Cisco 3750-48PS switch cannot ping default gateway and internet

[MayurKenjale1992]

Hello All,

I need a assistance i resolving issues with my 48-port 3750 switch accessing internet.

Setup overview:

I have connected my switch to the ISP gateway-router (wireless). My ISP is Optimum Online where they provide a modem followed by a gateway-router behind it. My switch, as mentioned, sits behind the gateway-router connected on one of the LAN ports to switch's Fa2/0/1 interface.

I have configured default VLAN1 with IP address 192.168.1.20 255.255.255.0. The Fa2/0/1 to which gateway-router is connected is configured as trunk port.

ip routing command has been configured

ip default-gateway 192.168.1.1 was also configured

**Both the above commands were put in and removed as trial-and-error**

ports are all no shutdown (they are active).

Issue:

When i console into the switch, I can ping default gatway IP of 192.168.1.1 but cannot ping 8.8.8.8

When i remove the console connection and telnet into the switch (on IP: 192.168.1.20), I cannot even ping default gateway IP nor i can ping the internet.

Please advise resolution to this issue.

[marce1000]

 - OK, but 'ip default-gateway' usually applies locally to the switch. The intend is to provide internet connectivity for connected hosts. Notice the difference between 'ip default-gateway' and setting up full ip routing which according to me you must try to accomplish. Then usually a subnet is created between a local routed port on the switch and the ISP. You then route local traffic to the  local routed port :

   https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/77805-troubleshoot-3750.html#anc8

 M.

[MayurKenjale1992]

Thanks for your input. I am aware of the ip default gateway / ip routing concept, however, I had to do some kind of trial and error here as nothing according to the normal concept and steps worked. This, if we see is a very simple scenario, but things are not working out the way they should.

[Reza Sharifi]

Hi,

Since you are only using one vlan (vlan1) between the 3750 and the ISP gateway router, you don't need a trunk port, you just need an access port on fa2/0/1. Also, since the 3750 switch is just layer-2, all you need is a default-gateway. Your end devices gateway should be the ISP gateway router IP (192.168.1.1)

HTH 

[MayurKenjale1992]

Thank you for your input. You are right. However, access port did not work is why I tried using it as a trunk. I tried all possible ways to narrow it down. As I said in my earlier, the concept is very simple here and the setup but i am not finding a reason where things are going wrong.

[Richard Burts]

I believe that the crux of the issue is this from the original post "ip routing command has been configured". There is certainly reason to question whether this is needed. But in the current environment it is configured and that has some implications.

In particular the ip default-gateway command in intended to be used on layer 2 switches that do not have ip routing enabled. On a switch where ip routing is enabled the default-gateway command is ignored. To fix this issue the original poster must either leave ip routing in place and configure a static default route (something like ip route 0.0.0.0 0.0.0.0 192.168.1.1) or they must remove the ip routing command.

Based on the fact that all ports of the switch are in the default vlan 1, I would suggest that 

- there is no need (and no benefit) from having ip routing enabled.

- there is no need (and no benefit) from configuring the connection from the switch to the ISP as a trunk.

It is not clear whether devices connected to this switch will get IP addresses using DHCP from the ISP router, or get IP addresses using DHCP from something else, or will have IP addresses hard coded. But for any of the choices other than DHCP from ISP make sure that the DHCP defines the default router as 192.168.1.1.

[MayurKenjale1992]

I understand that. However, none of the usual ways to make this work were working. I tried my best with all possible ways tweaking the same.

[Richard Burts]

You have told us multiple times that you have tried lots of trial and error but that it still is not working. We do not have much detail to work with to understand this issue. Can we take the next step in trying to understand the issue by posting the running config of the switch? It would also be helpful if you would post the output of show ip route and of show arp.