gw-tester

GW Tester

A pseudo eNB and MME as a tester for S/P-GW.

What's this?

It is a burden to use actual UE/eNB/MME just to test S/P-GW, isn't it?
GW Tester emulates the minimal required behavior of surrounding nodes to perform quick and simple testing on S/P-GW.

A blog post by the author is available here for those who are interested in :)
NOTE: Some of the blog post's configurations or codes might be no longer relevant in the current version.

How it works

Authentication

Nothing!
Subscribers defined in the enb.yml file can immediately attach and use the created sessions. MME accepts any subscribers without an authentication procedure. Communication over the S1-MME interface is done with protobuf/gRPC instead of the S1AP protocol.

=== AD ===
Looking for a Go package for LTE authentication?
MILENAGE algorithm implementation is available :)

https://github.com/wmnsk/milenage

Gateway Selection

No DNS lookup by TAI/APN is implemented. MME just chooses gateways according to the mapping of source IP ranges and GW's IPs defined in mme.yml. This behavior might be changed in the future.

Session Establishment

MME exchanges the real GTPv2 session establishment messages like Create/Modify/Delete Session with S-GW.

• IP address assignment
  Currently, we use the IP address that is defined in enb.yml, and the one passed by P-GW is ignored. This behavior might be changed in the future to be more practical.

• TEID allocation
  It can be both static and dynamic. Random TEID will be allocated by enb if i_tei in enb.yml is set to 0. For outgoing TEID, the one that S-GW allocates will be used.

U-Plane Data Injection

eNB forwards incoming traffic from UE or generates traffic by itself depending on the type in enb.yml. GTP-U feature is based on Linux Kernel GTP-U with netlink.

type	behavior
external	eNB encapsulates and forwards the incoming packets from src_ip toward the specified interface(euu_if_name).
http_get	eNB starts sending HTTP GET to the specified URL.
...	(other types might be implemented in the future!)

Getting Started

Prerequisites

• Linux (kernel >= 4.12) with root privilege
• net.ip_forward enabled
• ports opened: 36412/TCP, 2123/UDP, 2152/UDP

Run testers

Just go get eNB and MME. Functional S-GW and P-GW are also available in the same directory if you need them.

go get github.com/wmnsk/go-gtp/examples/gw-tester/enb
go get github.com/wmnsk/go-gtp/examples/gw-tester/mme

And run them with YAML configuration. See Configuration section for details.

./mme

./enb

Then you'll see;

• MME starts sending GTPv2 Create Session Request to S-GW after it receives subscriber information from eNB.
• When sessions are successfully created on S/P-GW, eNB sets up GTP-U tunnels with S-GW.

After the successful creation of the sessions, you can inject packets externally or generate them on eNB.

Configurations

Each node has a YAML file as a configuration.
In general, config consists of the network information of local/remote nodes and some node-specific parameters.

eNB

Global

These values are used to identify eNB. Some of them are just to be set inside the packets and not validated.

config	type of value	description
mcc	string	MCC of eNB
mnc	string	MNC of eNB
rat_type	uint8	RAT Type (6 for E-UTRAN)
tai	uint16	TAI of eNB
eci	uint32	ECI of eNB
mme_addr	string	IP/Port of MME to dial, for S1-MME interface
use_kernel_gtp	bool	Use Kernel GTP or not. U-Plane does not work when set to false.
prom_addr	string	IP/Port of MME to serve Prometheus

Local Addresses

local_addresses are the IP addresses/ports to be bound on the local machine.

config	type of value	description
s1c_ip	string	local IP for S1-MME interface
s1u_ip	string	local IP for S1-U interface

Subscribers

subscribers are the list of subscribers to attach.

config	type of value	description
imsi	string	IMSI of the subscriber
msisdn	string	MSISDN of the subscriber
imeisv	string	IMEISV of the subscriber
src_ip	string	source IP of the subscriber (not assigned by P-GW)
i_tei	uint32	incoming TEID that S-GW should specify the subscriber
type	string	external or http_get. see U-Plane Data Injection
euu_if_name	string	name of the network interface on eUu side. type=external: Used to receive traffic from external UE type=http_get: Used as a source interface that src_ip is added
http_url	string	URL to HTTP GET by built-in traffic generator
reattach_on_reload	bool	whether to perform the attach procedure again on config reload

MME

Global

These values are used to identify MME. Some of them are just to be set inside the packets and not validated.

config	type of value	description
mcc	string	MCC of MME
mnc	string	MNC of MME
apn	string	APN assigned to all the subscriber
prom_addr	string	IP/Port of MME to serve Prometheus

Local Addresses

local_addresses are the IP addresses/ports to be bound on the local machine.

config	type of value	description
s1c_addr	string	local IP/Port for S1-MME interface
s11_ip	string	local IP for S11 interface

Gateway IPs

IP addresses required to know/tell S-GW. This is typically done by DNS lookup with APN, but it's static for now.

config	type of value	description
sgw_s11_ip	string	S-GW's IP for S11 interface
pgw_s5c_ip	string	P-GW's IP for S5-C interface

S-GW

Local Addresses

local_addresses are the IP addresses/ports to be bound on the local machine.

config	type of value	description
s11_ip	string	local IP for S11 interface
s1u_ip	string	local IP for S1-U interface
s5c_ip	string	local IP for S5-C interface
s5u_ip	string	local IP for S5-U interface
use_kernel_gtp	bool	Use Kernel GTP or not.
prom_addr	string	IP/Port of S-GW to serve Prometheus

P-GW

Global

config	type of value	description
sgi_if_name	string	name of the network interface on SGi side. Used to downlink route traffic.
route_subnet	string	IP subnet of UEs that should be routed properly.
use_kernel_gtp	bool	Use Kernel GTP or not. U-Plane does not work when set to false.
prom_addr	string	IP/Port of P-GW to serve Prometheus

Local Addresses

local_addresses are the IP addresses/ports to be bound on the local machine.

config	type of value	description
s5c_ip	string	local IP for S5-C interface
s5u_ip	string	local IP for S5-U interface
sgi_ip	string	local IP for SGi interface

Other Features

Reloading config

The programs can handle SIGHUP to reload config without deleting sessions. Update YAML file and send SIGHUP to the process.

Instrumentation

GW Tester nodes expose some metrics for Prometheus if prom_addr is given in each config. You can see the sample response from each node in this Gist.
I'm planning to add some more metrics like "success rate of HTTP probe", etc.

Metrics	Name	Description
Active sessions	<node-name>_active_sessions	number of session established currently
Active bearers	<node-name>_active_bearers	number of GTP-U tunnels established currently
Messages sent	<node-name>_messages_sent_total	number of messages sent by messagge type
Messages received	<node-name>_messages_received_total	number of messages received by messagge type