Router randomly losing connection to the internet

[Ron Reid]

I have an issue happening on two of my routers different models and IOS versions.

On two if the sites I administer, the ISP has presented an internet connection on Ethernet provided a public IP address for the router and a gateway address. The architecture is similar in both scenarios so I will describe one.

The ISP ethernet connection has been connected to a L2 Vlan on a WS-C2960X-24PS-L switch. The 897VA router WAN port (Gi8) has been connected to the same vlan on the same switch. Switch port interface config as follows:

interface GigabitEthernet1/0/23
description *Connection to router
switchport access vlan 999
switchport mode access

!

interface GigabitEthernet1/0/24
description *Connection to ISP
switchport access vlan 999
switchport mode access

897VA Router Gi8 connection as follows:

ip vrf Internet
rd 0:2

!

interface GigabitEthernet8
ip vrf forwarding Internet
ip address 88.89.90.174 255.255.255.252
duplex auto
speed auto

!

ip route vrf Internet 0.0.0.0 0.0.0.0 88.89.90.173

This connects, and works for a few days and then randomly loses connection.

When the service has failed and I do an arp check on the router I get the following result:

sh ip arp vrf Internet
Protocol Address Age (min) Hardware Addr Type Interface
Internet 88.89.90.173 0 Incomplete
Internet 88.89.90.174 - f80b.cbad.c5aa ARPA GigabitEthernet8

There are no errors on the router WAN port, the interface is up up, but it doesn't seem to be communicating with the switch L2 LAN.

The mac address for the ISP gateway address can be seen on the switchport interface Gi1/0/24 if query the mac address with the exec command "show mac address-table interface Gi1/0/24"

A reload of the 897va router resolves the problem and brings the service up again so there is no issue with the ISP, the issue appears to be on the router.

Has anyone experienced this issue. I'm not sure where to go next with the troubleshooting.

[Daniele Giordano]

Hi, during the issue you can see the mac address of provider gateway on the switch.

But, what happen if you try to clear mac-address on the switch?

Is the mac still present?

If nom check with the provider.

If yes, what happen if you try 'clear ip arp vrf Internet' ?

If the connection is restored, can you try to reduce the arp timeout on the router?

Regards.

[Ron Reid]

I haven't tried any of those options specifically, what I have done is a shut and no shut on the switchport interface to the ISP, as well as the WAN port of the router. This doesn't restore the service.

With the shut/no shut on the switchport interface to the ISP the mac address does re-establish itself on the interface. A query on the switch mac address table for that vlan only reveals the ISP mac address.

[Richard Burts]

When you see an entry in the arp table that is incomplete it is a sign that the router has sent an arp request for the ISP but did not receive a response. Am I correct in understanding that while this problem is happening that you looked in the mac address table on the switch and did not see an entry for the router mac address?

And am I correct in understanding that while the problem is happening that you have tried shut and no shut on the switch interface connecting to the router? And that this did not solve the issue?

HTH

Rick

[Ron Reid]

Yes that sums it up. The problem appears to be on the router side rather than the switch side because rebooting the router restores the service.

It's difficult to troubleshoot because the problem is random and with a known workaround, there's business pressure to get the connection up so I don't get much time to work on the issue.

[Richard Burts]

Thanks for the update. I understand business pressure to restore connectivity quickly. Management has a choice to make. Either they accept that periodically they will have interruptions on an ongoing basis or they allow some time for troubleshooting. If they allow some time to troubleshoot we may be able to offer some assistance. If they do not allow time then there is nothing further we can do from the community.

HTH

Rick

[Daniele Giordano]

As suggestedm can you check spanning tree issue?

Can you check the port status of the switch and router during the problem? Use show spann summary.

What IOS version is installed on the switch?

Can you try a fresh wan?

Could be a bug fixed in a recent firmware but it's only an supposition.

Regards.

[paul driver]

Hello

interface range GigabitEthernet1/0/23 -24
spanning-tree portfast
exit