Author Topic: RRC-1258 DNS Cache  (Read 8531 times)

g4swx

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RRC-1258 DNS Cache
« on: 2011-05-10, 18:52:29 »
My overall experience of the RRC is great.
However I have experienced a strange DNS failure a few times and I am wondering if it has something to do with the length of time that the RRC-1258 caches DNS. I am currently running 2.35 firmware and a dyndns address.

I have recently been suffering from intermittent operation on my control ADSL connection. As a result the IP address changes to another from the DHCP pool. You would think that this would not matter but after the customary connection failure when I try to reconnect from the control RRC to the radio and the connection attempt fails. The control RRC status indicates that the DNS status is unresolved... However with a PC on the same LAN I have no issues in connecting to the radio webserver even if I clear the PC's DNS cache and start again. The only difference as far as I can see is that I have entered my ISP's primary DNS server in the control RRC IP settings whereas the PC gets the DNS server address from by DHCP from my local router.
It does resolve, but not very quickly

Any thoughts?
John G4SWX

g4swx

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Re: RRC-1258 DNS Cache
« Reply #1 on: 2011-05-10, 21:42:50 »
More - I have just suffered the same problem

The Radio side is fine (actual IPs changed):
Status
Name Value
Radio ON
SIP status Error
Last SIP error SIP Error
RTP Timeout 0
SIP Timeout 0
Rx Jitter buffer size 4
Rx Jitter delay 3
External IP xx.yy.164.232
SIP Out port 6060
SIP In port 6060
Audio Out port 1029
Audio In port 11500
Command Out port 1029
Command In port 12500
External SIP In port 6060
External Audio In port 11500
External Cmd In port 12500
Other party xx.yy.50.217
Input 1 High
Input 2 High
Output 0 Low
Output 1 Low
Output 2 Low
DynDns status OK
Ping status (watchdog) Off
Active profile: Default
PTT status: OFF

However the controller has lost the DNS status because of a network break at the controler end:

Status
Name Value
Control panel ON
Radio OFF
SIP status Error
Last SIP error SIP Error
RTP Timeout 0
SIP Timeout 0
Rx Jitter buffer size 16
Rx Jitter delay 3
SIP Out port 6060
SIP In port 6060
Audio Out port 11500
Audio In port 11500
Command Out port 12500
Command In port 12500
External SIP In port 6060
External Audio In port 11500
External Cmd In port 12500
Other party xx.yy.164.232
Input 0 High
Input 1 High
Input 2 High
Output 0 High
Output 1 Low
Output 2 Low
DNS status Error, failed to resolve xxxxx.ham-radio-op.net!
Active profile: Default
PTT status: OFF

Simply rebooting the controler is not enough.

John G4SWX


Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #2 on: 2011-05-11, 14:58:44 »
To me it sounds like the ADSL breakdown also makes the ISP's DNS Server inaccessible and so the control RRC fails resolving, while the PC might still work ok since its DNS is the local router which I assume is accessible even it the ADSL is disconnected. Why not try entering your local router as DNS server for the RRC too just to see what happens then?
Always include type of hard/software and version when asking for support.

g4swx

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Re: RRC-1258 DNS Cache
« Reply #3 on: 2011-05-11, 18:55:46 »
I don't think that is down to the ISP, I selected Google DNS on 8.8.8.8 and still had the same occasional problem. I will try setting the DNS server as the ADSL gateway
I also had an issue with the remote failing to update with DynDns (error 8 - I think) which remained until I remotely rebooted the RRC.
73
John

g4swx

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Re: RRC-1258 DNS Cache
« Reply #4 on: 2011-05-13, 12:35:41 »
I looked at the configuration between the RRC-1258 controler IP settings and the ADSL router(Linksys).
If I select DHCP (which I would prefer) as soon as I get a break in the ISP connectivity I almost instantly get the DNS error desribed below on the controler RRC-1258. No matter what DNS server has been selected.

If I select a fixed IP address and an external DNS server, Google etc, I still get the error:

DNS status Error, failed to resolve xxxxxxx.ham-radio-op.net!

Resetting the RRC-1258 several times does not cure the problem - however removing its power for 10 mins does. So my original thoughts concerning DNS caches remain

John G4SWX

Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #5 on: 2011-05-16, 10:15:26 »
I looked at the configuration between the RRC-1258 controler IP settings and the ADSL router(Linksys).
If I select DHCP (which I would prefer) as soon as I get a break in the ISP connectivity I almost instantly get the DNS error desribed below on the controler RRC-1258. No matter what DNS server has been selected.

