Transcript Web Security

IPSec VPN
Chapter 13 of Malik
Outline
• Types of IPsec VPNs
• IKE (or Internet Key Exchange) protocol
http://sce.uhcl.edu/yang/teaching/.
../VPN.ppt
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Types of IPsec VPNs
•
Site-to-site (aka LAN-to-LAN) IPsec VPN
Figure 13-1
Question: no concentrator?
•
Remote-access client IPsec VPN
Figure 13-2
Unique challenges: (see p.317)
1.
IPsec clients use unknown-to-gateway IP addresses to connect to the
gateway
2.
Client’s IP address assigned by the ISP is not compatible with the
private network’s addressing.
3.
The clients must use the DNS server, DHCP server, and other such
servers on the private network.
4.
PAT can no longer function as normal (because ESP encrypts all the
port info in the TCP or UDP header).
http://sce.uhcl.edu/yang/teaching/.
../VPN.ppt
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Phases of IPsec
1.
2.
Connection initiated
IKE main mode or aggressive mode
Results:
a.
creation of an IKE Security Association (SA) between the two
IPsec peers
b.
A set of 3 session keys are established
•
Quick mode
Results:
a.
creation of two IPsec SAs between the two peers (incoming SA
and outgoing SA)
b.
Generate a pair of IPsec keys (one for each of the SAs)
1.
Data communication (using ESP or AH)
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../VPN.ppt
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IPsec Negotiation using IKE
•
P.279: Authentication methods vs modes
Preshared
key
Digital
signature
Encrypted
nonces
Main mode
Aggressive
mode
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IPsec Negotiation using IKE
Example 1: Main mode using preshared key
authentication followed by Quick mode negotiation
pp.280-298
Example 2: Main mode using DS authentication followed
by Quick mode negotiation
pp.298-302
Example 3: Aggressive mode using Preshared key
authentication (followed by Quick mode negotiation)
pp. 302-306
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../VPN.ppt
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