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Author Topic: Routing between two subnets  (Read 227 times)

Cris70

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Routing between two subnets
« on: April 10, 2020, 04:27:09 PM »

Hi all, this is my first post on this forum.
I recently bought a D-Link DIR-882 to replace my ancient TP-Link router.
While configuring the router, I forgot that I had a device configured with a static IP on 192.168.1.20.
The new router is configured to assign addresses in the range 192.168.0.100 - 192.168.0.199, and I've already done quite an amount of configuration both in the router and in the connected devices.
Now I'm stuck with the device that is on 192.168.1.20: I cannot reach it to reconfigure it.
I tried to change the netmask on the Network page to 255.255.254.0, so that the router should now be seeing the 192.168.1.x subnet too.
Actually, I see that the device is now appearing in the "connected clients". However, I still cannot reach it.
A traceroute stops responding right after the first hop.
Is there a way to make it work correctly?
I tried to setup a static route, too, but it appears that the DIR-882 only supports WAN static routes.
I saw in the forums that there is a hack to allow for LAN static routes, but it seems it works only on rather old firmware versions.
Any hints?

Thank you in advance!
Cris
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Cris70

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Re: Routing between two subnets
« Reply #1 on: April 10, 2020, 04:32:02 PM »

Forgot to say that I'm on Firmware Version: 1.20
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me_iauras

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Re: Routing between two subnets
« Reply #2 on: April 11, 2020, 03:39:35 AM »

Wouldn't it be easier just to change the IP of the old equipment to the new subnet ?
The issue i think is that the old equipment is still under the impression that it's running in a /24 subnet with the gateway 192.168.1.1 which doesn't exist anymore so it doesn't really have any way to reply since it's network is 192.168.1.1>.254 and the gateway witch it's trying to reply through no longer exists to do the routing for it .
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Cris70

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Re: Routing between two subnets
« Reply #3 on: April 11, 2020, 03:54:26 AM »

Hi me_iauras!

Wouldn't it be easier just to change the IP of the old equipment to the new subnet ?

Yes it would, if only I could reach it! Keep in mind that this is a remote device and due to the covid lockdown I cannot physically reach it.
So I should reach its web configuration ui, but since the packets don't route to it... it'a catch-22

The issue i think is that the old equipment is still under the impression that it's running in a /24 subnet with the gateway 192.168.1.1 which doesn't exist anymore so it doesn't really have any way to reply since it's network is 192.168.1.1>.254 and the gateway witch it's trying to reply through no longer exists to do the routing for it .

No, the problem here is that the device was configured with a static IP (not a reservation on the router) so it still insists that it wants to be on the 192.168.1.x subnet.

What I do not understand, is why the router is not able to route the packets correctly.

BTW, thank you for your reply!
Cris
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Cris70

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Re: Routing between two subnets
« Reply #4 on: April 11, 2020, 04:24:10 AM »

Replying to myself: I got it sorted out.
I simply configured my tablet to get a static IP on the 192.168.1.x subnet. With that done, I could reach the other device and reconfigure it.
Then I configured back my tablet on DHCP. Should have thought it before!!
Thank you for your help.
Cris
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me_iauras

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Re: Routing between two subnets
« Reply #5 on: April 11, 2020, 04:28:12 AM »

OK ; did not really thought you were talking about reaching  it physically but logically as in via the network . I thought that the router you replaced was in your house not on some remote site (workplace or otherwise ) 
Regarding the second part .. I understood that the equipment is with static IP configuration ; my point was that from it's perspective it doesn't know how to reply to the incoming packets it receives from 192.168.0.x IPs . From it's perspective (I assume that it is configured 192.168.1.20 255.255.255.0 netmask and 192.168.1.1 gateway) local LAN means 192.168.1.1 to 192.168.1.254 . Everything else must be routed through it's configured gateway , the old router with 192.168.1.1 which no longer exists so when it tries to forward the reply packages to the 192.168.0.x initial sender IP the gateway through which it;s trying to achieve this is no longer there to perform the task .
The solution would be to forgo the configurations made specific to 192.168.0.0/24  subnet and change the subnet to match what the equipment recognizes (192.168.1.0/24). If the IP's are given through DHCP reservations and not through manual IP configuration on each equipment normally I think that all rules will change accordingly ( what configuration have you done since appart for port fw I can't really think of any other which may be impacted since the firware has such limited options of configuration)
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Cris70

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Re: Routing between two subnets
« Reply #6 on: April 11, 2020, 04:37:38 AM »

Hi me_iauras

Regarding the second part .. I understood that the equipment is with static IP configuration ; my point was that from it's perspective it doesn't know how to reply to the incoming packets it receives from 192.168.0.x IPs . From it's perspective (I assume that it is configured 192.168.1.20 255.255.255.0 netmask and 192.168.1.1 gateway) local LAN means 192.168.1.1 to 192.168.1.254 . Everything else must be routed through it's configured gateway , the old router with 192.168.1.1 which no longer exists so when it tries to forward the reply packages to the 192.168.0.x initial sender IP the gateway through which it;s trying to achieve this is no longer there to perform the task.

You're absolutely right, I did not think about it in this perspective.
So even if the packets could reach it, it wouldn't have been able to reply.
Thank you for clarifying this, could turn out to be useful in the future!
Cris
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