Clients on br0 not getting IP

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hsar
DD-WRT Novice


Joined: 30 Apr 2021
Posts: 8

PostPosted: Mon Jun 14, 2021 16:04    Post subject: Clients on br0 not getting IP Reply with quote
The goal: having one interface for WAN and the rest bridged (emulating a common router that is).

Tested on Hyper V, 5 virtual switches.
Clean DD-WRT x86_86 install / tried several builds, with 5 virtual NICs - each on its own virtual switch.
Selected DHCP in basic setup (as expected, eth0 was assigned to WAN and eth1-4 in br0).
All seem good - the interace is accessible from the outside world:8080.

The problem:
Clients connected to eth1-4 are not getting IP via DHCP.
In syslog, I can see DHCPDISCOVER(br0)/DHCPOFFER(br0), with legit mac and ip offerings, but no DHCPREQUEST/DHCPACK.

By changing e.g. eth1 to unbridged (setup/networking), both of the bellow assign IP to clients:
1) using a different (from the one in the basic setup page) ip/subnet and 2nd DHCP, clients get IP from the 2nd DHCP.
2) using the router's ip, as defined in the basic setup (192.168.1.1), and without setting up a new DHCP, clients get IP from the DHCP range defined in the basic setup.

If i set all interfaces (eth1-4) to 'unbridged/nat', and specify for all the router's IP, everything seem to be working.
But, shouldn't that be the case when just setting the WAN connection type as static or auto/DHCP?

Note:
- Quite familiar with DD-WRT, but new to the x86 version.
- Mostly windows background (IT & programming) with some linux/routing knowledge - mostly thanks to using DD-WRT.
- All tests performed on 'public' builds. Got one of the licenses I'll be needing - haven't used it yet, due to, well, testing...
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Wildlion
DD-WRT Guru


Joined: 24 May 2016
Posts: 1410

PostPosted: Mon Jun 14, 2021 22:49    Post subject: Reply with quote
what are your dhcp settings in dd-wrt?

More than likely if you are getting to there then your clients are not seeing DHCPOFFER. Have you done a wireshark on the client to see if it is seeing that packet?

Otherwise is there something else on Hyper V preventing the packets, or is a firewall blocking the unicast vs the broadcast traffic?

I was assuming these are direct connections (ie nothing else on the network) but are they, ie is there nothing else with that same subnet or packets getting forwarded off on a different route?
hsar
DD-WRT Novice


Joined: 30 Apr 2021
Posts: 8

PostPosted: Tue Jun 15, 2021 3:56    Post subject: Reply with quote
Thanks for the reply/interest.

Have tried various approaches: disabled DHCP in the basic and setup dhcp in the 'additional dnsmasq options' box, created a second bridge to see if something was wrong with br0 - same result.
Firewalls are disabled, hyper-v's 'dhcp guard' is off - nothing else in the subnet.
Tried with a single physical adapter with virtual machines and with a second pc and two physical adapters.
However, it turns out, it is not (just) a DHCP issue.
By setting static IP on a laptop connected to a bridged connection (with IP e.g. 192.168.1.7/24), I can't ping br0 (192.168.1.1).
By unbridging the interface and setting it's IP to be the same as br0's (192.168.1.1 - should this even be accepted?), not only ping works, but by switching from static to DHCP the client gets an IP from the primary pool - without having to assign a new DHCP range for that interface that is.

So, it seems br0 can hear the clients connected to the bridged interfaces (according to the DHCP request log), but can't actually talk to them (haven't verified with wireshark).

The thing is that, for my x86 setup, I don't intend to use bridge - or even a second interface. The plan is to use it for openvpn with the outside world, and change some existing wireguard router-to-router connections to x86-to-router. The problem reported here was observed right after installing x86, and have spent the last couple of days trying to figure the cause (and admittedly, learning a lot in the process).
hsar
DD-WRT Novice


Joined: 30 Apr 2021
Posts: 8

PostPosted: Tue Jun 15, 2021 12:38    Post subject: (solved) Clients on br0 not getting IP - Hyper V Reply with quote
Solved.
It was a Hyper-V security setting.
MAC address spoofing must be enabled (checked) on the vnics assigned to a vm for the bridged interfaces to be allowed to communicate with clients (using a different macaddr from the one specified/assigned to them upon adding them to the virtual machine).
Wildlion
DD-WRT Guru


Joined: 24 May 2016
Posts: 1410

PostPosted: Fri Jun 18, 2021 1:21    Post subject: Reply with quote
that sounds right, because in Virtualbox you ahve to change permiscous mode to be allow all. I think it is because dd-wrt needs some lower level access on the LAN side, but it does not matter on the WAN.

Glad you got it working
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