Can't ping wan Gateway from directly connected Cisco 4431

[ganeshccie]

Cisco 4431 router gi 0/0/0 interface is connected to broadband router and is configured to get IP address from DHCP. Broadband router is DHCP server. Negotiation auto and ip nat outside is configured.

I can see 192.168.1.7 ip is assigned to Gi0/0/0 interface under sh ip inter brief command.

Ip route 0.0.0.0 0.0.0.0 Gi0/0/0 DHCP  is configured.

Now when I try to ping 192.168.1.1 which is a gateway...I can ping.

But after sometime I can't ping the gateway.

Now I checked the arp and can see the arp entry for gateway. Arp time out is default 4 hours.

Now if I bounce the interface, I can ping the gateway but again after sometime I can't ping the gateway.

This Cisco 4431 router newly installed in place of Cisco 2960x. 2960x was working fine.

Just unable to understand what going wrong.

[MHM Cisco World]

Show arp when you can ping and can not 

Please share here 

[ganeshccie]

When I can't ping the gateway arp is as below,

Interrnet. 192.168.1.1. 0. 495d.3623.fa78. ARPA. Gi 0/0/0

When ping works, arp is as below,

Internet. 192.168.1.1.  0.  485d.3623.fa78.  ARPA. Gi 0/0/0

Sorry I can't past the output due to security reasons so I have verified the output and typed it here.

[ganeshccie]

Just noticed a typo mistake in first arp....please read Mac address as 485d.3623.fa78

[MHM Cisco World]

Ping 192.168.1.255

Ping above and see which IP will reply.

[ganeshccie]

Ping does not work to 192.168.1.255 but I can ping 192.168.1.1

Just waiting for the issue to start again. 

No entry for .255 in arp table

[MHM Cisco World]

This called broadcast ping 

We need to see if ISP have same IP or not.

[ganeshccie]

Yes I know it's a broadcast IP.

But I think it doesn't matter what is the broadcast IP, since we have configured interface to get IP address from DHCP and no subnet mask manually configured.

If we would have configured ip address statically, then there are chances that subnet mask may be different at ISP side and at 4431 end.

[ganeshccie]

Just checked under sh interface gi 0/0/0 command and found internet address as 192.168.1.7/24

So technically 192.168.1.255 is a broadcast IP

But unfortunately I am unable to ping this broadcast ip

[ganeshccie]

Tried to ping 255.255.255.255, received reply from all BDI interfaces except from Gi 0/0/0 or 192.168.1.0/24 subnet