manual: use 'tunend' and 'tunmap'

Change-Id: I09a2fa28465945c98b58b4093c7d5de65e184645

doc/manuals/chapters/overview.adoc

@@ -79,14 +79,14 @@ and encapsulation/decapsulation of GTP tunnels.
 OsmoUPF does not support the complete PFCP feature set. It detects exactly two
 use cases that will provide service of actual GTP tunnels:
 
-* GTP tunnel encapsulation/decapsulation:
+* `tunend`: GTP tunnel encapsulation/decapsulation:
   - One Packet Detection Rule (PDR) accepts a GTP tunnel from the Access side
     with an Outer Header Removal.
   - This PDR uses a Forwarding Action Rule (FAR) for plain IP towards Core.
   - Another PDR accepts plain IP on a specific IP address from Core.
   - The second PDR uses a FAR towards Access with Outer Header Creation for GTP.
 
-* GTP tunnel forwarding:
+* `tunmap`: GTP tunnel forwarding:
   - One Packet Detection Rule (PDR) accepts a GTP tunnel from the Access side
     with an Outer Header Removal.
   - This PDR uses a Forwarding Action Rule (FAR) towards Core with an Outer

doc/manuals/chapters/running.adoc

@@ -55,7 +55,7 @@ If multiple `osmo-upf` processes are running on the same Linux kernel, each
 naming of individual tunnel rulesets does not collide:
 
 ----
-nft
+tunmap
  table-name osmo-upf-2
 ----
 
@@ -103,10 +103,10 @@ GTP kernel module configuration can be omitted for sites that serve only as GTP
 forwarding proxy, without encapsulation/decapsulation of GTP payloads.
 
 [[gtp_module]]
-===== Configure Linux Kernel GTP Module
+===== Configure Linux Kernel GTP Module for `tunend`
 
-The Linux kernel GTP module is used for GTP encapsulation/decapsulation from/to
-"the internet".
+The Linux kernel GTP module is used for the `tunend` use case, i.e. GTP
+encapsulation/decapsulation from/to "the internet".
 
 To use the GTP kernel module, OsmoUPF requires a GTP device, which is a
 dedicated network device provided by the Linux kernel, serving as GTP tunnel
@@ -120,7 +120,7 @@ The following configuration placed in `osmo-upf.cfg` creates a GTP device called
 `apn23` on startup, which is also destroyed on program exit:
 
 ----
-gtp
+tunend
  dev create apn23
 ----
 
@@ -131,7 +131,7 @@ The following configuration placed in `osmo-upf.cfg` uses a pre-existing device
 called `apn42`:
 
 ----
-gtp
+tunend
  dev use apn42
 ----
 
@@ -153,7 +153,7 @@ Instance IE passed in the PFCP Session messages (PDR/FAR). Until then, it makes
 little sense to configure more than one GTP device.
 
 [[nftables]]
-===== Configure Linux netfilter
+===== Configure Linux netfilter for `tunmap`
 
 The Linux kernel netfilter module is used for GTP tunnel proxying, also known as
 tunnel forwarding or tunnel mapping.
@@ -165,6 +165,9 @@ GTP tunnel proxying. This table name defaults to `osmo-upf`. A custom table name
 can be configured in `osmo-upf.cfg` like this:
 
 ----
-nft
+tunmap
  table-name my-table-name
 ----
+
+When running more than one osmo-upf process on a system, pick distinct table
+names to avoid name collisions in the nftables reulesets.