[RT-N66U] DHCP Reservation

[ezhangin]

Everyone once in awhile my Synology DS413 seems to disappear from my network. It's address is reserved via DHCP Reservation and I was wondering how well it actually works on the RT-N66U? Has anyone else had issues with using it?

It could also be the Synology's fault but I haven't had any problems with it so far. You never know though.

 

[coxhaus]

What do you mean disappears? I don’t think the software which is watching the Synology DS413 is the DHCP software. You might want to try and ping to see if the Synology DS413 is still active on the network.

The DHCP reservation only means the IP address will be allocated to the MAC address for the Synology DS413 when an IP address is requested.

 

[ezhangin]

What do you mean disappears? I don’t think the software which is watching the Synology DS413 is the DHCP software. You might want to try and ping to see if the Synology DS413 is still active on the network.

The DHCP reservation only means the IP address will be allocated to the MAC address for the Synology DS413 when an IP address is requested.

I can't access it via IP. So either the network interface on the Synology is flipping out or it was assigned a different IP.

 

[ezhangin]

Ah, I just learned about find.synology.com

I will try to use this next time the Synology drops off. I could also just exhaustively search my address space. If I can't find it with that or the search I would bet the fault lies with Synology.

 

[coxhaus]

The only way the DS413 would be assigned a different IP address is on reboot of the DS413. If the DS413 is disappearing on reboot then check your router client list. The router should tell you what IP address was assigned.

 

[ezhangin]

As far as I can tell this is during normal operations - not reboot.

 

[Left_Handed_Smoke_Shifter]

Ah, I just learned about find.synology.com

I will try to use this next time the Synology drops off. I could also just exhaustively search my address space.

I note that find.synology.com can't find my DS212+ - and it isn't missing.

I downloaded the Synology assistant from
http://www.synology.com/support/download.php?lang=us

and that was able to find my DS212+ at its manually assigned address.

I apologize for asking an obvious question - but you have also set manual IP configuration on your DS413, as well as on the router, right?

I'm running the new DSM 4.3 on my DS212+

Router: Asus RT-N66R, running Merlin 3.0.0.4.374.32_0

 

[ezhangin]

The Synology is set to DHCP and the router reserves the DS413's address via DHCP. Is this not the way to do it?

 

[Left_Handed_Smoke_Shifter]

I also set the Synology to use static addressing:

Control Panel -> System -> Network -> Network Interface

Choose "Use Manual Configuration" on the "LAN" tab, and enter the static IP address you've set in the router.

This might just be voodoo, but...

 

[ezhangin]

Just did it again. Bunch of error messages all saying "System failed to get external IP"

 

[PrivateJoker]

Just did it again. Bunch of error messages all saying "System failed to get external IP"

Are you assigning manual IPs in the router that are outside the range of its DHCP pool? ie manually assigning (by its MAC) the router 192.168.1.9 and then setting the DHCP pool to only assign ....10:254?

Do that on the router, save & apply, then reboot your NAS. If it's not using the IP you have it automatically (ie you shouldn't have to use any manual settings on the NAS side, it should be DHCP/auto), post screenshots of your static assignment page from your router & the network config on the NAS, and the info > networking box. I can post my screenshots for examples if it'd be handy for you.

 

[ezhangin]

Addresses range from 2 to 254. Router is 1. Everything is either DHCP or reserved via DHCP.

Pinging the Synology seemed to bring the webui back online but it was very slow for a bit. Strange. Rebooting the NAS seems to fix this in general. IIRC rebooting the router did not so I'm thinking it's the Synology.

 

[PrivateJoker]

Addresses range from 2 to 254. Router is 1. Everything is either DHCP or reserved via DHCP.

Pinging the Synology seemed to bring the webui back online but it was very slow for a bit. Strange. Rebooting the NAS seems to fix this in general. IIRC rebooting the router did not so I'm thinking it's the Synology.

Adjust your auto DHCP pool to not overlap with your manual assignments.

 

[ezhangin]

Adjust your auto DHCP pool to not overlap with your manual assignments.

By manual, did you mean static or reserved DHCP? I would think the DHCP server would know not to use something it reserved. I guess another device could hash to the same IP though.

 

[PrivateJoker]

By manual, did you mean static or reserved DHCP?

I meant manually reserve an IP address on the router for the MAC & IP you want for your client device. I think "static" and "reserved" are kind of interchangeable, same ends. You can leave your client in auto DHCP mode, you don't need to input the client side settings manually.

I would think the DHCP server would know not to use something it reserved.

No it's not that smart, search through these threads - having your static chunk numerically separated from your auto chunk is best practice, you're experiencing what happens when you don't do that.

I guess another device could hash to the same IP though.

