300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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QuestionQ189

VPN Technologies

A customer asked for a GRE tunnel across the provider network between two customer sites, using loopback to conceal the internal networks. Which configuration on R2 creates the tunnel to R1?

  • A R2(config)#interface Tunnel1 R2(config-if)#ip address 172.20.1.2 255.255.255.0 R2(config-if)#ip mtu 1400 R2(config-if)#ip tcp adjust-mss 1360 R2(config-if)#tunnel source 192.168.20.1 R2(config-if)#tunnel destination 192.168.10.1
  • B R2(config)#interface Tunnel1 R2(config-if#ip address 172.20.1.2 255.255.255.0 R2(config-if)#ip mtu 1400 R2(config-if)#ip tcp adjust-mss 1360 R2(config-if)#tunnel source 10.10.2.2 R2(config-if)#tunnel destination 10.10.1.1
  • C R2(config)#interface Tunnel1 R2(config-if)#ip address 172.20.1.2 255.255.255.0 R2(config-if)#ip mtu 1500 R2(config-if)#ip tcp adjust-mss 1360 R2(config-if)#tunnel source 10.10.2.2 R2(config-if)#tunnel destination 10.10.1.1
  • D R2(config)#interface Tunnel1 R2(config-if)#ip address 172.20.1.2 255.255.255.0 R2(config-if)#ip mtu 1500 R2(config-if)#ip tcp adjust-mss 1360 R2(config-if)#tunnel source 192.168.20.1 R2(config-if)#tunnel destination 10.10.1.1
Explanation

GRE encapsulates customer traffic between provider-reachable tunnel endpoints. R2 therefore uses 10.10.2.2 as its tunnel source and R1’s 10.10.1.1 as its tunnel destination; the internal 192.168.x.x addresses are not the outer tunnel endpoints. A reduced tunnel IP MTU of 1400 and TCP MSS adjustment of 1360 help prevent fragmentation caused by GRE encapsulation.

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