---------- Forwarded message ---------- From: "Dillon Yang" To: Date: Sat, 3 Sep 2005 11:49:11 +0800 Subject: Re: Re: Tunneling over OSPF In this case, tunnel source must be a base physical interface which connetivity is independent from the area 0 , not logical one, or you get this: *Mar 1 02:19:06: %SYS-5-CONFIG_I: Configured from console by console *Mar 1 02:19:09: %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing *Mar 1 02:19:10: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state t o down *Mar 1 02:19:10: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on Tunnel0 from FULL to DOWN, Nei ghbor Down: Interface down or detached *Mar 1 02:19:18: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on OSPF_VL0 from FULL to DOWN, Ne ighbor Down: Interface down or detached *Mar 1 02:20:10: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state t o up *Mar 1 02:20:20: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on Tunnel0 from LOADING to FULL, Loading Done *Mar 1 02:20:36: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on OSPF_VL0 from LOADING to FULL, Loading Done *Mar 1 02:21:50: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0, changed state to down *Mar 1 02:21:59: %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing *Mar 1 02:22:00: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on Tunnel0 from FULL to DOWN, Nei ghbor Down: Interface down or detached *Mar 1 02:22:00: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state t o down *Mar 1 02:22:06: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on OSPF_VL0 from FULL to DOWN, Ne ighbor Down: Interface down or detached *Mar 1 02:23:00: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state t o up *Mar 1 02:23:21: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on Tunnel0 from LOADING to FULL, Loading Done *Mar 1 02:23:39: %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing *Mar 1 02:23:40: %OSPF-5-ADJCHG: Process 3, Nbr 1.1.1.1 on Tunnel0 from FULL to DOWN, Nei Remember: 1. the GRE is just an additional PDU like this (20bytes)TRANSIT packet header(Transit source address, Transit destination address) (4byets)GRE packet header Your ORIGINAL IP header(GRE source address, GRE destination address) In any case, you'd better set ip mtu to 1500-20-4=1476. 2. For OSPF neighborhood, the GRE source address and the GRE destination address should be on the same subnet. So, you may config like this: ! interface Tunnel 0 ip address tunnel source or tunnel destination ip mtu 1476 ! router ospf 7 network 0.0.0.0 area 0 ! ---