1. email or call for office visit Chapter 6 - IPsec (IP Secure)
ECE-6612
Prof. John A. Copeland
Office: Klaus 3362
or call for office visit
Chapter 6 - IPsec (IP Secure)
(note: includes copies of figures from Chap. 6 of
“Network Security Essentials, Applications and Standards”
by William Stallings)
2/15/16

2. Each LAN Connects to Internet via a Router
Link
(LAN)
Link
(P-P)
Link
(P-P)
Link
(LAN) 2

3. The Internet is a Router Network
In an Router Network, circuits are defined by entries in the
Routing Tables along the way. These may be Static (manually
set up) or Dynamic (set up according to an Algorithm in the
Router). B IP
A to D A C 1 2 3
E’net 6 E 4 5 7 D
Station
( on a LAN)
Token Ring A
Local Connection 1
Router
Trunk or Long-Haul 3

4. Optimal Paths From Router 1
OSPF Defines Router 1's Sink Tree 4 E 3 A 5 C D B 1 7 6 2 A
Host (e.g., PC, Webcam, ...)
Local Connection 1
Backbone Connections
Router 4

5. Interconnected ASes 3b 1d 3a 1c 2a
AS3
AS1
AS2 1a 2c 2b 1b
Intra-AS
Routing
algorithm
Inter-AS
Forwarding
table 3c
Forwarding table is configured by both intra- and inter-AS routing algorithm
Intra-AS sets entries for internal dests
Inter-AS & Intra-As sets entries for external dests
OSPF
BGP
BGP for “which Internet gateway” (1b or 1c)
Network Layer

6. Hurricane Electric Internet Services
Cogent Comm.
Telesonera
GT-Fr.
GT-U.S.
Internet2
Hurricane Electric

7. Router http://www.cnn.com/ Find: IP address, TCP port
Router Ethernet Address
Browser
Web Server
Application
Application
Layer
Layer
(HTTP)
Router
(HTTP)
Transport
Transport
Buffers Packets that
Layer
Layer
need to be forwarded
(TCP,UDP)
(TCP,UDP)
(based on IP address).
Port 31337
Port 80
Network
Network
Layer (IP)
Layer (IP)
IP Address
Network
Network
IP Address
Layer
Layer
Token Ring
E'net Data
Token Ring
E'net Data
Link Layer
Link Layer
Data-Link Layer
Data Link Layer
Ethernet
Token Ring
E'net Phys.
Token Ring
Phys. Layer
Phys. Layer
Layer
Phys. Layer 7

8. Starting a TCP Client-Server Connection
Your computer has been configured with IP addresses for:
1) Itself ( ),
2) Local Router ( ),
3) Domain Name Server ( )
4) it’s subnet Mask (/24 or ).
The IP Broadcast Address is (IP address) bitwise-OR (~Mask)
| =
Its Ethernet, or WiFi, MAC Address is built into the adapter.
After you type “ into your browser, your computer has to know or discover (it assigns client port number):
1) IP address of “ and TCP port number (80),
2) Ethernet (MAC) address to use for DNS server,
3) Ethernet (MAC) address to use for “ 8

9. Checking, Setting the Network Configuration
~ copeland$ ifconfig en0 # Windows use CMD, “ipconfig”
en0: flags=8963<UP,BROADCAST,SMART,RUNNING,
PROMISC,SIMPLEX,MULTICAST> mtu 1500
ether 00:1f:5b:ef:8a:cc
inet netmask 0xffffff00
broadcast
media: autoselect (100baseTX <full-duplex>)
status: active

10. Preparations for a TCP/IP Connection
ARP “who has (LAN broadcast)
ARP “ is at 00:0f:66:c1:0f:ae”
DNS (UDP:53) “ resolve
DNS “ IP address is
ARP “who has
ARP “ is at 00:0f:66:c1:0f:ae”
TCP ( SYN ) to port 80
TCP (SYN-ACK) from
Red – Ethernet Frame
Black – IP Datagram
You need MAC address of
Router since CNN is off LAN
MAC addresses are cached for 30 seconds
Your Host
00:1f:5b:ef:8a:cc
DNS
Router “
TCP port 80
Each type of response might be spoofed or falsified 10

11. Address Resolution Protocol (ARP)
ARP is a Link-Layer protocol (e.g., Ethernet, WiFi). It can be used for Network Layer protocols other than IP.
When a host needs to find the MAC Address (e.g., Ethernet, WiFi) of corresponding to an IP address, it broadcasts an ARP Request (MAC broadcast address is ff:ff:ff:ff:ff:ff).
If the IP address is not local, ARP is used to find the MAC address of the Local Router (aka Gateway Router).
MAC addresses found by ARP are cached for 30 seconds, so during an IP connection, there will be ARPs every 30 seconds.
ARP Response spoofing can be used to set up a Man-in-the-Middle attack. Critical IP:MAC associations (e.g., Router, DNS) can be “nailed up” by manually putting permanent lines in the ARP table.
When a host first comes on line, it issues a Gratuitous ARP for its own IP address to see if there is another host using the same IP address. 11

12. WireShark Packet Capture - Browsing www.cnn.com
Notes: Ethernet Addresses have the first 3 bytes (of 6) translated into the interface manufacturer’s name (Apple_Computer is my PowerBook, Cisco_Linksys is the router).
in my PowerBook,
is the router,
if the DNS server, and is
In this case, the Apple PowerBook has code that detects that the DNS IP is outside the local area network, so it ARPs for the Ethernet address of the router ( ). It caches this address for 30 seconds, so it does not have to ARP again for the CNN IP address. 12

13. You will find information on Wireshark filters, and a input file:
For information on installing "Wireshark" and other Network Utility Programs, go to:
You will find information on Wireshark filters, and a input
file:
capture-example.cap in 13

14. Internet Layer Security (IPsec)
Rolf Oppliger, "Internet Security: Firewalls and Beyond," p92, Comm. ACM 40, May 1997
The Internet Engineering Task Force (IETF) •
Internet Security Protocol working group
standardized an IP Security Protocol (IPsec) and
an Internet Key Management Protocol (IKMP).
objective of IPsec is to make available cryptographic
security mechanisms to users who desire security.
mechanisms should work for both the current version
of IP (IPv4) and the new IP (IPv6).
should be algorithm-independent, in that the
cryptographic algorithms can be altered.
should be useful in enforcing different security
policies, but avoid adverse impacts on users who do
not employ them. 14

15. IPsec Authentication Header (AH)
Transport Mode
Transport
Mode Rb
B - Bob
Tunnel Mode
A - Alice 15

16. Encapsulated Secure Payload (ESP) Transport Level Security
(not TLS = Transport Layer Sec.) 16

17. Virtual Private Network (VPN)
IPsec ESP - Tunnel Mode
Virtual Private Network (VPN) 17

18. Security Associations
Transport, Host-Host
Tunnel, Gateway-Gateway (Routers) 18

19. Rb is the Gateway Router to B
Internet Layer Security (IPsec)
Normal Internet Protocol (IP)
IP Header, A to B TCP Header Application Header Data
IPsec Authentication Header (AH) - Transport and Tunnel Modes
IP Header, A to B AH TCP Header Application Header Data
IP Hdr, A to Rb AH IP Hdr A to B TCP Hdr Application Header Data
Authenticated
IPsec Encapsulated Secure Payload (ESP)
IP Header, A to Rb ESP Header TCP Header Application Header Data
Encrypted
IPsec Encapsulated Secure Payload (ESP) with AH
IP Header, A to Rb AH ESP Header TCP Header Application Hdr Data
Encrypted
Authenticated
Rb is the Gateway Router to B 19