GRE – Generic Routing Encapsulation a Cisco VPN for multiple protocols

GRE generic routing encapsulation GRE is a Cisco proprietary VPN it’s a tunneling arrangement so it allows two sites to communicate information back and forth over a public internet connect so gr e because it’s generic allows any type of any protocol data so it could be an ipv4 packet could be ipv6 could be Apple talk which is what the Macintosh operating system works could be IP X which is something that a Novell system would use so the fact that it’s generic allows for any type of a protocol container to be sent back and forth GRE however is not a secure VPN so it encapsulates data but it doesn’t have the security built in nonetheless it was better stipulates private communication over a public internet acquaintance so the internet connection itself so here we’ve got router r1 and rotor r2 connected through an interconnect connection it might be a DSL connection maybe something through your phone company or it could be a cable tie doesn’t matter it’s a public internet associate but we make a private passageway through the GRE tunneling system so the IP addresses sometimes get a little bit confusing so that’s what I wanted to show you here so we’ve got router r1 here the actual router interface IP address is 209 165 201 1 but from the perspective of r1 because we’ve created a GRE tunnel we give the illusion that the IP interface of the router is actually 192 168 to 1 which is really the beginning of the designation but if you look over here which I know it’s hard to see when you look over here at the show interface tunnel zero output it said that the Internet address is 192 168 to 1 well that internet address is truly the entry into the tunnel itself it says down here tunnel root so that’s the source address and it’s really the source address of the router the passageway beginning is right here that s zero zero zero interface of our one tunnel source 209 165 201 one that’s this address here so the passageway destination then from the point of view of our one is going to be this IP address here our select interface so 209 165 201 2 is going to be the passage end so truly “when youre doing” the show in our face tunnel the IP address is that it’s talking about for the tunnel generator in the tunnel destination are genuinely the IP addresses of the routers themselves though the legion addresses of the boundary of the router that’s using the tunneling method so that was often the perspective of r1 r2 over here will have the opposite perspective so our select IP address is going to be 192 168 2 2 because that’s this side of the passageway and then the source the passage beginning address is going to be its own interface so 209 165 201 2 and then this the tunnel destination is going to be this interface over here 209 165 201 1

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