We will debug GRE tunnels which were set in the previous post. There are two routers, basic interface configuration on Serial1/0 ports and a Tunnel interface on each router.
R1#debug tunnel
When everything is good:
R1#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/21/36 ms
R1#
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.2 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP (PS) to decaps 200.0.0.2->200.0.0.1 (tbl=0,"default" len=124 ttl=254)
Tunnel0: GRE decapsulated IP packet (linktype=7, len=100)
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.2 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP
R1# (PS) to decaps 200.0.0.2->200.0.0.1 (tbl=0,"default" len=124 ttl=254)
Tunnel0: GRE decapsulated IP packet (linktype=7, len=100)
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.2 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP (PS) to decaps 200.0.0.2->200.0.0.1 (tbl=0,"default" len=124 ttl=254)
Tunnel0: GRE decapsulated IP packet (linktype=7, len=100)
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.2 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
R1#Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP (PS) to decaps 200.0.0.2->200.0.0.1 (tbl=0,"default" len=124 ttl=254)
Tunnel0: GRE decapsulated IP packet (linktype=7, len=100)
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.2 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP to classify 200.0.0.2->200.0.0.1 (tbl=0,"Default" len=124 ttl=254 tos=0x0)
Tunnel0: GRE/IP (PS) to decaps 200.0.0.2->200.0.0.1 (tbl=0,"default" len=124 ttl=254)
Tunnel0: GRE decapsulated IP packet (linktype=7, len=100)
What we see here:
We sent 5 packets to R2, R1 encapsulated 5 packets, and decapsulated 5 packets. Obviously, the decapsulated packets are the reply packets from R2.Wrong tunnel destination
With debug tunnel command, we will see after configuration change:R1(config-if)#tunnel destination 200.0.0.3
FIBtunnel: Tu0: cli request terminated early: no
FIBtunnel: Tu0: cli request generated fib update: IPv4 punt change no, IPv6 punt change no, mode change no
FIBtunnel: Tu0: GRE/IP (0) punt ipv4: no (lc no), ipv6 no (lc no) [BEFORE]
FIBtunnel: Tu0: GRE/IP (0) punt ipv4: no (lc no), ipv6 no (lc no) [AFTER]
FIBtunnel: Tu0: stacking IP 0.0.0.0 to Default:200.0.0.3
R1#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.3 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes.
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.3 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes.
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.3 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes.
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.3 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes.
Tunnel0: GRE/IP encapsulated 200.0.0.1->200.0.0.3 (linktype=7, len=124)
Tunnel0 count tx, adding 0 encap bytes.
Success rate is 0 percent (0/5)
Packets are encapsulated and sent, but no response from the other side.
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