PT Bug?

AlceoAlceo Member Posts: 80 ■■□□□□□□□□
I have
separated by a router used as a default gateway.

For my understanding PCA shouldn't be able to ping PCB
For PCA, PCB is in the same subnet so it should use an ARP to learn it's MAC address, it shouldn't forward the packet to the router.

In PT PCA ping PCB, is this a bug or Am I missing something?


  • rob42rob42 Member Posts: 423
    What IP Addresses/Masks have you set on the Router interfaces?
    No longer an active member
  • Jon_CiscoJon_Cisco Member Posts: 1,775 ■■■■■■■■□□
    Can you watch the packets and see if the router is forwarding it. For me the best part of packet tracer was the ability to watch the network traffic to understand how it was moving.
  • AlceoAlceo Member Posts: 80 ■■□□□□□□□□
    Just to check if it was a bug I set up GNS3 with two Virtual Machines connected to two differerent LAN cards:

    To my surprise a ping from to worked just fine despite the subnet mask.

    Here is why: sends an ARP for and Router1 responds with the mac address of it's own interface facing

    Is this a Cisco thing or all routers do the same?
  • networker050184networker050184 Mod Posts: 11,962 Mod
    Depends on your device, version and config. That's called proxy ARP.
    An expert is a man who has made all the mistakes which can be made.
  • mikeybinecmikeybinec CCNA 200-120 Member Posts: 484 ■■■□□□□□□□
    I assume you mean this topology

    If you look at the routing table (sh ip ro) you'll see both networks are directly connected and network masks or Class A vs Class B, etc doesn't matter.. The router knows where to send the traffic

    Cisco NetAcad Cuyamaca College
    A.S. LAN Management 2010 Grossmont College
    B.S. I.T. Management 2013 National University
  • dontstopdontstop Member Posts: 579 ■■■■□□□□□□
    rob42 wrote: »
    What IP Addresses/Masks have you set on the Router interfaces?

    Interested in this too.
  • AlceoAlceo Member Posts: 80 ■■□□□□□□□□
    The one in the picture and
    The thing I was missing is the one indicated by networker, the proxy arp function.
Sign In or Register to comment.