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Old 11th March 2013
kbeaucha kbeaucha is offline
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Default Ethernet port becomes unresponsive - troubleshooting suggestions

Hello:

I have a remote site where I'm having a problem with the OpenBSD network gateway I'm using there. This site is one of five that are all configured basically the same, and this site has been in service for many years. What we thought was a minor change has apparently caused a new problem.

The remote site's gateway forwards packets between its upstream port and its local network port. Most traffic comes in on enc0, because the gateway is one end of a point-to-point VPN tunnel set up using ipsec, but the upstream port is pingable and permits ssh logins.

For the longest time a Soekris 4801 ran the tunnel flawlessly.

A recent change put a new embedded controller behind this gateway. From the local network, you can log into the controller by telneting to port 1400, and the same port is used to push data back to a Macintosh on our main campus through the tunnel.

No changes were made to our remote ruleset to accommodate this move.

After we added this controller and Mac connection, we began to experience times when the upstream port at the remote site would become unresponsive. Data wasn't traversing the tunnel for anything behind the Soekris; I believe the tunnel was being dropped. The upstream port would not allow ssh logins and would not respond to pings.

Power-cycling the Soekris would bring everything back.

To eliminate the possibility that the Soekris was the cause, we replaced it with a (faster) PC Engines Alix unit. The problems seemed to go away for over a year, until last week, when the tunnel dropped again.

Due to some other problems I wasn't able to log into the Alix's serial port, but the upstream (and local network) ports still had link, and the admin for the switch that the upstream port was plugged into said he could see link and get the MAC address of the gateway. I am open to suggestions on what to look for if this should occur again to help resolve the problem.


tia
kmb

Last edited by kbeaucha; 11th March 2013 at 08:09 PM. Reason: Add some details on state of upstream port from other admin
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Old 11th March 2013
ocicat ocicat is offline
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..and the version of OpenBSD used is what?
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Old 12th March 2013
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jggimi jggimi is online now
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Quote:
Originally Posted by kbeaucha View Post
...After we added this controller and Mac connection, we began to experience times when the upstream port at the remote site would become unresponsive. Data wasn't traversing the tunnel for anything behind the Soekris; I believe the tunnel was being dropped. The upstream port would not allow ssh logins and would not respond to pings.
Your problem reflects something more than an IPSec tunnel being dropped. Your non-VPN communications -- ping and ssh -- were non-functional.
Quote:
Power-cycling the Soekris would bring everything back.
Was there ever an admin monitoring the console at this time? For example, the OS may have been functional but the NIC was not, or the OS may have panicked and dropped into ddb(4), or the OS may have been hung. Without a console (and an admin, local or remote) you would not be able to determine which of these three possibilities was occurring.
Quote:
To eliminate the possibility that the Soekris was the cause, we replaced it with a (faster) PC Engines Alix unit. The problems seemed to go away for over a year, until last week, when the tunnel dropped again.

Due to some other problems I wasn't able to log into the Alix's serial port, but the upstream (and local network) ports still had link, and the admin for the switch that the upstream port was plugged into said he could see link and get the MAC address of the gateway.
Do you also lose ping response on the Alix? It's not completely clear if that's the case.

I am not sure what you mean by "link" -- if you are describing status lights on Ethernet hardware (switches / hubs) these have various meanings depending on NIC manufacturer but are related to physical connectivity and not to data transfer. In the event of a software failure (OS hang/ OS panic / NIC bug) electrical connections would not necessarily be severed.

I know enough about Ethernet to use it and administer it. I'm not a NIC hardware expert, nor a NIC driver writer. With that disclaimer out of the way, I think it is perfectly reasonable for Ethernet NICs to manage traffic independent of the OS, to ignore (or pass on, depending on the type of Ethernet) non-broadcast Ethernet frames destined for MAC addresses other than its own. In like manner, I assume a NIC could respond appropriately to Ethernet frames that query for its MAC address. This is different than responding to ARP requests for IP address / MAC address resolution.
Quote:
I am open to suggestions on what to look for if this should occur again to help resolve the problem.
  1. Plug in a console, for use by you or your admin for the switch. Use it when this occurs to determine if the OS is still operating, the OS has crashed, or the OS has panicked.
  2. Monitor ongoing operation, while things are going well. Pay special attention to free mbufs -- if you run out of message buffers, your network stack will stop moving data. You can see current mbuf usage with the -m option to netstat. Script something that notifies you if you start running out of mbuf capacity.
  3. Review system logs from at the time of the problem -- in the event of a hang/crash, these probably will not aid you. In the event you were logging to a remote syslog server, these will probably not aid you. But if you are/were logging to /var/log locally, inspect /var/log/messages* files for any messages at the time the errors occurred. In the event mbuf shortages were the cause, look for "mcplimit limit reached" messages.
Quote:
Originally Posted by ocicat View Post
..and the version of OpenBSD used is what?
That too, is another good question. Last you mentioned it, in May of 2012, your systems were running 5.0.

Last edited by jggimi; 12th March 2013 at 12:32 AM. Reason: typos
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Old 15th March 2013
kbeaucha kbeaucha is offline
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I tried to log into the Alix, but was unable to due to problems unrelated to the Alix itself (another story). I opted for the power cycle because this was an after-hours call and I wanted to restore service as quickly as possible.

I do lose ping response on the Alix. The admin for the upstream switch logged into his Cisco and checked the status on the port our Alix plugs into. It was the Cisco that reported a "link"ed device on the appropriate port and its (the Alix's) MAC address (although I'm uncertain if the Cisco just had that information cached).

As you suspect, the version running is 5.0

I'm in the process of resolving the console availability issue.

When monitoring mbufs (netstat -m), is there something specific I should look for, or just usage over time?

Thanks for the suggestions.

kmb
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Old 15th March 2013
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Quote:
When monitoring mbufs (netstat -m), is there something specific I should look for, or just usage over time?
Take a look at the netstat output. You will see significant details of mbuf use - including types of usage and a list of mbufs consumed by size, and counts of requests cancelled or deferred.

But you will also see an output line showing a percentage in use. I recommend a cron job that parses that line for the percentage, and notifies you if it exceeds some threshold you set -- for example, choose a threshold of 50% or 75%.

While writing that cron job, you might also want to look at consumption of PF states in that remote router-- the default is 10,000, and while a small office firewall should not exceed that, perhaps there is a problem causing excess state table consumption. See the pfctl(8) man page, and option -s info.
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