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below is a capture of the configuration. R1 can ping the other two routers but R2 and R3 can't ping each other. Any idea what my issue could be? Screen Shot 2018-09-03 at 2.57.00 PM.pngenter image description here

Router2#sh run

interface GigabitEthernet0/0 
ip address 192.168.2.2 255.255.255.240 
duplex auto 
speed auto

Router1: 

interface GigabitEthernet0/0 
ip address 192.168.2.1 255.255.255.240 
duplex auto 
speed auto 
! 
interface GigabitEthernet0/1 
no ip address 
duplex auto 
speed auto 
shutdown 
! 
interface Serial0/0/0 
ip address 192.168.2.17 255.255.255.240 
clock rate 2000000

Router3: 

interface Serial0/0/0 
ip address 192.168.2.18 255.255.255.240 
! 
interface Serial0/0/1 
no ip address 
clock rate 2000000 
shutdown 
! these are the changes made to the routers
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8
  • We need more information. Please edit your question to include the router configurations. – Ron Maupin♦ Sep 3 '18 at 20:11
  • Unfortunately, homework and test questions are off limits on this site. This question is best asked over on Super User – Jesse P. Sep 3 '18 at 20:25
  • Router2#sh run interface GigabitEthernet0/0 ip address 192.168.2.2 255.255.255.240 duplex auto speed auto Router1: interface GigabitEthernet0/0 ip address 192.168.2.1 255.255.255.240 duplex auto speed auto ! interface GigabitEthernet0/1 no ip address duplex auto speed auto shutdown ! interface Serial0/0/0 ip address 192.168.2.17 255.255.255.240 clock rate 2000000 Router3: interface Serial0/0/0 ip address 192.168.2.18 255.255.255.240 ! interface Serial0/0/1 no ip address clock rate 2000000 shutdown ! these are the changes made to the routers – Diallo Abdoul Sep 3 '18 at 20:28
  • Without configs, we cannot say. Most common issues: (a) R1 not configured for routing. (b) routing isn't setup correctly. – Ricky Sep 3 '18 at 20:30
  • I just sent the configuration. All I did was assigning IPs to the routers, nothing else. I just don't know the routers to the extremities do not ping each other – Diallo Abdoul Sep 3 '18 at 20:35
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Since you didn't include the full router configurations, I must assume you do not have any static routes or routing protocols configured.

Routers learn routes in three ways:

  • Directly connected networks
  • Statically configured routes
  • Dynamically through a routing protocol

Router 2 has no knowledge of the network on the other side of Router 1, and the same things holds for Router 3. If a router has a packet with a destination to an unknown network, it drops the packet. Router 2 doesn't know how to reach the network with Router 3, so it drops packets destined for Router 3, and Router 3 has no knowledge of the network of Router 2, so it drops packets destined for Router 2. That is how it should be.

You will either need to configure static routes on Router 2 and Router 3, or you will need to run a common routing protocol on your routers.

On router 2, you can create a static route:

ip route 192.168.2.16 255.255.255.240 192.168.2.1

On Router 3, you can create a static route:

ip route 192.168.2.0 255.255.255.240 192.168.2.17
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  • Thank you so much Ron, it works now. So, if I understood your answer. Although R2 and R3 are directly connected to R1, I still need to configure a routing protocol? Why can't R2 and R3 learn routes from R1, or it's only on certain situations that can be possible? – Diallo Abdoul Sep 3 '18 at 21:40
  • R2 and R3 can learn routes from R1, but you would need to run a routing protocol for that. I explained the three ways that routers learn routes. R2 is not connected to the R1-R3 network, so method 1 is out. That means that you either need to statically configure the route, or you need to configure a routing protocol (RIP, EIGRP, OSPF, IS-IS, etc.). – Ron Maupin♦ Sep 3 '18 at 21:47
  • Okay got it now, thx again. – Diallo Abdoul Sep 3 '18 at 21:54
4

As per diagram R1 can ping both R2 and R3 beacuse both networks are directly connected networks .

To ensure ping successful from R2 & R3 routing need to be configured in R2 & R3 router

R2 Router

IP route 192.168 .2.18 255.255.255.255 pointing towards gateway 192.168.2 .1

R3 Router

IP route 192.168 .2.2 255.255.255.255 pointing towards gateway 192.168.2.17

I

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  • 1
    ARP isn't relevant for routing. – Zac67 Dec 1 '20 at 5:28
  • 1
    Yes , ARP relevant for routing correct . But to forward packets to end devices in directly connected network . Packet forwarding desicion is made with reference to ARP table . – Sagar Uragonda Dec 1 '20 at 5:38
  • 1
    What new information did your answer provide that the first one didn't? Maybe you can write something about dynamic routing protocols? – manish ma Dec 1 '20 at 6:22

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