DHCP IP offer not accepted from one DD-WRT router

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tkmds
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Posts: 161
Location: SA

PostPosted: Tue Apr 19, 2022 4:52    Post subject: DHCP IP offer not accepted from one DD-WRT router Reply with quote
There's 4 routers in my setup, all DD-WRT.

P1 - Primary. Runs the DHCP server on 192.168.0.0/24. AC3100.
P2, P3, P4 - Connects to primary above via 1GB LAN, the LAN works fine. RT-AC68U and two RT-AC88U, respectively.

Wifi connections of devices to P1, P2 and P4 work just fine. Device such as iPhones etc connect to P1, P2 and P4 Wireless 5G or 2.4G fine, get an IP and life is good.

Not on P3. A DHCP offer is sent by P1 to P3, but P3 fails to either forward that to a device such as an iPhone or the iPhone fails to receive a DHCP offer from P3.

The iPhone always received a 169.254.149.164 IP and mask of /16.

Went through this for a couple of days, running a few TCP dumps and pouring over the forum posts, can't figure this out yet. I can see a DHCP offer coming into P3 but thereafter fails to reach the external device (iphone in this case)

F/W rules are all permissive. DNS Masquerade is turned off. DHCP server on P3, as with P2 and P4 is off and forwards to P1 for DHCP related requests. P3 does run additonal VLAN's configured via Setup -> Networking and the following commands:

udhcpc -i br1 -p /var/run/udhcpc.pid -s /tmp/udhcpc -O routes -O msstaticroutes -O staticroutes -H DD-WRT-P3 &
udhcpc -i br2 -p /var/run/udhcpc.pid -s /tmp/udhcpc -O routes -O msstaticroutes -O staticroutes -H DD-WRT-P3 &

for VLAN's 10.4.0.0 and 10.4.0.0 for br1 and br2 respectively, so should be unrelated to P1 DHCP running on 192.168.0.0/24. Stopped the above udhcpc commands as well with no affect on the above behavior. All routers run OSPF.

I'm wondering what else I could check to determine why the offered IP is not reaching the IoT devices? Or any commands to dig deeper into why this is not working for this one router? A sample DHCP offer is below that never reaches the IoT device. This message repeats continuously with no success of assign an IP to the IoT device.

This is somewhat related to the VHT160 post I made earlier where VHT160 on this RT-AC88U is not available but another one identical router has VHT160, making me speculate that perhaps there is a general wireless fault with the P3 unit. Even the stock Asus FW does not see VHT160 as being available on this RT-AC88U unit.

Thanks,



Code:
23:54:16.735841 bb:bb:bb:bb:bb:bb > aa:aa:aa:aa:aa:aa, ethertype 802.1Q (0x8100), length 366: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0xc0, ttl 64, id 27979, offset 0, flags [none], proto UDP (17), length 348)
    192.168.0.6.67 > 192.168.0.144.68: [udp sum ok] BOOTP/DHCP, Reply, length 320, xid 0xaf0ee6f3, secs 25, Flags [none] (0x0000)
          Your-IP 192.168.0.144
          Server-IP 192.168.0.6
          Client-Ethernet-Address aa:aa:aa:aa:aa:aa
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Offer
            Server-ID (54), length 4: 192.168.0.6
            Lease-Time (51), length 4: 86400
            RN (58), length 4: 43200
            RB (59), length 4: 75600
            Subnet-Mask (1), length 4: 255.255.255.0
            BR (28), length 4: 192.168.0.255
            Domain-Name (15), length 7: "dom.abc"
            Unknown (252), length 1: 10
            Domain-Name-Server (6), length 20: 192.168.0.30,192.168.0.10,192.168.0.20,123.87.80.1,123.87.81.1
            Default-Gateway (3), length 4: 192.168.0.6
23:54:17.580935 cc:cc:cc:cc:cc:cc > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 594: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 576)
    0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from cc:cc:cc:cc:cc:cc, length 548, xid 0x9035706b, Flags [none] (0x0000)
          Client-IP 192.168.0.210
          Client-Ethernet-Address cc:cc:cc:cc:cc:cc
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Request
            Parameter-Request (55), length 5:
              Subnet-Mask (1), Default-Gateway (3), Domain-Name-Server (6), Domain-Name (15)
              Hostname (12)
            Hostname (12), length 10: "RokuPlayer"
23:54:25.476020 bb:bb:bb:bb:bb:bb > aa:aa:aa:aa:aa:aa, ethertype 802.1Q (0x8100), length 366: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0xc0, ttl 64, id 28795, offset 0, flags [none], proto UDP (17), length 348)
    192.168.0.6.67 > 192.168.0.144.68: [udp sum ok] BOOTP/DHCP, Reply, length 320, xid 0xaf0ee6f3, secs 34, Flags [none] (0x0000)
          Your-IP 192.168.0.144
          Server-IP 192.168.0.6
          Client-Ethernet-Address aa:aa:aa:aa:aa:aa
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Offer
            Server-ID (54), length 4: 192.168.0.6
            Lease-Time (51), length 4: 86400
            RN (58), length 4: 43200
            RB (59), length 4: 75600
            Subnet-Mask (1), length 4: 255.255.255.0
            BR (28), length 4: 192.168.0.255
            Domain-Name (15), length 7: "dom.abc"
            Unknown (252), length 1: 10
            Domain-Name-Server (6), length 20: 192.168.0.30,192.168.0.10,192.168.0.20,123.87.80.1,123.87.81.1
            Default-Gateway (3), length 4: 192.168.0.6

