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SG300 default vlan setup blocking traffic

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  • SG300 default vlan setup blocking traffic

    I have 4 Cisco SG300 series switches running in their DEFAULT configuration. The network was a single /24 subnet. I tried expanding this subnet to a /23.
    Original subnet -
    New subnet

    I don't think I need to setup VLans in the switches because I don't have multiple Vlans and would prefer to just keep using the default Vlan.

    But I'm having trouble talking between the .31.x devices and the .30.x devices. Traffic is mostly dropped. It will ping once or twice then stop.

    When communication goes down if I view the arp -a on a PC that's having trouble communicating it shows a single Cisco brand MAC for all the devices in the new part of the subnet that it's unable to ping.

    Also I tried swapping these Cisco switches with a single dumb switch and communication worked just fine. I thought the default config for these switches would perform just like a dumb switch (but I guess not).

    I'm sure there's a simple setup on these SG300's that will allow this but I'm not very familiar with their config utility. I am familiar with Cisco IOS but these gui based devices or very different.

  • #2
    Re: SG300 default vlan setup blocking traffic

    If you addressing is correct on all devices for the /23 then they should be able to arp directly for each other. If your seeing the management interface in the arp cache on the hosts then that tells me its trying to route and not switch the traffic. I would look at the addressing again. Im not familiar with the cisco small business line of switches.
    CCNA, CCNA-Security, CCNP
    CCIE Security (In Progress)


    • #3
      Re: SG300 default vlan setup blocking traffic

      Thanks for the input. The arp cache did show a Cisco branded mac but it turns out it was the mac of a Cisco router at another company which is connected via fiber to one of our switch ports. Apparently their router was responding to traffic destined for the new part of my /23 subnet. I'll work it out with them tomorrow. Thanks