RT-AX86U - Double WAN IPs, What's Going On?

[Ydnaroo]

I noticed last night that I seem to have 2 WAN IPs set?! I thought this might have been due to some of the changes I'd made (still exploring a new router) so I reset everything this morning and having done nothing other than setting the access, WiFi and ISP usernames and passwords, I still get the double WAN IPs and netmask as soon as I connect:

I'm on BT fibre (FTTP) in the UK using automatic WAN IP. Maybe I'm wrong but I'm a little concerned about the second IP and wide netmask! Can anyone help or advise what is happening here?

Quick edit. At the bottom of the Internet Status panel it always seems to says that the Lease has expired and is being renewed, could this be causing the problem?

Edit 2. 169.254.0.0/16 is Rocketnet in Johannesburg!!


(I have done a search in the forum and elsewhere but everything I can find seems to refer to combining 2 connections/IPs when you want to.)

 

[clweb]

No the 169.254.x.x is an Automatic Private Internet Protocol Addressing. This address is generated by the device if a DHCP request fails.
This can be seen on Windows computer when the network has problems.
In your case it is strange because the first IP is a correct BT IP. With the 169.254. address no Internet communication can be made.
Have you configured Dual-WAN ?

 

[Ydnaroo]

No the 169.254.x.x is an Automatic Private Internet Protocol Addressing. This address is generated by the device if a DHCP request fails.

Thanks for that. I knew that exists but had forgotten the IP range. Assume NAT must keep it internal, and keep external out - I hope!. (Have to say https://whois.domaintools.com/169.254.149.30 confused me, didn't read the full info!) Strangely enough, I've just re-downloaded the Merlin firmware, checked the SHA and uploaded and reset the router. Before I got to set anything up the router showed:

I assume there's a problem with the BT ISP at the moment. Having done a basic setup I've still got 2 WAN IPs. The connection works perfectly otherwise.

Have you configured Dual-WAN ?

I haven't and checked it it's not enabled.

Thanks for your help.

 

[Ydnaroo]

If I disconnect both IP's go the 0.0.0.0. When I reconnect the correct IP appears first and the Link-Local address appears a few seconds after. Suspect it's related to the optional second WAN connection even though I don't have one and it's turned off.

No doubt someone will come along and tell me it's perfectly normal. I've just not noticed it before.

Thanks again for your help.

 

[ColinTaylor]

This is normal when using a PPPoE internet connection, e.g. ADSL or VDSL. The 169 address is the local connection to your modem used to create the tunnel and the other address is your public IP address.

 

[Ydnaroo]

This is normal when using a PPPoE internet connection ...

Thanks,

 

[MrC99]

This is normal when using a PPPoE internet connection, e.g. ADSL or VDSL. The 169 address is the local connection to your modem used to create the tunnel and the other address is your public IP address.

Only if the "modem" is acting as a router as well, or if the modem is configure with an IP address on it's LAN side for the purposes of monitoring etc. There's no need for an IP connection with pure PPPoE as they have different ethertypes.

For the OP - suggest checking whether your modem is in bridge or router mode.

 

[Ydnaroo]

For the OP - suggest checking whether your modem is in bridge or router mode.

Definitely set in 'Wireless router mode'. Cheers.

 

[MrC99]

Ah, not the RT-AX86U - whatever it's connected to on its WAN side. If you're in the UK on FTTP are you connected to a BT Smart Hub or similar? I'm not sure if this can be switched to a pure bridge mode but it may be possible to get rid of the APIPA addressing by turning off the DHCP server on the Smart Hub and using static IP addresses. Otherwise if everything's working OK otherwise then probably best to leave well alone.

As an aside I assume you've turned off the wifi on the BT router to cut down performance conflicts there?

 

[Ydnaroo]

Ah, not the RT-AX86U - whatever it's connected to on its WAN side. If you're in the UK on FTTP are you connected to a BT Smart Hub or similar? I'm not sure if this can be switched to a pure bridge mode but it may be possible to get rid of the APIPA addressing by turning off the DHCP server on the Smart Hub and using static IP addresses. Otherwise if everything's working OK otherwise then probably best to leave well alone.

As an aside I assume you've turned off the wifi on the BT router to cut down performance conflicts there?

