According to my ISP, our occasional internet outages are do to a router configuration problem. They say the router must RPing the ISP regularly. Failure to do so in 4 hours results in outgoing and incoming internet loss. According to their logs the RPing is occurring randomly. And on some occasions, more than 4 hours apart.

The router is Cisco 800 Series.

What is RPing? Is it related to RDMA? How do I configure the RPinging? I attempted to google but obviously I am using the wrong terminology as the results were unhelpful.

  • Get more information from your ISP, ask them for sample config for Cisco 800 series router.
    – Abu Zaid
    Mar 10 at 16:39
  • @AbuZaid ISP clarified it is the "ARPing" that did not trigger for over 4 hours. No sample configuration available for any router. The rep went on to say that any activity on the router at all, incoming or outgoing traffic would keep the connection alive. However, we had thousands of connections per hour for the 4 hours leading up to the drop. We have escalated the issue. I should be getting a call from an ISP engineer.
    – Dorothy
    Mar 10 at 18:01
  • That seems to be inactivity timer, which some ISPs deploy to terminate idle PPP sessions. If there was traffic, then it shouldn't have been triggered. Could be another issue. To prevent idle timeout, you can setup sla monitor, that would ping a device, such as Google DNS server every few minutes. But in your case, it looks like, it is not needed.
    – Abu Zaid
    Mar 11 at 9:43

Reading Monitoring and Maintaining ARP Information Documentation was helpful to understand ARP, ARPing and ARP Caching.

ARP was developed to enable communications on an internetwork...Routers and Layer 3 switches need ARP to map IP addresses to MAC hardware addresses so that IP packets can be sent across networks.

...To minimize broadcasts and limit wasteful use of network resources, ARP caching was implemented....the ARP subsystem refreshes dynamic ARP entries periodically (as configured or every four hours by default) so that the ARP table reflects any changed, aged-out, or removed dynamic routes.

I ran show ip arp to see a list of ARPs cached, aged time and Interface name. I then ran show intefaces and confirmed that the ARP Timeout is at the default of 4 hours.

However according to my ISP the ARPings or ARP refresh requests are being received by them at varying times. Usually just under 4 hours but occasionally just over 4 hours (when the connection is dropped). For the last two connection drops, time between pings was 4:10 and 4:15.

I read on a Cisco Community Post: ARP cache timeout on Cisco routers:

Richard Burts "the request to refresh the arp entry is generated near the end of the arp lifetime...Cisco adds a variable amount of time in determining when to generate the arp request. The logic is that they want to avoid synchronization of the arp entries. If we have flushed all the entries in the table and re-learned all the entries at approximately the same time then when they are about to expire we do not want to flush them all at the same time

paul driver's testing revealed what Richard Burts further described: "while the arp timeout was set to one hour the requests to refresh the entries were all longer than an hour. So the variability that Cisco adds can be longer than the time...the bottom line is that the arp timeout is not a precise timer but an approximation of when the entries will be refreshed or be purged from the table."

It seams the best solution at this point is to reduce the ARP Timeout on my router.

cisco(config-if)#int f0/0
cisco(config-if)#arp timeout 10800

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