158 BigIron RX Series Configuration Guide53-1001810-01Configuring IP parameters7NOTEThe encapsulated packets sent on a GRE tunnel have the DF bit set. Setting a GRE tunnel MTU tobe greater than 1476 will cause the encapsulated packet to be greater than 1500 bytes. This maycause the transit routers to drop the encapsulated packet if that transit router's IP MTU is 1500bytes (a typical default MTU value) since transit routers can not fragment a GRE packet.Configuring a GRE IP tunnelTo configure a GRE IP Tunnel, the following parameters must be configured:• Tunnel interface• Source Address for the Tunnel• Destination address for the Tunnel• GRE Encapsulation• Loopback address for the Tunnel (required for de-encapsulation)• IP address for the TunnelNOTESustained rates of small packet sizes may affect the ability of a 10 gigabit Ethernet port to maintainline rate GRE encapsulation and de-encapsulation performance.Configuring a tunnel interfaceTo configure a tunnel interface, use a the following command.BigIron RX(config)# interface tunnel 1BigIron RX(config-tnif-1)Syntax: interface tunnel The variable is numerical value that identifies the tunnel being configured.Configuring a source address for a tunnel interfaceTo configure a source address for a specific tunnel interface, enter the following command.BigIron RX(config)# interface tunnel 1BigIron RX(config-tnif-1)tunnel source 35.0.8.108Syntax: tunnel source >The variable is source IP address being configured for the specified tunnel.Configuring a destination address for a tunnel interfaceTo configure a destination address for a specific tunnel interface, enter the following command.BigIron RX(config)# interface tunnel 1BigIron RX(config-tnif-1)tunnel destination 131.108.5.2Syntax: tunnel destination The variable is destination IP address being configured for the specified tunnel.
