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#1 2023-01-11 11:01:26

krnlpnc
Member
Registered: 2023-01-11
Posts: 6

[Solved] Networking issues with T-Mobile modems

Hi!

Ever since I got a modem from my new internet provider (T-Mobile/Magenta) I've been having weird networking issues. I've never had any problems connecting to any WiFi AP with my laptop in the last 10 years, but this one just causes strange issues.
The connection works flawlessly for a couple of seconds, then there is complete packet loss, then it works again. See, for example, the output of ping:

PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=2 ttl=118 time=18.1 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=118 time=17.7 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=118 time=22.7 ms
64 bytes from 8.8.8.8: icmp_seq=5 ttl=118 time=21.4 ms
64 bytes from 8.8.8.8: icmp_seq=6 ttl=118 time=19.7 ms
64 bytes from 8.8.8.8: icmp_seq=7 ttl=118 time=17.3 ms
64 bytes from 8.8.8.8: icmp_seq=8 ttl=118 time=18.2 ms
64 bytes from 8.8.8.8: icmp_seq=9 ttl=118 time=18.0 ms
64 bytes from 8.8.8.8: icmp_seq=58 ttl=118 time=2109 ms
64 bytes from 8.8.8.8: icmp_seq=59 ttl=118 time=1096 ms
64 bytes from 8.8.8.8: icmp_seq=60 ttl=118 time=82.3 ms
64 bytes from 8.8.8.8: icmp_seq=61 ttl=118 time=18.5 ms
64 bytes from 8.8.8.8: icmp_seq=62 ttl=118 time=18.1 ms
64 bytes from 8.8.8.8: icmp_seq=63 ttl=118 time=20.2 ms
64 bytes from 8.8.8.8: icmp_seq=64 ttl=118 time=19.0 ms
64 bytes from 8.8.8.8: icmp_seq=65 ttl=118 time=19.2 ms
64 bytes from 8.8.8.8: icmp_seq=66 ttl=118 time=25.9 ms
64 bytes from 8.8.8.8: icmp_seq=67 ttl=118 time=17.9 ms
64 bytes from 8.8.8.8: icmp_seq=68 ttl=118 time=18.4 ms
64 bytes from 8.8.8.8: icmp_seq=105 ttl=118 time=1951 ms
64 bytes from 8.8.8.8: icmp_seq=106 ttl=118 time=938 ms
64 bytes from 8.8.8.8: icmp_seq=107 ttl=118 time=18.2 ms
64 bytes from 8.8.8.8: icmp_seq=108 ttl=118 time=18.6 ms
64 bytes from 8.8.8.8: icmp_seq=109 ttl=118 time=19.1 ms
64 bytes from 8.8.8.8: icmp_seq=110 ttl=118 time=18.9 ms
64 bytes from 8.8.8.8: icmp_seq=111 ttl=118 time=19.3 ms
64 bytes from 8.8.8.8: icmp_seq=112 ttl=118 time=47.9 ms
64 bytes from 8.8.8.8: icmp_seq=113 ttl=118 time=19.6 ms
64 bytes from 8.8.8.8: icmp_seq=114 ttl=118 time=18.9 ms
64 bytes from 8.8.8.8: icmp_seq=145 ttl=118 time=990 ms
64 bytes from 8.8.8.8: icmp_seq=146 ttl=118 time=17.8 ms
64 bytes from 8.8.8.8: icmp_seq=147 ttl=118 time=19.4 ms
64 bytes from 8.8.8.8: icmp_seq=148 ttl=118 time=19.0 ms
64 bytes from 8.8.8.8: icmp_seq=149 ttl=118 time=19.9 ms
^C
--- 8.8.8.8 ping statistics ---
149 packets transmitted, 34 received, 77.1812% packet loss, time 149609ms
rtt min/avg/max/mdev = 17.305/227.435/2108.949/530.695 ms, pipe 3

DNS resolution is also having some issues:

> dig google.com
;; communications error to 192.168.0.1#53: connection refused
;; communications error to 192.168.0.1#53: connection refused
;; communications error to 192.168.0.1#53: connection refused
;; communications error to 2a02:8383:d:c::1000#53: timed out

; <<>> DiG 9.18.10 <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31765
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;google.com.			IN	A

;; ANSWER SECTION:
google.com.		90	IN	A	142.251.37.14

;; Query time: 13 msec
;; SERVER: 2a02:8383:d:c::1#53(2a02:8383:d:c::1) (UDP)
;; WHEN: Wed Jan 11 11:34:38 CET 2023
;; MSG SIZE  rcvd: 55

Everything works fine on all Android phones connected to the modem. I've exchanged the original "Magenta Fiber Box 2" modem with the older "Magenta Fiber Box" as the newer one has very limited configuration options. After the exchange the same problems started to appear on my girlfriend's Fedora laptop.

I'm quite lost as to why this is happening. Any help is greatly appreciated, thank you!

Last edited by krnlpnc (2023-01-14 09:43:05)

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#2 2023-01-11 17:07:55

-thc
Member
Registered: 2017-03-15
Posts: 533

Re: [Solved] Networking issues with T-Mobile modems

Please try connecting to one of the LAN ports of the "Fiber Box" (if available on your arch machine).
If this works, it's purely WiFi related.

