I have a small network here. The connection from router 1 to router 3 is relevant. I have two questions in one. On the one hand I would be interested, why at Cisco between the routers always this red connection arises. Does this have something to do with WANs? My other question relates to traceroute. The command gives the next router of the connection. How about this example? I am somewhat confused, since I can not exactly assign which IP now belongs to which router (I think this red connection irritates me easy). What the command does is clear to me. Only I can not find straight in the network naming.

My approach would be: Traceroute The output should then be: with XY secs with XY secs

Is this right? Is the router IP the respective input IP?

Sorry for my confusion. I hope you could help me. Thank you very much!

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PS: I have often seen this serials S1 and S0, but what are the differences between this serials, why are there two serials? If I imagine how to connect two routers I would use only one serial. so why are there two?

1 Answer 1


Traceroute is used to determine the path between hosts, not between networks. From the PC on the left, you would traceroute to the PC on the right, 192.17.5.x. the result would show you the path used to get from one PC to the other (subject to all the usual disclaimers).

Routers can (and often do) have multiple interfaces. In your diagram, for example, multiple interfaces allow the packet to take an alternate path if one becomes unavailable. That's what routing is all about. It's true, if you only have two routers, you only need one serial interface. But that's not the real world.

I'm afraid I don't understand your question about colors.

  • Thanks for the answer. The task was about routing. There should be specified what can be issued with a traceroute command. Thus, several paths are possible. That's right. I've narrowed this down, since my question is somewhat more elementary. Times I would like to use routing between 2 routers. In the picture Router 1 and Router 3. How is the command for this? Let's say we start routing on router 1: Ip route S1 or Ip route S0 Which of these would be correct? I would say: ip route S1, since we go over S1 after "outside"? Commented Aug 30, 2017 at 18:04
  • If you are only using static routes, you should use the command "ip route" Normally, you specify the next hop address, not the interface. The problem with static routes is it does not allow any redundancy, if for example, the link between R1 and R3 fails. That's why we use routing protocols.
    – Ron Trunk
    Commented Aug 30, 2017 at 18:23
  • Don't forget to add a route on R3 to get back to
    – Ron Trunk
    Commented Aug 30, 2017 at 18:33
  • Ok this helps me. Sorry I would like to up vote your answer, because its good. But I have not now the permission. If I understand it right the command is: ip route <destination> <subnet> <next hob> ??? I was confused, because in many Internet articles it was like this (ip route"), but in other ressources it was "ip route". But in my opinion X.X.7.2 dont makes sence, because the next hob is X.X.7.1 Commented Aug 31, 2017 at 8:55
  • "Don't forget to add a route on R3 to get back to", Yes thats right too. From the one direction to the other and switched. Commented Aug 31, 2017 at 8:58

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