Error with GtpUser on simulation multiMEC host

[edulchan]

I'm running a simulation a multiMEC scenario over a 40 s, but crush after few seconds 7-9s. The msg error show is:

A runtime error ocurred:

check_and_cast(): Cannot cast (inet::Indication*) ERROR to type 'inet::Packet*' -- in module (simu5g::GtpUser) MultiOperatorMultiMec.upf_A.gtp_user (id=217), at t=7.1020052264s, event #315291

Launch a debugger with the following command?
opp_ide omnetpp://dsp/debugger/attach?pid=55211

Attached the code file:

• omnetpp.ini
• .ned
• demo.xml
• .json

multiMec.zip

[josephinoo]

Hi @edulchan, I'm no expert on the subject, but I hope this helps.
The runtime error in simu5g::GtpUser is caused by an ICMP Destination Unreachable indication. This occurs because the UEs are attempting to communicate with their respective UALCMP nodes (e.g., for MEC application instantiation), but the routing configuration in demo.xml creates an ambiguity that the network stack cannot resolve.

In your omnetpp.ini, the UEs are configured to talk to the UALCMP:

• *.ue_A[*].app[0].ualcmpAddress = "ualcmp_A"
• *.ue_B[*].app[0].ualcmpAddress = "ualcmp_B"

When the simulation reaches the point where the WarningAlertApp starts its logic ( and onwards), the system tries to establish a control path. The crash at happens when the UPF receives a network error (as an inet::Indication) instead of a data packet, leading to the check_and_cast failure.

Step 1: Fix demo.xml Routing

The primary issue is the /8 netmask (255.0.0.0) used for cellular interfaces, which overlaps with the management subnet. You must use a stricter /16 mask and ensure the router is the gateway for inter-subnet traffic.

Replace the content of your demo.xml with this configuration:

<config>
    <interface hosts="gnb_A* ue_A* iUpf_A* upf_A" names="cellular" address="10.0.x.x" netmask="255.255.0.0"/>
    
    <interface hosts="gnb_B* ue_B* iUpf_B* upf_B" names="cellular" address="11.0.x.x" netmask="255.255.0.0"/>
    
    <interface hosts="router ualcmp_*" address="192.168.1.x" netmask="255.255.255.0"/>

    <wireless hosts="gnb_A* ue_A*" interfaces="cellular"/>
    <wireless hosts="gnb_B* ue_B*" interfaces="cellular"/>
    
    <interface hosts="**" address="192.168.2.x" netmask="255.255.255.0"/>
</config>

Step 2: Verify Gateway and Forwarding in omnetpp.ini

Ensure that all nodes acting as gateways have IP forwarding enabled so the ICMP error is not triggered. In your .ini, you already have:

• *.mecHost*.virtualisationInfrastructure.ipv4.forwarding = true
• *.ualcmp_A.gateway = "upf_A"

Ensure the router submodule also has forwarding enabled (it is true by default for inet.node.inet.Router, but you can force it):

*.router.ipv4.forwarding = true

By narrowing the netmask from 255.0.0.0 to 255.255.0.0, the Ipv4NetworkConfigurator will correctly identify that traffic from the 10.0.x.x network destined for the 192.168.1.x network (the UALCMP) must be routed through the upf_A and then the router. This prevents the "Destination Unreachable" error that crashes the GtpUser module.

[edulchan]

Now, show this error:

The line *.router.ipv4.forwarding = true, put in [General] section of omnetpp.ini