Traceroute question.

Netstudent

OKay can someone please explain why this traceroute is doing this.

Router1

Router1#show ip route

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
O 10.10.10.8/30 [110/128] via 10.10.10.6, 00:30:20, Serial0/1
[110/128] via 10.10.10.2, 00:30:20, Serial0/0
C 10.10.10.2/32 is directly connected, Serial0/0
C 10.10.10.0/30 is directly connected, Serial0/0
C 10.10.10.6/32 is directly connected, Serial0/1
C 10.10.10.4/30 is directly connected, Serial0/1
C 192.168.1.0/24 is directly connected, Loopback0

Router2
Router2#show ip route
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
C 10.10.10.10/32 is directly connected, Serial0/0
C 10.10.10.8/30 is directly connected, Serial0/0
O 10.10.10.0/30 [110/128] via 10.10.10.5, 00:32:06, Serial0/1
C 10.10.10.4/30 is directly connected, Serial0/1
C 10.10.10.5/32 is directly connected, Serial0/1
C 192.168.1.0/24 is directly connected, Loopback0

Router3
Router3#show ip route

Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
C 10.10.10.8/30 is directly connected, Serial0/1
C 10.10.10.9/32 is directly connected, Serial0/1
C 10.10.10.0/30 is directly connected, Serial0/0
C 10.10.10.1/32 is directly connected, Serial0/0
O 10.10.10.4/30 [110/128] via 10.10.10.9, Serial0/1

The reason router2 and 3 only have one route to the learned subnet is because

Router3#show ip ospf int s0/0
Serial0/0 is up, line protocol is up
Internet Address 10.10.10.2/30, Area 0
Process ID 2, Router ID 192.168.1.3, Network Type POINT_TO_POINT, Cost: 80 <--here
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 192.168.1.1
Suppress hello for 0 neighbor(s)

Here is my confusion:

Router1#traceroute 10.10.10.9

Type escape sequence to abort.
Tracing the route to 10.10.10.9

1 10.10.10.6 12 msec
10.10.10.2 12 msec *

Router1#traceroute 10.10.10.9

Type escape sequence to abort.
Tracing the route to 10.10.10.9

1 10.10.10.2 12 msec
10.10.10.6 120 msec
10.10.10.2 16 msec

Now I realize that there are 2 routes to this subnet, load balancing. The learned subnet is only one hop away. So is that 3 separate packets all with a TTL of 1? Or is that one packet bouncing around? If it is sending 3 packets then why is it sending 3 packets out of the route via .2 but only 2 packets via .6 with an asterik? Could someone please explain this output and the asterik????? Thanks

dpocoroba

Now I realize that there are 2 routes to this subnet, load balancing. The learned subnet is only one hop away. So is that 3 separate packets all with a TTL of 1? Or is that one packet bouncing around? If it is sending 3 packets then why is it sending 3 packets out of the route via .2 but only 2 packets via .6 with an asterisk? Could someone please explain this output and the asterisk????? Thanks

The technique of using Traceroute will be to send out a UDP packet to some random destination port between 3343 - 33464 with a TTL 1

What you are seeing is the load balancing taking place in the switching mechanism. The reason they may seem oddly balanced is the face your only sending a few packets out. If you could generate a stream of traffic you should see it get closer to 50/50 in terms of interfaces to leave on. In this case its sending out with a TTL of 1 from the 1st int then the 2nd.

since it didn't receive a ICMP "port unreachable" it will then try a TTL of 2 and so on so forth.

The * you see in the middle when doing a traceroutes is a built in ICMP rate-limit for the IOS. Just because you see an * doesn't always mean the destination is unreachable, unless you only get * for results


HTH
DP