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Community Member

SG300 layer 3 routing question

A RV 180 is configured as follows:

VLAN 1 and 2 are configured. Inter-VLAN routing and device management is enabled on both VLANs.

The SVI for VLAN 1 is 192.168.1.1

The SVI for VLAN 2 is 192.168.2.1

A SG300 is configured as follows:

Layer 3 mode is enabled.

VLAN 1 and 2 are configured.

The SVI for VLAN 1 is 192.168.1.2

The SVI for VLAN 2 is 192.168.2.2

The SG300 and RV 180 are joined via a trunk link (1UP, 2T).

A host is connected to an access port (1UP) on the SG300 and configured with a static IP of 192.168.1.10.

I can connect to the SG300 device manager at http://192.168.2.2 from the host if the host's gateway is set to 192.168.1.2.

I cannot connect to the SG300 device manager at http://192.168.2.2 from the host if the host's gateway is set to 192.168.1.1. Why not?

I can ping 192.168.2.2 from the host whether the host's gateway is set to 192.168.1.1 or 192.168.1.2.

I can connect to WAN sites from the host (via the RV 180) whether the host's gateway is set to 192.168.1.1 or 192.168.1.2.

You are probably wondering why I don't just use 192.168.1.2 as my host's gateway address and call it a day. The reason is that I am trying to understand why I can't use the RV 180 to route traffic between the the SG300's subnets, as in router on a stick.

Note that I am using the device manager at 192.168.2.2 as a target in this example simply because it's already there. I actually ran into this problem while using a real host on a VLAN 2 access port, but I am leaving that out of this scenario to reduce the number of variables.

Thanks in advance for any insights!

9 REPLIES
Green

SG300 layer 3 routing question

Hi Robert, if I had to make a guess, I'd say the switch does not have a default gateway set.

config t

ip default-gateway 192.168.1.1

-Tom
Please mark answered for helpful posts

-Tom Please mark answered for helpful posts http://blogs.cisco.com/smallbusiness/
Community Member

SG300 layer 3 routing question

Thanks for the quick reply Tom!

The SG300 has a default route and it is set to the value you suggested. I know that the default route is properly set, because a host connected to the SG300 can reach the Internet via the RV180.

I found an even easier way to duplicate the problem:

Configure RV180 as follows:

  • Configure VLAN 1 and 2
  • Configure port 1 as (1UP, 2T)
  • Configure port 2 as (1UP)

Configure SG300 as follows:

  • Configure VLAN 1 and 2
  • Configure port 1 as (1UP, 2T)
  • Configure port 2 as (2UP)
  • Configure VLAN 2 SVI as 192.168.2.2

Connect the RV180 and SG300 using port 1 of each device.

Connect a host to port 2 on the RV180.

Connect a host to port 2 on the SG300.

You will be able to ping 192.168.2.2 from the host connected to the Rv180, but you won't be able to browse to http://192.168.2.2.

Similarly, you will be able to ping between the hosts, but you will not be able to make a TCP connection between the two hosts.

Can you try this and let me know if it works for you?

Community Member

SG300 layer 3 routing question

Hello,

While the SG300 is in Layer 3, can it act as a DHCP Server? If so, that might be causing some problems.

Alex

Community Member

SG300 layer 3 routing question

Yes, a SG300 that is running in Layer 3 mode can be configured to act as a DHCP server. I can't think of any reason why that would cause a problem though. I'll try disabling the DHCP server and see if it makes a difference.

Community Member

SG300 layer 3 routing question

I got it working using two different approaches.

My first approach was to replace the RV180 with a spare RV042 and see if I could get that combination working. I had to create a static route from the RV042 to the SG300, but once I did that everything worked as expected.

My next approach was to reset the RV180 to factory settings and disable VLAN support. I then created a static route from the RV180 to the SG300 and voila, it worked.

I made 3 configuration changes to the RV180 to make this work, and I'm not sure which of these changes did the trick: 1) I reset the RV180 to factory settings  2) I disabled VLAN support 3) I created a static route from the RV180 to the SG300.

Community Member

SG300 layer 3 routing question

Robert,

If I may ask, what is the main reason that the SG300 switch is in Layer 3 mode?

In Layer 3 mode, the switch is acting as a router, and that is why you can connect from one VLAN to the other.

If you do not need the switch to perform any routing then my recommendation is to turn it back to Layer 2 mode.

Because the Switch is in Layer 3 then it is considering itself as the default gateway for all the devices connected to it.

If you need assistance then do not hesitate to call us here at Cisco Small Business Support, 1-866-606-1866.

Richard Pruitt

Community Member

SG300 layer 3 routing question

Thanks for the suggestion Richard!

The reason I am running the SG300 in Layer 3 mode is because I want it, rather than the RV180, to do all the inter-VLAN routing in my network. I would guess that the SG300 can perform inter-VLAN routing much faster than a RV180, but I haven't tested that.

One thing I discovered when I disabled VLANs on the RV180 and added a static route from it to my SG300 is that the RV180 doesn't use the net mask that I specified when I added the static route. I used a net mask of 255.255.255.0, but it changed it added a route with a net mask of 255.255.254.0. I verfied that the 255.255.254.0 netmask is being used by pinging the next higher class C network and observed that the RV180 is forwarding the pings to the RV300, even though the higher numbered network is not defined there. I'll post the details in the router discussion later today.

Community Member

SG300 layer 3 routing question

Hello Robert,

Do you have the SG300 and the RV180W both working as DHCP servers at the same time? If so, this might be causing problems as hosts are trying to receiving address from both at once.

Let me know.

Thanks,

Alex

Community Member

SG300 layer 3 routing question

Hi Alex,

I have the RV180 enabled for DHCP on VLAN 1 and the SG300 enabled for DHCP on all other VLANs.

Thanks,

Bob

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