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egc
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PostPosted: Tue Apr 19, 2022 6:56    Post subject: Reply with quote
Not sure if the below applies to your situation but it looks like you setup those routers as a WAP:
A secondary router connected wired LAN<>LAN on the same subnet as a the primary router:
WAN disabled
DHCP server Disabled (=off and NOT set as Forwarder!)
Local IP address in subnet of primary router but outside DHCP scope (you can run udhcpc to give the WAP a static lease but because you can doesn't mean you should Wink
Gateway and Local DNS pointing to primary route
DNSMasq enabled
Router in Gateway mode (the wiki says Router mode but do not do that, Router can break things)

If this is the case then there is no forwarding of DHCP.
As you are using one subnet all requests are handled by the primary DHCP server.
Forwarding DHCP is only between subnets and there is hardly any use case for that in SOHO networks.

You can work with VLANS on a different subnet, if the VLAN originates from the primary router then again that DHCP server (DNSMasq) is handing out the DHCP for that subnet.

If the subnet only runs on a WAP (e.g. for an unbridged VAP) then the DHCP is handled by DNSMasq of the WAP (that is why you keep DNSMasq usually enabled on the WAP but DHCP disabled)

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tkmds
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PostPosted: Tue Apr 19, 2022 13:31    Post subject: Reply with quote
Thanks EGC!

DNS Masquerade Disabled on all and all three below running in DHCP Fowarder mode. Operating mode is OSPF router.

P2, P3, P4

The udhcpc is needed for br1 and br2 which is 10.4.0.0/24 and 10.5.0.0/24. Connecting to these two VLAN's used to work fine.

Though I think you're on to something with DHCP requests not being forwarded correctly.

I should elaborate on the topology a bit further however.

Setup 1:

P1 <-> P2 <-> P3
P1 <-> P4

Setup 2:

P1 <-> P2
P1 <-> P4
P1 <-> Cisco SG200 <-> P3

In both scenarios, the P3 was always behind yet another router be it a DD-WRT one or a non DD-WRT one. All on 1Gbs cable. I'll try to disable DHCP Forwarder on P2, P3 and P4 and report back. And also read your post again. Wink

So far what you posted though makes sense to me. Thanks again!

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tkmds
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PostPosted: Wed Apr 20, 2022 0:28    Post subject: Reply with quote
Clues to the puzzle.

When using P3's 2.4 Ghz frequency band, the DHCP IPv4 address is assigned no problem, alongside the IPv6 address.

When using P3's 5.0 Ghz frequency band, IPv6 DHCP IP allocation works just fine but the IPv4 DHCP assignments is where the issue resides.

Anyway to check the 5.0 Ghz hardware specifically in particular if it's throwing any errors off the device? Confused

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tkmds
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PostPosted: Wed Apr 20, 2022 1:32    Post subject: Reply with quote
As weird as this sounds.

Disabling Implicit Beamforming (and probably even Explicit Beamforming) solved this issue.

I suppose it trying to focus the signal on a fairly old device somewhere on the network, if I'm reading the descriptions correctl? Rolling Eyes

Anyway, this works now. Thanks for the help on this one!

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tkmds
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PostPosted: Sat Jul 02, 2022 21:58    Post subject: Reply with quote
Super strange behaviour with the WiFi chip on this unit.

