What is the gateway set to on

padelis.and.21 · ‎10-01-2016

So there is this simple GNS3 topology. The host is Ubuntu Linux tap0 interface.

ifconfig output:

tap0 Link encap:Ethernet HWaddr fe:6b:25:17:ab:af 
     inet addr:192.168.2.2 Bcast:192.168.2.255 Mask:255.255.255.0
     inet6 addr: fe80::fc6b:25ff:fe17:abaf/64 Scope:Link
     UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
     RX packets:995 errors:0 dropped:805 overruns:0 frame:0
     TX packets:69 errors:0 dropped:0 overruns:0 carrier:0
     collisions:0 txqueuelen:1000 
     RX bytes:98098 (98.0 KB) TX bytes:9562 (9.5 KB)

R1# show ip route:

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, FastEthernet0/1

R2# show ip route:

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0
R 192.168.2.0/24 [120/1] via 10.0.0.1, 00:00:04, FastEthernet0/0

When I ping from Host to R1 ( or R1 to Host ) its fine.

When I ping from R2 to R1 ( or R1 to R2 ) its fine.

When I ping from R2 to Host ( or Host to R2 ) all packets are lost.

The routing seems fine what is the problem here ?

cwhite0013 · ‎10-01-2016

What is the gateway set to on the Linux host? Should be able to see that with a "route -n". R2 knows how to reach the 192.168.2.0/24 subnet so it should be able to reach the host. I see a lot of drops on your tap0 interface. You can run an "ethtool -S tap0" and that should show you why the host is dropping the packets (possible duplex / speed mismatch?).

padelis.and.21 · ‎10-03-2016

Ooutput of ethtool -S tap0:

no stats available

Output of route -n:

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 146.176.231.254 0.0.0.0 UG 600 0 0 wlan2
1.1.1.1 146.176.231.254 255.255.255.255 UGH 600 0 0 wlan2
146.176.224.0 0.0.0.0 255.255.248.0 U 600 0 0 wlan2
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 wlan2
192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0

cwhite0013 · ‎10-03-2016

Ah yea, there's your issue. The default route on your server is pointing out of wlan2 and you don't have a route for the 10.0.0.0/24 network. This means that right now traffic destined to the 10.0.0.0/24 is being sent out your wlan2 interface rather than your tap0 interface.

On the server, create a static route for the 10.0.0.0/24 to route out your tap0 interface and your pings should be successful after that.

padelis.and.21 · ‎10-10-2016

I just did the whole thing in Windows. Thanks for the info though.

Router rip + GNS3