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#3 2023-01-11 18:11:05

krnlpnc
Member
Registered: 2023-01-11
Posts: 6

Re: [Solved] Networking issues with T-Mobile modems

Sorry, I forgot to mention that. Using a wired connection the problem is exactly the same.

Another oddity is that I can ping the modem without any problems and without any package loss. However, I cannot connect to the web administration interface from my laptop. Curl tells me "connection refused" on port 80 and nmap shows the port as closed. On my android phone I can access port 80 on the same IP address to access the web administration interface of the modem.

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#4 2023-01-11 19:46:32

-thc
Member
Registered: 2017-03-15
Posts: 533

Re: [Solved] Networking issues with T-Mobile modems

Please post the complete (maybe obfuscated, but still intelligible) output of

ip a

and the contents of /etc/resolv.conf.

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#5 2023-01-13 18:32:40

krnlpnc
Member
Registered: 2023-01-11
Posts: 6

Re: [Solved] Networking issues with T-Mobile modems

After further research I found out that there are multiple people having networking issues with this particular modem and some people think it's a problem of the modem hardware itself. I therefore stopped trying to fix the issue and bought a router today (TP-Link Archer A8). I've put the modem into bridge mode and connected the TP-Link router to it. I can now successfully connect to the internet with my laptop.

However, the router is now blocking all my connection attempts (as the modem did before). When I try to open the administration web interface via my laptop, the connection is refused. If I use the router's nameserver, I get "connection refused". There is nothing in the router's log regarding the refused connection attempts. Again, everything is fine on my Android phone and on the other devices in my house. I've cleared all my firewall rules, but no luck. I've now configured a different DNS server and can use the internet without any problems, but I would still like to figure out why I cannot connect to the router.

My guess is that there is some feature that is not supported by my laptop, as I did not have any issues when I was using my old Fritz Box 7530 HF as a router earlier today. I have a Lenovo X250 with an Intel Dual Band Wireless-AC 7265 wifi card.

@-thc should I still post the output of ip a? Here's my resolv.conf:

# Generated by NetworkManager
nameserver 8.8.8.8
nameserver 192.168.0.1

Last edited by krnlpnc (2023-01-13 19:02:27)

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#6 2023-01-13 19:25:31

-thc
Member
Registered: 2017-03-15
Posts: 533

Re: [Solved] Networking issues with T-Mobile modems

krnlpnc wrote:

@-thc should I still post the output of ip a?

Yes.

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#7 2023-01-14 07:30:13

krnlpnc
Member
Registered: 2023-01-11
Posts: 6

Re: [Solved] Networking issues with T-Mobile modems

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
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s25: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 50:7b:9d:42:12:98 brd ff:ff:ff:ff:ff:ff
3: wlp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 4c:34:88:a5:2c:47 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.100/24 brd 192.168.0.255 scope global dynamic noprefixroute wlp3s0
       valid_lft 5826sec preferred_lft 5826sec
    inet6 fe80::95a0:630c:8a01:bedd/64 scope link noprefixroute
       valid_lft forever preferred_lft forever
4: virbr1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:ae:25:38 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.2/24 brd 10.0.2.255 scope global virbr1
       valid_lft forever preferred_lft forever
5: virbr2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:c6:72:4f brd ff:ff:ff:ff:ff:ff
6: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:a2:c0:7d brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
       valid_lft forever preferred_lft forever
7: br-289cda584195: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:98:83:a6:77 brd ff:ff:ff:ff:ff:ff
    inet 172.18.0.1/16 brd 172.18.255.255 scope global br-289cda584195
       valid_lft forever preferred_lft forever
8: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:4c:47:31:a8 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
9: br-923e3e77db3e: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:b4:85:53:ee brd ff:ff:ff:ff:ff:ff
    inet 192.168.16.1/20 brd 192.168.31.255 scope global br-923e3e77db3e
       valid_lft forever preferred_lft forever
10: br-d2225c6646f0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:34:24:4d:b9 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.1/20 brd 192.168.15.255 scope global br-d2225c6646f0
       valid_lft forever preferred_lft forever

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#8 2023-01-14 08:50:17

progandy
Member
Registered: 2012-05-17
Posts: 5,212

Re: [Solved] Networking issues with T-Mobile modems

It looks like you have a bridge which covers the local subnet, so your connections might never make it to your network:

br-d2225c6646f0 - 192.168.0.1/20
wlp3s0 - 192.168.0.100/24

Last edited by progandy (2023-01-14 08:50:31)


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#9 2023-01-14 09:42:23

krnlpnc
Member
Registered: 2023-01-11
Posts: 6

Re: [Solved] Networking issues with T-Mobile modems

Removing the bridge did the trick, now I can reach my router... Thank you all for your help!

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#10 2023-01-14 10:03:58

progandy
Member
Registered: 2012-05-17
Posts: 5,212

Re: [Solved] Networking issues with T-Mobile modems

krnlpnc wrote:

Removing the bridge did the trick, now I can reach my router... Thank you all for your help!

You could also change your router to e.g. 192.168.100.1/24


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