Cellular Network Infrastructure » osmo-ePDG - VoWifi Evolved Packet Data Gateway

The file comes from open5gs.git ./configs/systemd/99-open5gs.network:

[Match]
Name=ogstun

[Network]
Address=10.45.0.1/16
Address=2001:db8:cafe::1/48

[Link]
MTUBytes=1400
RequiredForOnline=false

At the same time, configs/open5gs/upf.yaml.in has:

  session:
    - subnet: 10.45.0.1/16
    - subnet: 2001:db8:cafe::1/48

https://www.freedesktop.org/software/systemd/man/latest/systemd.network.html seems to have a "[Route]" option which could be used instead.

So this looks wrong. I'll do some tests to see if I can get something working with this and then submit a patch to open5gs upstream.

lynxis applied the proposed open5gs-upfd patch installing the new file for systemd-network in ansible-prototype.git 73398e548a6657d100fa371309422eb68f051545 until the discussions upstream are clarified/agreed upon what's needed.

After change [1], open5gs should in theory properly identify difference between the subnet/pool of addresses and the local IP address set on the tundev, by means of "subnet" vs "gateway" fields in the config.

Since our config right now is:

roles/epc/defaults/main.yml
7:epc_ue_network: 10.45.0.0/16

roles/epc/templates/smf.yaml
37:    - subnet: {{ epc_ue_network }}

roles/epc/templates/upf.yaml
21:    - subnet: {{ epc_ue_network }}

Then we are properly defining in config file that we are not using an IP address for the gateway and hence .1 can be allocated for an UE.

However, open5gs maintainer mentioned he wants to keep assigning an IP address (.1) to the tundev in default setup, which means the default config is now (note the extra "gateway" field):

    - subnet: 10.45.0.0/16
      gateway: 10.45.0.1

Similarly, the default systemd file still contains code to set the IP address on the tundev (./configs/systemd/99-open5gs.network):

[Network]
Address=10.45.0.1/16
Address=2001:db8:cafe::1/48

So our patch is still needed to avoid setting the IP address on the tundev.

It may make sense to update our upstream PR to include the explicit network routing rules, so removing the IP address is just a matter of commenting out the 2 "Address=" lines. Right now, if one does that with default systemd file, routing will be broken since the IP address are the one setting the implicit routing when they are added.

lynxis we can also simplify our setup by using open5gs default setup, where we let systemd add the IP address and we use something like the following in our open5gs (you must use current open5gs main!):

    - subnet: 10.45.0.0/16
      gateway: 10.45.0.1

[1] https://github.com/open5gs/open5gs/commit/a6830b30a0093ed2fa9d563445bf67026588a8f2