If I select a fixed IP address and an external DNS server, Google etc, I still get the error:

DNS status Error, failed to resolve xxxxxxx.ham-radio-op.net!

Resetting the RRC-1258 several times does not cure the problem - however removing its power for 10 mins does. So my original thoughts concerning DNS caches remain

John G4SWX
How long is a "break in the ISP connectivity"? And when the "DNS Status Error.." occurs, does it remain as "Error" not only for the duration of the "break", but also after the connection has been restored?

Also, do you mean that you don't have NAT at the router, so that the control RRC gets a new (external) IP address after each break(if on DHCP)?
Always include type of hard/software and version when asking for support.

g4swx

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Re: RRC-1258 DNS Cache
« Reply #6 on: 2011-05-16, 16:09:37 »
> How long is a "break in the ISP connectivity"?
Can be as little as 20secs but mostly no more than 2 mins
>And when the "DNS Status Error.." occurs, does it remain as "Error" not only for the duration of >the "break", but also after the connection has been restored?
That is the point I am attempting to make, an interuption during the break is obvious but it remains after the break is restoration. Disruption of the DSL connection causes the RRC to get hung in a mode where a simple 'reset' will not sort it out, this can remain for up to several hours (at which power down everything). Removing the power from the RRC for ~ 10 mins and then restarting cures the problem.
>Also, do you mean that you don't have NAT at the router, so that the control RRC gets a new
>(external) IP address after each break(if on DHCP)?
Yes I do use NAT and DHCP at the router so that the RRC should, in theory, see nothing of the external network. Yet it seems to be aware of the connectivity failure.
That is why I asked about the DNS cache. Perhaps I should be asking about the cache of all of the network credentials as I guess that is what gets removed in a 10min power down.
73
John G4SWX

Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #7 on: 2011-05-16, 16:51:11 »
There is a DNS cache in the RRC, but it would, at least in theory, work in the opposite way. That is, it would allow the RRC to resolve a given host name "internally" the 2nd time and forward. So it should not give DNS Error in that case as it would succeed in resolving for ex. the radio RRC's host name.

I could imaging a situation where the RRC gets "confused" if something at the router side gave it a new IP address etc when on DHCP and the RRC is not restarted, but I can't see how it would take say 10 minutes of disconnected power in order to fix it. A normal simple reset should be more than enough since it wipes out every possible memory cache as well as ask the DHCP server for a new IP address.

Also, since your router uses NAT then I don't see why it wouldn't be possible for the RRC to have the same assigned IP address it got when starting up regardless of the ADSL status? As you write, the RRC should not see anything of the external network, besides the obvious that the RRC won't be able to communicate with the external network during a ADSL disruption.
Always include type of hard/software and version when asking for support.

g4swx

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Re: RRC-1258 DNS Cache
« Reply #8 on: 2011-05-19, 23:06:57 »
It is still hapenning, at least once per day. I have set a fixed IP 192.168.1.125 for the control RRC so it is on the same subnet but free from DHCP issues at the router.
When the blip on the ISP side occurs I usually note a different  DHCP (ISP) address on the router WAN side. But as I am running a fixed IP for the RRC on the LAN side (Ethernet not wireless) this should not matter.
The DNS status then goes to error - failed to resolve
With power applied I have rebooted 4 or 5 times - the RRC first comes up DNS status : unknown
but on attempting a connection it fails with the DNS stutus in error - failed to resolve....
Powering down for a minute or so is not enought - when attempting a connection it fails with the DNS stutus in error - failed to resolve....
After about 8-10 mins of no power the RRC boots-up, initially with DNS status: unknown but after about 30 secs the status reports Ok!
I am running software 2.35 - would an update help? or is it possible that have I problem with MAC caching on the router(Linksys) rather than caching on the RRC?
However if it was a router issue I would expect to have an issue with my PCs which I do not, even when they are on DHCP.
73
John G4SWX

Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #9 on: 2011-05-20, 09:51:50 »
I don't think an update would do any good since this isn't a common/known issue with the software.

Can you try connecting the RRC to another router/switch(for ex. a switch being between the existing and the RRC)? We have seen situations with differences in behaviour between for ex the RRC and another network equipment, so I would not rule of the possibility of a "unlucky" combination of your router and the RRC. One customer in Norway had to change router/modem in order to get it working.

