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ASUS Dual WAN Failover, Then Failback, Leaves Secondary LAN in "Hot Standby"

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AndrewL733

Occasional Visitor
Hello all,

I have an RT-AC68U with 386.12.4 firmware. I am successfully running a Dual WAN with the Secondary WAN set up for Failover + Failback. (I'm actually kind of surprised it works so reliably, given the many references I'v seen in this forum to a user-script to take the place of the native ASUS Failover code. See: https://www.snbforums.com/threads/dual-wan-failover-v2-release.83674/ )

Anyway, I do have one serious problem with the native ASUS Failover/Failback feature. When my router "fails back" to the Primary WAN, it leaves the Secondary WAN in "Hot Standby" and both WAN paths are actually still accessible. Something I don't want. I'll explain this all in detail below, but this is a problem for me because I have a "VPN Appliance" (home-made little box, running Ubuntu + Wireguard + GRETAP to create a layer-2 virtual ethernet switch) that continues sending traffic over the Secondary WAN even once the Primary WAN is back up. Given that my Secondary WAN is a 4G/LTE device, this has caused me to run out of mobile data on my SIM card.

I have come up with a workaround to solve my problem (so that I don't keep running out of data). I am using a "wan-event" user script to detect when WAN ports get connected and disconnected and to send me an email notification. And then I'm also calling another script that checks to see if both WAN 0 and WAN 1 are up at the same time, and if "yes" I reboot the router to get back to a state where my Secondary WAN is in "Cold Standby". It works. But it would be better to fix the failover/failback feature. I have sent this information to ASUS but I'm kind of skeptical they'll ever get back to me. Maybe someone here knows what's the problem and how to fix it? So, here's the long story (as sent to ASUS support).

(PART 1. PART 2 CONTINUES IN REPLY)

Topology / Configuration

  • ASUS RT-AC68U is configured in Dual WAN mode
  • WAN port is connected to ASKEY HGU RTF3505VW Fiber Router. Router is configured in “Bridge” Mode, so ASUS Router gets the public IPV4 address
  • LAN port 2 is designated for secondary WAN and is connected to a TP-LINK TL-MR100 4G/LTE Router.
After first booting up router, the Secondary WAN is in “Cold Standby”. This is Good!
Screenshot 2024-01-24 at 6.24.36 AM.png


Primary WAN (ppp0) is “UP” and has a public IP address


Code:
ppp0      Link encapoint-to-Point Protocol
          inet addr:88.1.XXX.XXX  P-t-P:192.168.144.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING MULTICAST  MTU:1492  Metric:1
          RX packets:9347 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10132 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:4843312 (4.6 MiB)  TX bytes:2841385 (2.7 MiB)

Secondary WAN (vlan3) is “DOWN” and does not have an IP Address

Code:
vlan3     Link encap:Ethernet  HWaddr 385:47:1F:5A:12
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:4756 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1236450 (1.1 MiB)  TX bytes:0 (0.0 B)

10: vlan3@eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
    link/ether 38:d5:47:1f:5a:12 brd ff:ff:ff:ff:ff:ff

Routing Table Shows Only Primary WAN (ppp0) Listed:

Code:
asusadmin@RT-AC68U-5B30:/tmp/home/root# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
8.8.4.4         192.168.144.1   255.255.255.255 UGH   1      0        0 ppp0
192.168.144.1   0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
8.8.8.8         192.168.144.1   255.255.255.255 UGH   1      0        0 ppp0
10.16.0.0       192.168.15.1    255.255.255.0   UG    1      0        0 br0
192.168.101.0   0.0.0.0         255.255.255.0   U     0      0        0 br1
192.168.102.0   0.0.0.0         255.255.255.0   U     0      0        0 br2
192.168.15.0    0.0.0.0         255.255.255.0   U     0      0        0 br0
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 vlan2
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         192.168.144.1   0.0.0.0         UG    0      0        0 ppp0

I simulate a failure of the primary WAN by pulling the fiber cable out of the ASKEY ROUTER. I don't touch the Ethernet connection between ASKEY and ASUS routers.
After Failover, the Secondary WAN shows "Connected" and the Primary WAN is in “Cold Standby”. Good! I have Internet access on my LAN going through the 4G/LTE router.

Screenshot 2024-01-24 at 6.56.34 AM.png



Indeed, the Primary WAN (ppp0) is DOWN

Code:
asusadmin@RT-AC68U-5B30:/tmp/home/root# ifconfig ppp0
ifconfig: ppp0: error fetching interface information: Device not found

The Secondary WAN (vlan3) is UP and has a “LAN ADDRESS” issued from the TP-LINK 4G/LTE ROUTER. (by the way, I don't care about double NAT here).
Code:
vlan3     Link encap:Ethernet  HWaddr 385:47:1F:5A:12
          inet addr:192.168.5.100  Bcast:192.168.5.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:16251 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1578 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:4436327 (4.2 MiB)  TX bytes:443561 (433.1 KiB)