No hashing comes into play in the assignment of IPs in a home/SOHO router setup. Perhaps if you were on an actual domain with a name server or doing something else outside the sphere of small networks. IP addresses are constantly being renewed with the router, sometimes clients aren't up on the network when their IP lease is up, etc. If auto assignment to your clients is on, it's safe to bet that you can't trust anything to remain on a specific IP for an extended length of time.

 

[saintdev]

I meant manually reserve an IP address on the router for the MAC & IP you want for your client device. I think "static" and "reserved" are kind of interchangeable, same ends. You can leave your client in auto DHCP mode, you don't need to input the client side settings manually.

I'm sure you probably know this, but let's clarify some terms here. I don't think everyone is on the same page. A static address is one manually assigned on the device, DHCP never comes into play in this situation. A reserved address is one where the DHCP server assigns the same IP address to the same MAC address every time.

If I understand correctly ezhangin is stating he has a reserved address assigned to his NAS on the router. Someone suggested he try a static address to see if it fixes the issue (unclear if he attempted this).

I would think the DHCP server would know not to use something it reserved.

No it's not that smart, search through these threads - having your static chunk numerically separated from your auto chunk is best practice, you're experiencing what happens when you don't do that.

While you are correct about not having static IPs overlap your DHCP pool, ezhangin is also correct about dnsmasq being smart enough to not assign reserved IPs. Unfortunately the dnsmasq man page makes no such guarantee, but Simon Kelley confirms that reserved IPs are excluded from the list of available IPs for DHCP assignment (except for to their assigned MAC).

No hashing comes into play in the assignment of IPs in a home/SOHO router setup. Perhaps if you were on an actual domain with a name server or doing something else outside the sphere of small networks. IP addresses are constantly being renewed with the router, sometimes clients aren't up on the network when their IP lease is up, etc. If auto assignment to your clients is on, it's safe to bet that you can't trust anything to remain on a specific IP for an extended length of time.

Actually, dnsmasq explicitly uses a hash of the client's MAC so that IPs will remain stable long-term. See the entry for --dhcp-sequential-ip on the dnsmasq man page.

As for the original problem, just a wild guess, but could it be the NAS is going into some sort of power saving mode, where it takes a few seconds to wake up after it detects network activity directed at it?

 

[PrivateJoker]

I'm sure you probably know this, but let's clarify some terms here. I don't think everyone is on the same page. A static address is one manually assigned on the device, DHCP never comes into play in this situation. A reserved address is one where the DHCP server assigns the same IP address to the same MAC address every time.

Right, I was trying to be clear that adjustments do not need to be made at both the router, and the client (NAS in this situation).

Someone suggested he try a static address to see if it fixes the issue (unclear if he attempted this).

I think that someone was me, perhaps others as well, and yes it is unfortunately unclear if he attempted this.

While you are correct about not having static IPs overlap your DHCP pool, ezhangin is also correct about dnsmasq being smart enough to not assign reserved IPs. Unfortunately the dnsmasq man page makes no such guarantee, but Simon Kelley confirms that reserved IPs are excluded from the list of available IPs for DHCP assignment (except for to their assigned MAC).

I was going on my gut. My gut owns the same router as OP & a very similar Synology NAS.

Actually, dnsmasq explicitly uses a hash of the client's MAC so that IPs will remain stable long-term. See the entry for --dhcp-sequential-ip on the dnsmasq man page.

Interesting...I thought a "hash" was made from an input whose length varied to an output that was fixed. Every MAC is a fixed length of 3 octets long, so I don't know (nor is it probably relevant for this guy's question) how or why it gets truly hashed for purposes of a DNSmasq. How does an IP "remain stable long term" anyway when their leases are getting renewed by the router on a relatively short term basis?? Wait wait, don't answer - I will wait for a rainy day and look it up. I want to heighten my suspense.

As for the original problem, just a wild guess, but could it be the NAS is going into some sort of power saving mode, where it takes a few seconds to wake up after it detects network activity directed at it?

The suggestions I provided have given me easy, reliable access to my Synology NAS (whether it's asleep or alive) on my RT-N66U.

Thank you for your clarifications.

 

[ezhangin]

I'll give a static address a try I suppose. Or reduce the address space available to the DHCP server and let it reserve an address for the NAS outside the DHCP address space. Maybe I'll try both. I just find it weird that the Synology is reporting that it can't get an external IP at all.

I highly doubt the Synology is going into power save mode based on it's usage patterns.

About the hashing on this particular platform: I do believe addresses from DHCP are hashed. I haven't looked at the code in awhile but IIRC if your network remains more or less the same, devices will end up with the same IP each lease (assuming it isn't taken). I don't use this fact in any way but I always found it interesting.

Another interesting fact is that I don't remember this happening in the past. Unfortunately I don't remember exactly when it started and there have been numerous updates to both the NAS and the router.