Disabling:

TurboQAM (QAM256)
NitroQAM (QAM1024)

Effectively keeping all options disabled on the WiFi settings, also results in an IP being assigned through DHCP.



dhcp-no-ip.png
 Description:
 Filesize:  41.08 KB
 Viewed:  2724 Time(s)

dhcp-no-ip.png



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egc
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PostPosted: Sun Jul 03, 2022 12:16    Post subject: Reply with quote
Your settings are far from optimal

Network Mode: AC/N
Never use Auto channel but choose a channel
You should enable SSID Broadcast
ACK timing use at least 1350

Furthermore when you have setup as a WAP DHCP should be off and not set as Forwarder
Usually you should leave DNSMasq as Enabled unless you are really sure you do not need any DHCP handling by that router.

Even when using VLANs (unless you have a really strange (wrong) setup) you should not need OSPF router mode and you could just use Gateway mode.
VLAN's should already be separated at layer 2.

Furthermore I saw mentioning of an RT-AC88U I think that is one of the routers with the DHD bus which is somewhat problematic, but the latest build 49392 has some driver updates which should work better.
For this router there is also an experimental driver which also should work better but maybe not needed after the latest update?

Reset to defaults *after* update and put settings in manually is recommended!

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the-joker
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PostPosted: Sun Jul 03, 2022 14:56    Post subject: Reply with quote
TurboQAM (QAM256) and NitroQAM (QAM1024) are non standard data rate accelerators via additional chips the router uses and not many clients will support these, You need specific Asus HW client side that also supports this.

Otherwise should have no effect I think, but I could be wrong, Broadcom drivers being closed source its hard to tell or fix any related bugs.

If disabling helps, then it could be buggy.

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tkmds
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PostPosted: Mon Jul 04, 2022 0:26    Post subject: Reply with quote
the-joker wrote:
TurboQAM (QAM256) and NitroQAM (QAM1024) are non standard data rate accelerators via additional chips the router uses and not many clients will support these, You need specific Asus HW client side that also supports this.

Otherwise should have no effect I think, but I could be wrong, Broadcom drivers being closed source its hard to tell or fix any related bugs.

If disabling helps, then it could be buggy.


Ah that explains it. Though I was using an Asus ROG connecting to an Asus RT-AC88U running DD-WRT. Taking a look now, the wireless chip is an Intel(R) Dual Band Wireless-AC 7265. Doesn't appear Turbo or Nitro is in any of the Advanced settings so thinking not supported. (Not an Asus device...)

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tkmds
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PostPosted: Mon Jul 04, 2022 1:12    Post subject: Reply with quote
egc wrote:
Your settings are far from optimal

Network Mode: AC/N
Never use Auto channel but choose a channel
You should enable SSID Broadcast
ACK timing use at least 1350

Furthermore when you have setup as a WAP DHCP should be off and not set as Forwarder
Usually you should leave DNSMasq as Enabled unless you are really sure you do not need any DHCP handling by that router.

Even when using VLANs (unless you have a really strange (wrong) setup) you should not need OSPF router mode and you could just use Gateway mode.
VLAN's should already be separated at layer 2.

Furthermore I saw mentioning of an RT-AC88U I think that is one of the routers with the DHD bus which is somewhat problematic, but the latest build 49392 has some driver updates which should work better.
For this router there is also an experimental driver which also should work better but maybe not needed after the latest update?

Reset to defaults *after* update and put settings in manually is recommended!


The OSPF was probably the best thing I ever did. I run about 12 VLAN's all together. Two are defined on one of the DD-WRT routers and work great. The VLAN is communicated across all my switches. Traffic so much smoother on empty VLAN's. I'd go so far as to recommend OSPF for everyone using DDWRT.

Here are my OSPF setup on all the routers.

[ DD-WRT v3.0-r49392 std (06/10/22) - WRT3200 ]
OSPF router

[ DD-WRT v3.0-r49392 std (04/12/22) - AC-RT1300 - Router 1 ] - Internet Facing
tysh OSPF BGP RIP router

[ DD-WRT v3.0-r49392 std (06/23/22) - AC-RT88U - Router 2 ]
OSPF router

[ DD-WRT v3.0-r49392 std (08/13/21) - AC-RT88U - Router 3 ]
OSPF router


+ three Cisco routers and one OpenWRT router also running OSPF.

I can define any VLAN anywhere and all routing is taken care of by OSPF. I can't even imagine going back from this setup. Again, I highly recommend it.


Quote:

Network Mode: AC/N

Done!

Quote:

Never use Auto channel but choose a channel

How to choose the most optimal one?

Quote:

You should enable SSID Broadcast

Considering this. Read about this as well. https://www.pcworld.com/article/447974/5-wi-fi-security-myths-you-must-abandon-now.html#:~:text=Myth%20No.&text=The%20technical%20term%20is%20a,Other%20Network'%20in%20Windows%207. Opted for a FW and encryption. Hence iptables.

