ARP Broadcasts in STP taking a switch down GNS3

[Mantas Sti]

Hello.

Got a simple STP instance with 3 L2 switches in GNS3.

Just Spanning tree priorities and VLAN 1 interfaces are configured:

SW-01#sh run | i spanning
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 4096

SW-01#sh run int vlan 1
interface Vlan1
ip address 192.168.1.1 255.255.255.0
end

SW-02#sh run | i spanning
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 8192

SW-02#sh run int vlan 1
interface Vlan1
ip address 192.168.1.2 255.255.255.0
end

SW-03#sh run | i spanning
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 12288

SW-03#sh run int vlan 1
interface Vlan1
ip address 192.168.1.3 255.255.255.0
end

After starting GNS3, endless ARP broadcasts start between SW-01 and SW-02 (Wireshark screenshot). It gradually increases VM CPU usage to 99% and eventually takes SW-02 down.

When checking ip arp on SW-02 I can see that it has ARP entries for all 3 switches, but I cannot ping SW-01 or SW-03.

This happens every time I start this topology and only SW-02 goes down. All interfaces are trunk and all VLANs are allowed.

Tried replacing the switch with another switch but he same happens.

Images tried:

i86bi-linux-l2-ipbasek9-15.1g.bin
i86bi-linux-l2-adventerprisek9-15.1a.bin

If I take the link between SW-01 and SW-02 there are no endless ARP broadcasts but there's no more redundancy.

Attached the supporting screenshots.

Did anyone come this across and if yes how to fix it please?

[luis_cordova]

Hi @Mantas Sti ,

I have always heard that GNS3 has problems with switching.

Have you tried performing this laboratory in another simulator?

For example, you can try PacketTracer or EVE.

This is to rule out that it is a simulator problem.

Regards

[Mantas Sti]

@luis_cordova, @Martin L 

Thanks for your replies guys.

The trunking encapsulation I use is dot1q. I'm using SVIs for pinging and telnet purposes.

Changed the VLAN to VLAN 10 and I'm not getting endless ARP Broadcasts any more. Pinging works as normal and all switches have ARP entries for every other switch.

It might be an issue with using VLAN 1 for STP.

This is now resolved. Thanks for your replies.

[Martin L · Accepted solution]

it is likely gns3 problem with your images.

0. what type of trunks do u have ? do2.1q or ISL. ? auto negotiated or manually set ?
1. set IP to ARP manually if u can
2. do not use vlan 1, change interface vlan 1 to vlan 10
3. do not use SVIs at all ; use routers as end hosts