Zyxel GS1200-5HP v2 does not forward traffic within the same VLAN

jtk
jtk Posts: 25 image  Freshman Member
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in Switch
Kuvakaappaus 2025-09-12 20-40-40.png

I have the VLAN configuration above (for ports 03 and 04 there are no other active VLANs). For some reason the switch does not forward packets between ports 03 and 04, but traffic to port 05 (the trunk port towards the firewall/router with the gateway ip of the VLAN) works.

Any ideas on how to allow traffic within the same VLAN on the switch?

There is no link aggregation used.

Accepted Solution

  • Zyxel_Melen
    Zyxel_Melen Posts: 3,916 image  Guru Member
    Zyxel Certified Network Engineer Level 1 - Switch Zyxel Certified Network Administrator - Switch Zyxel Certified Network Administrator - Nebula Zyxel Certified Sales Associate
    edited September 15 Answer ✓

    Hi @jtk

    It seems like you have enabled Port Isolation.

    image.png

    Could you check the setting in the page Port > Advanced Settings?

    Zyxel Melen


All Replies

  • PeterUK
    PeterUK Posts: 4,099 image  Guru Member
    250 Answers 2500 Comments Friend Collector Eighth Anniversary

    Maybe the devices on ports 3 and 4 have a firewall

  • jtk
    jtk Posts: 25 image  Freshman Member
    First Comment Friend Collector First Anniversary

    No. I can ssh both of them from a different VLAN, while connection comes from the router via the trunk port 5. But I cannot ssh, ping or anything from each other.

  • PeterUK
    PeterUK Posts: 4,099 image  Guru Member
    250 Answers 2500 Comments Friend Collector Eighth Anniversary
    edited September 13

    Can you Wireshark on one device then ping from the other device to the one doing the Wireshark with filter

    icmp or arp

    You should see a broadcast ARP with who has IP seen by any the one running the Wireshark and IP of that is as this MAC in reply

    The other reason could be that one or both devices use subnet 255.255.255.255

  • Zyxel_Melen
    Zyxel_Melen Posts: 3,916 image  Guru Member
    Zyxel Certified Network Engineer Level 1 - Switch Zyxel Certified Network Administrator - Switch Zyxel Certified Network Administrator - Nebula Zyxel Certified Sales Associate
    edited September 15 Answer ✓

    Hi @jtk

    It seems like you have enabled Port Isolation.

    image.png

    Could you check the setting in the page Port > Advanced Settings?

    Zyxel Melen


  • jtk
    jtk Posts: 25 image  Freshman Member
    First Comment Friend Collector First Anniversary

    This was it! Thank you. For some reason it was very difficult for me to find the setting even after you pointed that out.

    Thank you for both of you for helping out!

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