No, I'm not using the BT Smart Hub. I'm on full fibre to the premises so the fibre terminates in a little box on the wall (ONT) and its ethernet into the RT-AX86U WAN port. There's no option for static IP with BT consumer product. Cheers

 

[MrC99]

Fair enough - we can't get FTTP so no experience with the ONTs but it does look like the Asus is seeing IP packets on the ONT side for some reason. As the ONT is a non user configurable device then looks like seeing APIPA addressing is probably to be expected.

Another option if you're interested would be to install tcpdump on the Asus and check what it's seeing on its WAN interface.

 

[Ydnaroo]

Fair enough - we can't get FTTP so no experience with the ONTs but it does look like the Asus is seeing IP packets on the ONT side for some reason. As the ONT is a non user configurable device then looks like seeing APIPA addressing is probably to be expected.

Another option if you're interested would be to install tcpdump on the Asus and check what it's seeing on its WAN interface.

I've rebooted the ONT and router just in case and noticed that the second Link-Local IP appears even with the ONT off or the WAN cable disconnected (the WAN IP stays at 0.0.0.0). Its like its looking for a second Dual WAN connection even though it's not enabled. It also appears with the Internet Connection turned OFF on the Internet Status panel.

 

[ColinTaylor]

Only if the "modem" is acting as a router as well, or if the modem is configure with an IP address on it's LAN side for the purposes of monitoring etc. There's no need for an IP connection with pure PPPoE as they have different ethertypes.

By setting the Asus' WAN Connection Type to PPPoE (as shown in his screen shot) you are telling it to configure a "typical" home DSL connection. This is not the same as what you're calling "pure PPPoE".

 

[MrC99]

By setting the Asus' WAN Connection Type to PPPoE (as shown in his screen shot) you are telling it to configure a "typical" home DSL connection. This is not the same as what you're calling "pure PPPoE".

AFAICR it is. Configuring any router to use PPPoE on its WAN interface does not require IP. They can co-exist but PPPoE does not imply the use of IP.

 

[grifo]

@Ydnaroo there's an Enable VPN + DHCP Connection option at the bottom of the WAN page in PPPoE mode, try to set that to No and the 169. address should go away.

With it set to Yes the Asus tries to get an IP from the ONT via DHCP but it won't get one as the ONT isn't running DHCP so it self assigns the 169. address to its WAN interface.

 

[Ydnaroo]

@Ydnaroo there's an Enable VPN + DHCP Connection option at the bottom of the WAN page in PPPoE mode, try to set that to No and the 169. address should go away.

Great! Thanks, that's fixed it! Assume that setting must be on by default in the firmware. I can still ping that IP from my computer (after a router reboot) but at least I now know it's nothing malicious.

With it set to Yes the Asus tries to get an IP from the ONT via DHCP but it won't get one as the ONT isn't running DHCP so it self assigns the 169. address to its WAN interface.

That fits in with the warning I was seeing earlier:

Thanks again.

 

[grifo]

You're welcome and yes it's on by default. Not sure why you can still ping that IP, possibly the router is no longer showing it on the GUI but under the hood is still running a DHCP client on the WAN interface, you could try to run ifconfig on the CLI via SSH and see if the IP is still present.

 

[Ydnaroo]

You're welcome and yes it's on by default.

Yep, I've just completely reset the router and didn't use the Quick Setup, the 'Enable VPN + DHCP Connection' selection is made as soon as you select PPPoE.

Might look at the 'ifconfig' later. Thanks again.

 

[Ydnaroo]

Not sure why you can still ping that IP, possibly the router is no longer showing it on the GUI but under the hood is still running a DHCP client on the WAN interface, you could try to run ifconfig on the CLI via SSH and see if the IP is still present.

Just out of interest it's showing as eth0:

eth0      Link encap:Ethernet  HWaddr F0:2F:74:92:2C:88
          inet addr:169.254.149.30  Bcast:169.254.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
          RX packets:1371 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1011 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1208187 (1.1 MiB)  TX bytes:155814 (152.1 KiB)

Thanks again.

 

[grifo]

Just out of interest it's showing as eth0:

Yep, strange as I would have thought that the router would turn off the DHCP client on the the WAN interface (eth0) when that option is turned off.