TAILIEUCHUNG - Virtual Private Networks

Virtual private networks (VPNs) are another feature that firewalls have quickly adopted. Firewalls, by the very nature of their placement in the network design, represent a natural device to provide termination for LAN-to-LAN and in some cases remote-access VPNs. | Virtual Private Networks Virtual private networks VPNs are another feature that firewalls have quickly adopted. Firewalls by the very nature of their placement in the network design represent a natural device to provide termination for LAN-to-LAN and in some cases remote-access VPNs. The firewall separates a public network from a private network and provides network administrators with a policy-enforcement point. As with IDSs vendors include the ability to set up VPNs on a firewall as a common feature for any firewall device available on the market. All open source firewalls also provide accommodations for VPN traffic. To deal with VPNs firewalls must take into account a variety of new protocols. For IPsec-based VPNs the firewalls must provide for the capability of handling the two types of IPsec traffic Authentication Header AH and Encapsulated Security Payload ESP although AH is relatively obsolete and rarely used as a VPN transport. Each provides distinct challenges to firewalls to allow an IPsec VPN to be set up either to the firewall itself or through it to a dedicated VPN appliance. Other types of VPNs that many firewalls support include Layer 2 Tunneling Protocol L2TP as well as the Point-to-Point Tunneling Protocol PPTP . Finally many firewalls now also offer the ability to support an SSL VPN. Each is discussed in the following sections. IPsec VPNs IPsec-based VPNs have quickly become one of the most prevalent VPN technologies on the market. The IPsec RFCs call for two protocols AH and ESP. Both of these protocols can be used in one of two ways transport mode or tunnel mode. Authentication Header The AH protocol is used to provide connectionless integrity and data origin authentication for IP datagrams. In addition AH provides for protection against replay attacks. AH protects a variety of fields within the IP header and the modification of those fields by a firewall can result in the destination host discarding the packets because of an invalid AH .

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