Routing Table Shows VLAN3 in use and does not show any entries for ppp0
Code:
asusadmin@RT-AC68U-5B30:/jffs/downloads# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.5.1     *               255.255.255.255 UH    0      0        0 vlan3
8.8.4.4         192.168.5.1     255.255.255.255 UGH   1      0        0 vlan3
8.8.8.8         192.168.5.1     255.255.255.255 UGH   1      0        0 vlan3
10.16.0.0       192.168.15.1    255.255.255.0   UG    1      0        0 br0
192.168.101.0   *               255.255.255.0   U     0      0        0 br1
192.168.5.0     *               255.255.255.0   U     0      0        0 vlan3
192.168.102.0   *               255.255.255.0   U     0      0        0 br2
192.168.15.0    *               255.255.255.0   U     0      0        0 br0
169.254.0.0     *               255.255.0.0     U     0      0        0 vlan2
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         192.168.5.1     0.0.0.0         UG    0      0        0 vlan3

At this point, my VPN Appliance is sending data out to the Internet via the vlan3 interface on the ASUS router. Still all good.
Now I plug the Fiber cable back into my ASKEY ROUTER
 

Attachments

  • Screenshot 2024-01-24 at 6.23.51 AM.png
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PART 2

NOW I PLUG FIBER CABLE BACK INTO ASKEY ROUTER

After Failback, Primary WAN connected and Secondary WAN in “Hot Standby”. BAD!


Screenshot 2024-01-24 at 6.23.51 AM.png


Primary WAN (ppp0) is UP and has a public IP address again:

Code:
ppp0     Link encapoint-to-Point Protocol
          inet addr:88.1.192.55  P-t-P:192.168.144.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING MULTICAST  MTU:1492  Metric:1
          RX packets:9728 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12919 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:3111396 (2.9 MiB)  TX bytes:11329948 (10.8 MiB)

Secondary WAN (vlan3) is ALSO UP and has a TP-LINK LAN IP address again:

Code:
vlan3     Link encap:Ethernet  HWaddr 385:47:1F:5B:31
          inet addr:192.168.5.100  Bcast:192.168.5.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:67892 errors:0 dropped:0 overruns:0 frame:0
          TX packets:57967 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:44386470 (42.3 MiB)  TX bytes:14823597 (14.1 MiB)

Routing Table shows both Primary and Secondary WANs are accessible. There are entries for both networks.

Code:
asusadmin@RT-AC68U-5B30:/tmp/home/root# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.5.1     0.0.0.0         255.255.255.255 UH    0      0        0 vlan3
8.8.4.4         192.168.144.1   255.255.255.255 UGH   1      0        0 ppp0
8.8.4.4         192.168.5.1     255.255.255.255 UGH   1      0        0 vlan3
192.168.144.1   0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
8.8.8.8         192.168.144.1   255.255.255.255 UGH   1      0        0 ppp0
8.8.8.8         192.168.5.1     255.255.255.255 UGH   1      0        0 vlan3
10.16.0.0       192.168.15.1    255.255.255.0   UG    1      0        0 br0
192.168.101.0   0.0.0.0         255.255.255.0   U     0      0        0 br1
192.168.5.0     0.0.0.0         255.255.255.0   U     0      0        0 vlan3
192.168.102.0   0.0.0.0         255.255.255.0   U     0      0        0 br2
192.168.15.0    0.0.0.0         255.255.255.0   U     0      0        0 br0
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 vlan2
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         192.168.144.1   0.0.0.0         UG    0      0        0 ppp0

At this point, my VPN Appliance should be using the Primary WAN but in fact it is still sending and receiving data through the Secondary WAN, using up all my mobile data.

To avoid this problem, I believe the ASUS Router should have put the Secondary WAN back into "Cold Standby". I tried to simulate this by deleting the vlan3 references from the routing table but I'm not convinced that was a good idea, and I'm worried that doing this could make a future failover unreliable. Perhaps another approach would be to simply bring the vlan3 interface down with "ifconfig vlan3 down"?

In any event, as I wrote at the top, I just worked around the problem by creating a "wan-event" script, detecting whether both interfaces were "up", and if "yes" rebooting the router. When the router comes back up it has the Secondary WAN in "Cold Standby" and all is good again.

But really, in my opinion, ASUS should fix this. Most ASUS users aren't going to move over to asuswrt-merlin, and even if they do most won't write user scripts. There is no reason to have the Secondary LAN in "Hot Standby" in a Failover / Failback configuration.

Perhaps the asuswrt-merlin community can contribute a fix to ASUS if ASUS doesn't fix it themselves?
 
Last edited:
Hello @Kingp1n,

Can you tell me what exactly isn’t working with the ASUS version of Failover. I’m finding it working perfectly except for this one issue where after Failback I have the Seconday WAN in “Hot Standby” instead of “Cold Standby”. Is this something the script you linked to fixes?

Andrew
 
Hello @Kingp1n,

Can you tell me what exactly isn’t working with the ASUS version of Failover. I’m finding it working perfectly except for this one issue where after Failback I have the Seconday WAN in “Hot Standby” instead of “Cold Standby”. Is this something the script you linked to fixes?

Andrew
They're quite of few issues with the Asus version scattered thru these forums. The script addresses all these issues and makes Dual-WaN work as intended.
 

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