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manual: explain GTP Echo workaround for tunmap

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Change-Id: Ic824fc876d1fad181254cb6894e51464c443b53c
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Neels Janosch Hofmeyr
2024-01-24 02:57:32 +01:00
parent 8ec1871914
commit 60cbef5885
1 changed files with 53 additions and 7 deletions
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doc/manuals/chapters/running.adoc
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@@ -99,10 +99,10 @@ include::upf_gtp_roles.dot[]
GTP kernel module configuration in the `tunend` section can be omitted for sites
that serve only as GTP forwarding proxy, without encapsulation/decapsulation of
GTP payloads.
GTP payloads -- except to provide GTP Echo service, see <<gtp_echo>>.
Likewise, netfilter configuration in the `tunmap` section can be omitted for
sites only serving as GTP tunnel endpoint.
Netfilter configuration in the `tunmap` section can be omitted for sites only
serving as GTP tunnel endpoint.
[[gtp_module]]
=== Configure Linux Kernel GTP Module for `tunend`
@@ -167,11 +167,57 @@ this GTP device. When using ANY, there should be exactly one GTP dev configured.
The Linux kernel netfilter module is used for GTP tunnel proxying, also known as
tunnel forwarding or tunnel mapping.
Using the netfilter module usually requires no configuration in `osmo-upf.cfg`.
When using the netfilter module, you may set up `osmo-upf.cfg` for:
- GTP Echo (required)
- nft table name (optional)
`osmo-upf` creates a new netfilter table, under which it submits rule sets for
GTP tunnel proxying. This table name defaults to `osmo-upf`. A custom table name
can be configured in `osmo-upf.cfg` like this:
[[gtp_echo]]
==== GTP Echo
You need to ensure that OsmoUPF responds to GTP Echo requests.
- A GTP device configured for `tunend` implicitly includes a GTP Echo service.
- For `tunmap`, no GTP Echo mechanism is implemented.
So, when your use case is `tunmap` only, you should still add a GTP device as
for `tunend`, only to provide the GTP Echo service.
Here are some options to do so:
If you have no GTP devices configured in `osmo-upf.cfg` yet, you can add a
single GTP device without a specific IP address, in order to respond to GTP-U
Echo requests on all interfaces to anyone that is asking:
----
tunend
dev create gtp-echo
----
Note that `gtp-echo` is just an arbitrary GTP device name, choose any string
that makes a valid network device name and is still available, as in the `dev`
argument in the `ip addr show dev` command on Linux.
This will bind osmo-upf on 0.0.0.0:2152 to respond to GTP Echo requests.
If you would like to limit GTP Echo responses to specific network interfaces,
you need to add a separate GTP device per local IP address:
----
tunend
dev create gtp-echo1 192.168.0.23
dev create gtp-echo2 10.9.8.17
----
This will bind osmo-upf only on 192.168.0.23:2152 and 10.9.8.17:2152 to respond
to GTP Echo requests.
For creating and manipulating a GTP device in more versatile ways, see
<<gtp_module>>.
==== nft Table Name
For `tunmap`, `osmo-upf` creates a new nft table, under which it submits
rule sets for GTP tunnel proxying. This table name defaults to `osmo-upf`. A
custom table name can be configured in `osmo-upf.cfg` like this:
----
tunmap