Virtual Private Networks Warren Toomey
Available WAN Links
Dedicated Links: very expensive, fixed endpoints Packet-Switched: expensive, fixed endpoints but some choice What if we need a cheaper alternative, or one where the endpoints can move around? – We have to use the Internet – Our traffic goes through other peoples’ routers
A Dilemma We want to interconnect parts of our enterprise over long distances – But we are using a public network to do so
Virtual Private Network What we want is a WAN link: link with an IP address at each end, and one which carries traffic that others cannot see VPN: Virtual Private Network Virtual: Information within a private network is transported over a public network Private: The traffic is encrypted to keep the data confidential
Benefits of VPNs Cost Savings: cheaper than dedicated links Scalability: use existing Internet connection Security: encryption ensures traffic is secure
VPN Tunnels A VPN tunnel acts like a WAN link In reality, it is a collection of public routers and LAN/WAN links Traffic enters the tunnel, and traverses the tunnel until it reaches the other end The traffic needs to be encapsulated: – Placed into the network protocol used on the physical links of the tunnel – Example: IP packets are encapsulated in IP packets
VPN Tunnels
VPN Encryption
GRE: VPN Technology Generic Routing Encapsulation VPN technology developed by Cisco Set up on two routers with public IP addrs To form a tunnel between them – Carrying private IP traffic over public Internet
GRE Example R1 has public IP address R2 has public IP address R1 has a private LAN /24 R2 has a private LAN /24
GRE Example We want to route traffic between the private LANs. We need a tunnel between them The GRE tunnel acts like a WAN link – Each end has an “interface” with an IP address – Just like a s0/0/0 with an IP address
GRE Configuration We need static routes on each router. Cannot advertise with a routing protocol R1(config)# ip route R2(config)# ip route Note: we use the private IP addresses in the static route