Network is unreachable error for GTP interface

[avatli]

Hi

I'm trying to build a setup by using GTP module and libgtpnl tools on  
Centos 7 but I haven't been successful yet. Worse, I don't know how to  
debug the problem. I also stopped firewall and iptables.

How can I debug/solve, I will be very glad if you help. dmesg or  
system messages show show nothing. Why is GTP interface (link) is  
unreachable.

Thanks in advance

- Volkan


$ modinfo gtp
filename:        
/lib/modules/5.7.7-1.el7.elrepo.x86_64/kernel/drivers/net/gtp.ko
alias:          net-pf-16-proto-16-family-gtp
alias:          rtnl-link-gtp
description:    Interface driver for GTP encapsulated traffic
author:         Harald Welte <hwe...@sysmocom.de>
license:        GPL
srcversion:     191407DA5399304D93D62C7
depends:        udp_tunnel
retpoline:      Y
intree:         Y
name:           gtp
vermagic:       5.7.7-1.el7.elrepo.x86_64 SMP mod_unload modversions

$ modinfo udp_tunnel
filename:        
/lib/modules/5.7.7-1.el7.elrepo.x86_64/kernel/net/ipv4/udp_tunnel.ko
license:        GPL
srcversion:     0A315BA6124B0664F4D23FB
depends:
retpoline:      Y
intree:         Y
name:           udp_tunnel
vermagic:       5.7.7-1.el7.elrepo.x86_64 SMP mod_unload modversions

$ ip addr add 172.0.0.1/24 dev enp9s0
$ ip addr add 172.99.0.1/32 dev lo

$ ./gtp-link add gtp1
WARNING: attaching dummy socket descriptors. Keep this process running  
for testing purposes.

$ ./gtp-tunnel add gtp1 v1 200 100 172.99.0.2 172.0.0.2
$ ip route add 172.99.0.2/32 dev gtp1

$ ./gtp-tunnel list
version 1 tei 200/100 ms_addr 172.99.0.2 sgsn_addr 172.0.0.2

$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN  
group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet 172.99.0.1/32 scope global lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
7: enp9s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state  
UP group default qlen 1000
    link/ether 08:35:71:ab:54:5f brd ff:ff:ff:ff:ff:ff
    inet 172.0.0.1/24 scope global enp9s0
       valid_lft forever preferred_lft forever
8: gtp1: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 0 qdisc noqueue  
state UNKNOWN group default qlen 1000
    link/none

$ ip route
default via 192.168.1.1 dev enp2s0 proto static metric 100
172.0.0.0/24 dev enp9s0 proto kernel scope link src 172.0.0.1
172.99.0.2 dev gtp1 scope link

$ ping 172.99.0.2
PING 172.99.0.2 (172.99.0.2) 56(84) bytes of data.
ping: sendmsg: Network is unreachable
ping: sendmsg: Network is unreachable
ping: sendmsg: Network is unreachable