What is "Eth-type" on the page "IP Settings"? You could try change between "Auto" and "Auto, prefer 10".
Always include type of hard/software and version when asking for support.

g4swx

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Re: RRC-1258 DNS Cache
« Reply #10 on: 2011-05-31, 21:27:04 »
OK, - I think that I have found a way around the problem:
I had set up an IP configuration on the control RRC that included; IP address, subnet mask, gateway address and external DNS server. Howevever if I delete all of these and set the IP setting to DHCP the problem goes away. ie when the ADSL at the control station drops momentarily, restores but with another IP address from the ISP DHCP pool the RRC continues, after the obvious drop-out, to work. However if I set an external DNS server address and the ADSL drops, the RRC ges into the "DNS Status Error.." condition and the only cure is to power down the RRC for ~ 10mins.
What is curious is that I have changed the ADSL router from Linksys to 2Wire and can repeat the problem and the work-around.
So the question comes back to one of what network information gets cached in the RRC as it should not be aware of the router NAT session?
73
John G4SWX

Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #11 on: 2011-06-01, 09:59:32 »
This thing you describe is still not possible to understand. DHCP or not DHCP, when the RRC is behind a NAT router it should not cease functioning after in your case a disrupt in the external network(ADSL). The IP stack we are using is not written by ourselves, which makes it hard to answer about what caching it might do or not. Also as far as I know you are the only one experiencing something this strange, which should mean that it can't be very common. I have a Webswitch with a static address IP at home, which uses the same IP stack and network hardware as the RRC do, and it always resume operation after ADSL failure(which as been quite often lately)

When using DHCP, did it maintain the same IP during and after the ADSL disruption? ("Info " page). If DHCP seems to work for you, why not use that? If you tell your router to assign the RRC's MAC the same IP every time, then you will find it easily too.
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g4swx

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Re: RRC-1258 DNS Cache
« Reply #12 on: 2011-06-02, 21:44:32 »
> This thing you describe is still not possible to understand. DHCP or not DHCP, when the RRC is behind > a NAT router it should not cease functioning after in your case a disrupt in the external network
> (ADSL).

I would tend to agree on the theory but it will be dependant upon what the IP stack puts into cache and how it manages its (internal network) DHCP handshake. It seems as though every other device on my network, PCs(Win + LINUX), IPhones, Internet Radio, 2 x STB etc, fixed or DHCP has no problems with the router (Cisco- Linksys) of the loss of ADSL + change of supplier IP. Even changing the router from Linksys to 2Wire does not resolve it.

Using DHCP for the RRC controller is not really acceptable as if there is any issue, and there are several every day) I first have to hunt in the router's DHCP table and guess what IP it has.

The problem is probably triggered more often as in the UK the ISPs circulate their IP addresses, from a large pool of quite different /24s on the DHCP servers. That means that if your router drops its PPP session for whatever reason it will almost always gain a new external address often from a very different netblock. This means that the router NAT table has to be refreshed with each new request from a downstream device. It seems that the RRC IP stack does not behave in the same way as all of the other devices on my network. It does, like all other devices retain the same (internal) IP address after such a change. Perhaps it is a quirk of the embedded stack and the caching of the DHCP credentials, in particular when an 'external' DNS server has been selected. However a 10 (not 5!) minute power-down will reset things.
If I have time I will capture 'normal' and 'lock-up' traffic with Wireshark.
73
John G4SWX

Jan (Microbit)

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Re: RRC-1258 DNS Cache
« Reply #13 on: 2011-06-07, 10:16:02 »
I don't understand why you talk about DHCP and its handshake as being part of the problem? I thought that by using DHCP it works? Then how can DHCP handshake etc have something to to with it? But I agree that there seem to be something different with the RRC since it's the only device which gets problems.

I suggested you set up your RRC to use DHCP and your router so that it assigns the RRC the same(known) IP every time, but you still say you will have to "hunt in the router's DHCP table and guess what IP it has." Does that mean that your router doesn't support assigning a particularly network device a give IP using DHCP?

Capturing 'normal' and 'lock-up' traffic with Wireshark would be great!
Always include type of hard/software and version when asking for support.

g4swx

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Re: RRC-1258 DNS Cache
« Reply #14 on: 2011-07-22, 13:29:17 »
Sorry for the delay - I got my ADSL drop-outs fixed and this became less of an issue.
However I have now captured all of the packets in the failure mode and although I had thought it was a DNS cache issue in the RRC1258 it is the the router holding onto the NAT session for the DNS look-up! Much as you suggested this is obviously a router bug but with this particular router Linksys WAG300N it only seems to impact DNS. It also times out in about 5 mins.....
So; the DSL drops, router gains new external IP address whilst still 'hot', attempt to connect RRC-1258, DNS look-up fails........ Checked this by configuring a PC in a similar manner.
Complete fix = trash the Linksys router. :-[
Thank you for your help :)
73
John G4SWX