3.3.2
190.3.1.4
190.3.6.3
190.3.6.0
150.1.0.0 255.255.0.0
150.1.8.4
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
E.g., R5 rouFng a packet to H4
RouFng Table
DesQnaQon Next hop 190.3.1.0 255.255.255.0 190.3.3.2 190.3.7.0 255.255.255.0 190.3.3.2 190.3.9.0 255.255.255.0 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
R5’s Directly connected
H2 H3
H4
190.3.1.0
190.3.6.3 190.3.6.8
190.3.3.1
190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
R5
R1
R2
R5
R4
R3
190.3.1.0 255.255.255.0 190.3.3.2 190.3.7.0 255.255.255.0 190.3.3.2 190.3.9.0 255.255.255.0 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
H2 H3
H4 R1
R2
R5
R4
R3 190.3.6.8 190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
190.3.1.0 255.255.255.0
R1
R2
R5
R4
R3
190.3.6.0 255.255.255.0
150.1.0.0 255.255.0.0
190.3.9.0 255.255.255.252
190.3.3.0 255.255.255.0
190.3.9.4 255.255.255.252
R5
Variable Subne[ng
190.3.9.1 190.3.9.5
190.3.6.3
190.3.1.0 255.255.255.0 190.3.3.2 190.3.9.0 255.255.255.252 190.3.3.2 190.3.9.4 255.255.255.252 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
H2 H3
H4
H2 H3
H4
190.3.1.0
R1
R2
R5
R4
R3 190.3.6.3
190.3.6.8
190.3.3.1
190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
What If MulFple Entries Match? 190.3.9.1
R5 190.3.0.0 255.255.240.0 190.3.3.2
190.3.9.0 255.255.255.0 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
Longest Prefix Matching
H2 H3
H4
190.3.1.0
190.3.6.3 190.3.6.8
190.3.3.1
190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
R5 190.3.0.0 255.255.240.0 190.3.3.2
190.3.9.0 255.255.255.0 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
R1
R2
R5
R4
R3
H2 H3
H4
190.3.1.0
190.3.6.3 190.3.6.8
190.3.3.1
190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
R1
R2
R5
R4
R3
Default Net Route
R5 190.3.0.0 255.255.0.0 190.3.3.2
190.3.9.0 255.255.255.0 190.3.6.8 150.1.0.0 255.255.0.0 190.3.6.8
H2 H3
H4
190.3.1.0
190.3.6.3 190.3.3.1
190.3.3.2
190.3.6.0
150.1.0.0 255.255.0.0
190.3.7.0 190.3.9.0
190.3.3.0
Netmask: 255.255.255.0
R1
R2
R5
R4
R3
R5 190.3.0.0 255.255.0.0 190.3.3.2
190.3.9.0 255.255.255.0 190.3.6.8 0. 0.0.0 0.0.0.0 190.3.6.8
Default Route
R5
180.1.0.0 255.255.255.0
Routing Sequence In Summary
à Connected networks à Specific entries à Less specific, aggregated entries
à Default route