Router can ping host, but host can't ping router?

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Energize

Caporegime
Joined
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Location
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I'm having a strange situation that I can't figure out. I have a windows 10 pc (10.1.1.100) connected to a switch connected to a router (10.1.1.1) which is set as the default gateway. This router has another interface (10.7.1.0) which connects to another router (10.7.1.1), now this other router can ping the host just fine, but any attempt to ping 10.7.1.1 or even 10.7.1.0 from the host end times out every time. What could potentially be causing this issue?

Clearly both the router and host know how to get to each other otherwise the ping from the router to the host would fail. :confused:
 
10.7.1.0 is not a usable IP address for a start. What IP address is the second interface on your first router using really?

What subnet masks are you using on each device?
 
BigT said:
10.7.1.0 is not a usable IP address for a start. What IP address is the second interface on your first router using really?

What subnet masks are you using on each device?
Click to expand...

These are the interfaces on the first router. The subnet mask is /24 on the 10.1.1.0 network and /31 on the 10.7.1.0 PPP network.

Code: 
ROUTER-1#show ip interface brief

Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            10.1.1.1        YES NVRAM  up                    up
FastEthernet0/1            10.5.1.0        YES NVRAM  up                    up
Serial0/2/0                10.7.1.0        YES NVRAM  up                    up


This is the second router:

Code: 
ROUTER-3#show ip interface brief

Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            10.3.1.1        YES NVRAM  up                    up
FastEthernet0/1            10.6.1.1        YES NVRAM  up                    up
Serial1/0                  10.4.1.1        YES NVRAM  up                    up
Serial1/1                  10.7.1.1        YES NVRAM  up                    up
Serial1/2                  unassigned      YES NVRAM  administratively down down
Serial1/3                  unassigned      YES NVRAM  administratively down down


Which is able to ping 10.7.1.0 and 10.1.1.100 just fine:

Code: 
ROUTER-3#ping 10.7.1.0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.7.1.0, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/36 ms

ROUTER-3#ping 10.1.1.100

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/40 ms


the-evaluator said:
It could just be that the router is dropping ICMP but is deliberately not responding to pings.
Click to expand...

The thing is though the 10.1.1.1 interface does respond to pings from the host, the problem is that the pings don't seem to be being routed to the second interface.
 
Last edited:
As BigT said 10.7.1.0 isn't an address you should be trying to use (it is a legal address, but it can cause you problems). Unless you fix that I think you're on a hiding to nothing.
 
My CCNA books all show that this setup is valid though, and I've seen this in production environments so surely there is some other problem that I should be looking for?

Sp00n said:
/31 is usable with subnet-zero enabled, making .0 and .1 usable addresses, http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13711-40.html

What do your routing tables look like?
Click to expand...

Ah I forgot about subnet zero, I'll take another look at this and post my routing tables after dinner. :D
 
Looks like subnet zero is enabled by default so that doesn't seem to be an issue.

The routing tables are as follows:

Router 1:

Code: 
ROUTER-1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 7 subnets, 3 masks
C        10.1.1.0/24 is directly connected, FastEthernet0/0
L        10.1.1.1/32 is directly connected, FastEthernet0/0
S        10.4.1.0/31 [1/0] via 10.7.1.1
C        10.5.1.0/31 is directly connected, FastEthernet0/1
L        10.5.1.0/32 is directly connected, FastEthernet0/1
C        10.7.1.0/31 is directly connected, Serial0/2/0
L        10.7.1.0/32 is directly connected, Serial0/2/0

Router 2:

Code: 
ROUTER-3#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
C       10.3.1.0/24 is directly connected, FastEthernet0/0
S       10.1.1.0/24 [1/0] via 10.7.1.0
C       10.7.1.0/31 is directly connected, Serial1/1
C       10.6.1.0/24 is directly connected, FastEthernet0/1
C       10.4.1.0/31 is directly connected, Serial1/0
 
I've actually just tried a tracert to 10.7.1.1 and the cmd prompt shows the first hop as 192.168.0.1 which is the default gateway of my other NIC, so it seems like instead of trying to use 10.1.1.1 to get to it it's actually using the wrong gateway! How can I get windows to use the default gateway of the other NIC as well?

EDIT - The ping is to 10.7.1.0 is now successful when I disable the other NIC. :)

Thanks guys. Just got to see if there is a way for windows to try both gateways rather than just using one.
 
Last edited:
Oh you didn't mention two networks. You can only have one default gateway, just add a static route for your lab network.

Fire up an elevated command prompt and type something like:
route add 10.0.0.0 mask 255.0.0.0 10.1.1.1 metric 30
 
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