[j-nsp] Traceroute via secondary IP

[Jason Koh]

Hi there

I noticed something strange when I traceroute via a Juniper M20. Here is the IP route and the interface of the destination output.

> show route 202.64.10.69 

inet.0: 202575 destinations, 908871 routes (202327 active, 22196 holddown, 781 hidden)
+ = Active Route, - = Last Active, * = Both

202.64.10.69/32    *[BGP/170] 00:51:05, localpref 100
                      AS path: 2706 I
                    > to 192.169.32.66 via fe-1/2/0.0, Push 6575

# show interfaces fe-1/2/0.0 
family inet {
    rpf-check {
        mode loose;
    }
    mtu 1500;
    address 192.169.34.97/30;
    address 192.169.34.101/30;
    address 192.169.32.65/30;

#traceroute 202.64.10.69     

Type escape sequence to abort.
Tracing the route to 202.64.10.69

  1 203.120.91.4 [MPLS: Label 694944 Exp 0] 28 msec 0 msec 4 msec
  2 192.169.34.141 [MPLS: Label 126784 Exp 0] 0 msec 0 msec 4 msec
  3 192.169.34.98 [MPLS: Label 6575 Exp 0] 32 msec 36 msec 32 msec
  4 202.64.4.189 32 msec *  32 msec

Notice that it is going via .98 instead of .66 as shown by the show route command. 

The reverse trace.

Tracing the route to scipk032-lo.pacific.net.sg (192.169.38.32)

  1  *  *  * 
  2 192.169.32.65 [MPLS: Label 119024 Exp 0] 32 msec 32 msec 32 msec
  3 192.169.34.137 36 msec 36 msec 36 msec
  4 203.120.91.32 32 msec *  32 msec

Any idea why this is so?


Jason Koh
Senior Network Engineer
Pacific Internet Ltd