Exercises

1
Exercises

• Network design and configuration

2
Transparent NAT
3
Before NAT
WebServer
188.54.20.2
router
firewall
LAN HUB
LAN HUB
10.20.0.0/16
188.54.20.0/24
4
After NAT OK?
188.54.20.2
WebServer
10.20.0.2
router
firewall
LAN HUB
LAN HUB
188.54.20.0/24
10.20.0.0/16
188.54.20.2
10.20.0.2
5
After NAT Need ARP fix!
188.54.20.2
WebServer
MACIF2
10.20.0.2
MACIF1
router
firewall
LAN HUB
LAN HUB
188.54.20.0/24
10.20.0.0/16
MACIF1 ARP(188.54.20.2)
188.54.20.2
10.20.0.2
6
RFC 1027

• Using ARP to implement transparent subnet
  gateways
• Describes transparent subnet division using ARP

7
Before
Machine C 10.4.5.2 MACC
HUB
Machine A 10.4.5.1 MACA
Machine B 10.4.5.3 MACB
Machine D 10.4.5.4 MACD
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After
Machine C 10.4.5.2 MACC
HUB
Machine A 10.4.5.1 MACA
HUB
gateway
MACgwright 10.4.5.254
Machine B 10.4.5.3 MACB
Machine D 10.4.5.4 MACD
MACgwleft 10.4.5.253
9
Gateway ARP

• Left
• Macgwleft ARP(10.4.5.2)
• Macgwleft ARP(10.4.5.4)
• Macgwleft ARP(10.4.5.253)
• Right
• Macgwright ARP(10.4.5.1)
• Macgwright ARP(10.4.5.3)
• Macgwright ARP(10.4.5.254)

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Gateway routes

• Route to host 10.4.5.1 via 10.5.4.253
• Route to host 10.4.5.3 via 10.5.4.253
• Route to host 10.4.5.2 via 10.5.4.254
• Route to host 10.4.5.4 via 10.5.4.254

11
ARP for load balancing

• N systems can handle same request
• Use ARP proxy to provide load balancing

12
Network card in promiscuous mode

• What does it mean?
• What does it imply?

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