[c-nsp] Newbie traceroute question

[Hank Nussbacher]

On 09/02/2016 22:25, Nitzan Tzelniker wrote:

I now realize I was unclear.  I do not have an MPLS network.  I do not
have any MPLS defined.  I am not issuing an mpls traceroute comamnd.  I
am on a Cisco router and issue a traceroute to www.google.com:

RP/0/RSP0/CPU0:GP1#trace 64.233.167.103 
Wed Feb 10 07:24:31.794 IST

Type escape sequence to abort.
Tracing the route to 64.233.167.103

 1  83.97.88.93 61 msec  60 msec  60 msec
 2  ae0.mx1.ams.nl.geant.net (62.40.98.81) [MPLS: Labels 300576/20 Exp
0] 75 msec  74 msec  75 msec
 3  google.mx1.fra.de.geant.net (62.40.125.201) 76 msec  74 msec  76 msec
 4  google-gw.mx1.fra.de.geant.net (62.40.125.202) 74 msec  74 msec  74
msec
 5  216.239.56.20 75 msec
    216.239.56.104 74 msec
    216.239.56.20 74 msec
 6  216.239.57.194 [MPLS: Label 30768 Exp 4] 74 msec
    216.239.57.188 74 msec
    216.239.57.184 74 msec
 7  66.249.95.39 [MPLS: Label 25060 Exp 4] 79 msec
    209.85.251.178 77 msec  77 msec
 8  74.125.37.150 [MPLS: Label 27944 Exp 4] 81 msec
    74.125.37.103 80 msec
    74.125.37.97 83 msec
 9  209.85.242.165 80 msec
    216.239.42.98 81 msec
    209.85.246.135 81 msec
 10  *  *  *
 11 wl-in-f103.1e100.net (64.233.167.103) 80 msec  80 msec  80 msec

On hop 2, 6, 7 & 8 suddenly the traceroute output *includes *MPLS data
(label & exp).  I understand how traceroute works (am very familiar with
Richard's excellent preso), but I still haven't seen an answer to my
question.  Gert's was possibly the closest with "Nothing special in IOS
traceroute, but more "stupidity in general unix traceroute" - when
sending a TTL exceed ICMP packet, the LSR copies the label stack into
the ICMP packet, and traceroute *could* handle this."

Thanks again,
Hank

> Take a look on this
>
> http://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/26585-mpls-traceroute.html
> It use extention based on https://tools.ietf.org/html/rfc4950 
>
> Nitzan
>
> On Tue, Feb 9, 2016 at 10:06 PM, Matěj Grégr <igregr at fit.vutbr.cz
> <mailto:igregr at fit.vutbr.cz>> wrote:
>
>     Hi Hank,
>       you can check:
>     http://www.cisco.com/c/en/us/support/docs/ip/ip-routed-protocols/22826-traceroute.html
>
>     It doesn't answer your specific question about MPLS, but there are
>     some
>     useful information - which protocol is used by default, reply codes,
>     differences between Linux/Windows/Cisco, etc.
>
>     M.
>
>     On 02/09/2016 07:26 PM, Hank Nussbacher wrote:
>     > When doing a traceroute from a Cisco IOS, what is being done
>     under the
>     > hood so that sometimes I am able to see MPLS hops from within the
>     > traceroute?
>     >
>     > Thanks,
>     > Hank
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