Quote:

ACK timing use at least 1350

Done! Set this to 1350.

I'll monitor the router to see over the next short while. Any 2.4 recommendations?



Quote:
Even when using VLANs (unless you have a really strange (wrong) setup) you should not need OSPF router mode and you could just use Gateway mode.
VLAN's should already be separated at layer 2.


I'm actually the one with the strange setup. Smile Take a look at the configs. Included some FW rules as well for example. Immensely happy with this setup.

https://microdevsys.com/wp/dd-wrt-configuring-for-home-with-ospf-and-multiple-vlans/


Quote:

For this router there is also an experimental driver which also should work better but maybe not needed after the latest update?

How do I check this driver version? Quite a few folks are referring to it, but I'm not seeing the forest through the trees here.

Cheers,



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2.4 Ghz WiFi Settings
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2.4-ddwrt-settings.PNG
 Description:
2.4 DD-WRT WiFi settings.
 Filesize:  48.13 KB
 Viewed:  2630 Time(s)

2.4-ddwrt-settings.PNG



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dale_gribble39
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PostPosted: Mon Jul 04, 2022 1:49    Post subject: Reply with quote
tkmds wrote:
Quote:

Never use Auto channel but choose a channel

How to choose the most optimal one?

WiFi Analyzer app on your phone
tkmds wrote:
Quote:

You should enable SSID Broadcast

Considering this. Read about this as well. https://www.pcworld.com/article/447974/5-wi-fi-security-myths-you-must-abandon-now.html

They never talk about any of these myths in conjunction with limiting the max number of associated clients.

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ho1Aetoo
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PostPosted: Mon Jul 04, 2022 6:54    Post subject: Reply with quote
Pooh TurboQAM and NitroQAM have nothing to do with Asus.
This is simply a modulation that is out off spec.

TurboQAM uses 256-QAM, a modulation method that is only officially supported from Wifi5 (IEEE 802.11ac) onwards.
So theoretically all AC devices support this, but the drivers don't always...

NitroQAM uses 1024-QAM, a modulation method that is only officially supported from Wifi6 (IEEE 802.11ax).
So theoretically all AX devices support this, but the drivers don't always...

As already mentioned, it is out of spec to use 256-QAM for Wifi4 and 1024-QAM for Wifi5.

Broadcom always comes up with nonsense to advertise higher data rates.
However, as I said, it is also supported by numerous other chipsets.
the-joker
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PostPosted: Mon Jul 04, 2022 8:51    Post subject: Reply with quote
I only mentioned Asus because they are the only ones who were licensed to add these into their designs back when this was introduced via addon modulation/demodulation chips.

This is still proprietary tech that doesn't belong to Intel afaik (intel are rather Opensource friendly and QAM is not opensource afaik, so even if the standards support it, adding this tech requires paying for it to include the modulators/demodulators in the products, they may have product lines with this support but wont be found easily on most consumer devices.

QAM (up to 4096 QAM) was developed by BroadLogic mainly for video applications which was bought by Broadcom and these days all these wireless Broadcom nonsense been sold to someone else and they are not opensource either, but I dont follow what they have done to this tech recently to be included in IEEE 802.11 specs for AX, AC wave1/2 and N.

Easy to tell, You would get much higher data rates per stream when clients support it.

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Last edited by the-joker on Mon Jul 04, 2022 9:05; edited 1 time in total
ho1Aetoo
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PostPosted: Mon Jul 04, 2022 9:04    Post subject: Reply with quote
Asus doesn't build WLAN chips, they just buy them.
They buy a chip from Broadcom and that's it.

As I said, according to the spec:

Wifi4 IEEE 802.11n max 64-QAM
Wifi5 IEEE 802.11ac max 256-QAM
Wifi6 IEEE 802.11ax max 1024-QAM

All 802.11ac chipsets have the modulators for "TurboQAM".
All 802.11ax chipsets have the modulators for "NitroQAM".

It's just not implemented in the OpenSource drivers - because it's out of spec.
The open source ath10k drivers do not support TurboQAM either - but with a small patch for mac80211 it works without problems.
the-joker
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PostPosted: Mon Jul 04, 2022 9:08    Post subject: Reply with quote
Sausage factory, Asus/(insert brand here) designs/engineers the products and have them built no matter what it is, Laptops/other consumer crap are built by two Companies, mainly Quanta for most OEMS. QAM was/is proprietary tech its no longer owned by Broadcom.

Its not opensource not because its out of spec, but because its proprietary and use to/likely does due to proprietary nature which required specific modulators/demodulators chips.

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