24.10.0 WRT1900ACS Vodafone (KDG/Kabeldeutschland) cablemodem DHCP issues

Installing and Using OpenWrt
1

Dear all,

I finally "upgraded" my WRT1900ACS router from 22.03 to 24.10.0. As the previous upgrade attempt to 23.x failed, I did a factory reset, installed a factory 24.10.0 image and then piece by piece copied back my old configuration. Last time the network configuration seemed to have been the culprit, due to the change to DSA switch infrastructure (or whatever it was called).

I got the network running, including VLANs and Wireguard tunnels and things like that.

But one thing I noticed is that getting the WAN IP via DHCP is ... flaky at best.

I am running the WRT1900ACS behind a Vodafone cable modem running in "bridge mode". That is, the cable modem only acts as a modem, not as a full fledged router. Hence my router's DHCP request gets forwarded to Vodafone's infrastructure and I get a public IPv4 address. (IPv6 is not possible and currently not configured). That was working fine with IPv4 on 22.3, but now mostly the router does not get an IP address via DHCP at all.

I made sure to enable the broadcast option that I already had enabled on 22.x and which seems to be required to be able to get an IP address via DHCP in case the last restart of the cable modem is more than 15 minutes ago.

I now managed to get an IP by restarting the cable modem and restarting the WAN interface. Either it does not get an IP, it gets a 192.168.x.y IP or after several attemps I got a proper public IP.

(Once it got an IP address from a completely different range than what I
normally have, 31.1.x.y instead of 88.x.y.z/24)

I just checked and apparently there a no outages or problems reported with
Vodafone's infrastructure in my region. As this seemed to be working properly with 22.3 I would guess this is on OpenWRT's side.

Is anyone else having such issues?

Kind Regards,
Johannes

2

Forgot to add the relevant section from /etc/config/network:

config interface 'wan'
        option device 'wan'
        option proto 'dhcp'
        list dns '46.182.19.48'
        list dns '80.241.218.68'
        list dns '159.69.114.157'
        option peerdns '0'
        option broadcast '1'
        option hostname '*'
        option delegate '0'
3

As a very first debugging step, check if the WAN MAC address remains the same between (re-)boots.

1 Like
4

Yes, it does. This is the configuration part from /etc/config/network:

config device
        option name 'wan'
        option macaddr '62:38:e0:d7:51:df'

(The UI shows the MAC in UPPERCASE, the file is lowercase, for whatever reason).

5

You can be lucky, I get DHPC and DNS all the time but it never works...since start of February ;- ) I used bridged Mode for a decade but since last month it works only if I connect a client PC direct to the cable modem. As soon as a router is involved I am cut off connection. Probed different router with 23.05 and 24.10, also one with OEM firmware.

Vodafone West GmbH has changed / is changing network behavior or has some problems regarding their network. Or both at the same time ;- )

Their support is a nightmare...the last tickets from my side are closed without comments or notice. You only can see it if you log in and look at your ticket.

From my point of view it seems this is all intended, at least in my case. owed to the fact that vodafones customer support acted uninformed, reluctant, was ignoring the facts, proposed absurd "solutions" and, at some point, was fighting actively against me and the problem .

PS: Used to have random MAC on WAN, now a fixed one but no dice

#Vodafone #Kabelmodem #Verbindungsprobleme #KeinInternet #BridgeMode

6

remember that most cable companies have a pesky behavior, when the cable modem is in bridge mode:

as soon as you attach a client/router device with a new/different MAC, you no longer have connection via the modem. The network allows and caches only a single MAC.

It might need a reboot of the modem (in bridge mode) and sometimes additional waiting of 10-15 minutes (or more) before the cable network accepts a new WAN MAC of the device which is connected to the bridge-mode-modem.

This means quick-testing via client or MAC changes due to router updates easily takes you into a no-connection-situation.
If you are not aware of this, you are provider-disconnected and don't understand why and you might unaware repeatedly swap connected devices (which actually causes and continues the connection trouble)

2 Likes
7

True, but after more than 10 years I learned my lesson ;- ) Direct connected Clients work 'instantly'

8

Could it be the 1900acs leaks lan side MAC addresses during bootup, potentially exhausting the allowed number of MAC limit?

9

Could it be the 1900acs leaks lan side MAC addresses during bootup, potentially exhausting the allowed number of MAC limit?

I have no idea. But if so, it would have done so on 22.3 already, right?

10

Was it using DSA on 22.3 already?

11

Was it using DSA on 22.3 already?

No, I don't think so. You mean that could introduce the leak?

Any idea how to test/prevent that?

12

Testing is easy, just connect the router's wan port to a computers ethernet port, start tcpdump/wiresharkbon te PC on the connected interface and record all packets from startup, if you see multiple MACs from the router this likely implies some leakage...

1 Like
13

I had a similar issue with vaderphone in DE.
Details here Router gets public WAN IP but no internet connection
Or long story short:

image
image547×327 7.32 KB

which is equal to

config interface 'wan'
option device 'eth1'
option proto 'dhcp'
option vendorid 'openwrt' <-- this one here
option peerdns '0'

in /etc/config/network

I hope this helps.

1 Like
14

Thanks @tomtom, I'll give it a try. Today getting an IP seems to be working.

What still does not work is getting a reliable internet connection, see this thread. Not sure if this is related to Vodafone or just an error on my side...

15

That was the point where I decided, that the bridge mode of their router is nuts. Vodafone can do IPv6 pretty well, but their bridge mode is limited to IPv4. They confirmed this in a phone call to their support. Sounds like sth. self coded strip down of the connection which nobody maintains anymore?

I bought an own cable router and use this one and a nested openwrt device behind it. This works quite good and I have both public IPv4 and a public IPv6 /56 prefix.

Worth to mention I am not at Vodafone west, which is technically different.

2 Likes