Traceroute issue Cisco

[faizan_barmare]

Hi

When I ran traceroute command from the cisco device, I am getting different outputs every time. The path is the same, but some hop is shown sometimes and sometimes not.

But when we check traceroute on MikroTik device, it shows the same path on every time we run traceroute.

#traceroute 218.248.240.23
Type escape sequence to abort.
Tracing the route to ns1.bsnl.in (218.248.240.23)
VRF info: (vrf in name/id, vrf out name/id)
1 *
103.27.170.24 0 msec 0 msec
2 * * *
3 * * *
4 218.248.232.1 [AS 9829] 20 msec 20 msec 20 msec
5 * * *
6 * * *
7 * * *
8 * * *
9 * * *
10 * * *
11 * * *
12 * * *
13 * * *
14 * * *
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
21 * * *
22 * * *
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *

#traceroute 218.248.240.23
Type escape sequence to abort.
Tracing the route to ns1.bsnl.in (218.248.240.23)
VRF info: (vrf in name/id, vrf out name/id)
1 * * *
2 218.248.235.225 [AS 9829] 0 msec
218.248.235.157 [AS 9829] 0 msec *
3 * * *
4 218.248.232.1 [AS 9829] 20 msec 20 msec 24 msec
5 * * *
6 * * *
7 * * *
8 ns1.bsnl.in (218.248.240.23) [AS 9829] 20 msec * *

#traceroute 218.248.240.23
Type escape sequence to abort.
Tracing the route to ns1.bsnl.in (218.248.240.23)
VRF info: (vrf in name/id, vrf out name/id)
1 103.27.170.24 4 msec * 0 msec
2 218.248.235.225 [AS 9829] 4 msec 4 msec
218.248.235.157 [AS 9829] 0 msec
3 * * *
4 218.248.232.1 [AS 9829] 20 msec 20 msec 20 msec
5 * * *
6 * * *
7 * * *
8 * * *
9 * * *
10 * * *
11 * * *
12 * * *
13 * * *
14 * * *
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
21 * * *
22 * * *
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *

#traceroute 218.248.240.23 source port-channel3
Type escape sequence to abort.
Tracing the route to ns1.bsnl.in (218.248.240.23)
VRF info: (vrf in name/id, vrf out name/id)
1 * * *
2 * * *
3 * * *
4 218.248.232.1 [AS 9829] 20 msec 24 msec 20 msec
5 ns1.bsnl.in (218.248.240.23) [AS 9829] 20 msec * *

Thanks in advance.

[Richard Burts]

We do not know much about the topology of either network or about the routing policies or the security policies of either network. This makes it difficult to give good advice. Here are some observations based on the limited information available to us:

- we are presented with the output of 4 traceroute to the same destination address. One of the 4 specifies a source address. It is not clear whether the specified source address is different from the default source or is the same as the default source address. Perhaps some of the variability is due to the change of source address.

- all 4 traceroute arrive at the same address at hop 4 218.248.232.1. So behavior within the source AS is consistent. All variability occurs within the remote AS. 

- we are told that behavior is different when traceroute from MikroTik device. I am not familiar with that device and do not know how it performs traceroute. But I am guessing that it may perform traceroute using ping (ICMP) packets as many devices do. We do not know which Cisco device this is, but we do know that most Cisco devices perform traceroute using UDP packets. Perhaps some of the difference is based on different policies in the remote AS for evaluating ICMP and UDP packets.

[faizan_barmare]

This trace-route was run in continuous succession one after another. There are no changes in routing policies or security policies.
- Hence there is no change of source address. So, one of the 4 trace-route specifies a source address, the specified source address is the default source address.
- Even within the remote AS, there were no routing policy changes when trace-route was run.
- MikroTik can do UDP MTR also but the output is the same as that of ICMP.