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ARP problem ?

Hello all, 

I have a very strange problem. I have 2 Cisco 6500 switches with hsrp . I have created VLAN 400 with no svi . In this switches i also have 2 trunk ports that im connecting a vmware server that has a team interface this 2 trunk ports and a virtual switch. Behing this virtual switch it is a virtual machine in VLAN 400 with ip

In cisco 6500 i have connect another cisco router into an access port in vlan 400 and i have him an ip . My problem is that Virtual machine can ping and communicate with this router but if no traffic pass for a few minutes , the router lose connectivity with the virtual machine. If i initiate a ping from the VM to the router then connectivity is restored. In router if i give a show arp i also see that i cannot found the mac of the VM . It appears again when i initiate ping from vm to router.

Any ideas ? 

Thanks a lot


I think default value for arp

I think default value for arp cache timeout is 4 hours on Cisco routers. Can you check what the arp cache timeout value is on this router? 

There is a work around of creating a static arp on the router for the vm so it will never timeout.


Hello and thanks for the

Hello and thanks for the answer , 

I thing that the arp cache timeout is the default which is 240 minutes . But the problem appears after 10-15 minutes without any traffic passing . Then i send a ping and connectivity is restored. 

I have thought also this workaround but im searching first for a solution or any ideas . 

Thanks again


Can you check what the arp

Can you check what the arp timeout value is on the router's interface that's connected to 6500? Router shouldn't flush a dynamic arp entry  before the arp cache time out value unless IOS is corrupted.

sh int f0/0
FastEthernet0/0 is up, line protocol is up
  Hardware is DEC21140, address is ca07.4378.0000 (bia ca07.4378.0000)
  Internet address is
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Half-duplex, 100Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:02, output 00:00:09, output hang never
  Last clearing of "show interface" counters never


Arp timeout is set to 4 hours

Arp timeout is set to 4 hours . I manage to solve the issue by using a new VLAN with a subnet with SVI. Previous VLAN has no SVI . Now all seems to work without any problems. Off course it is still a mystery this behavior 


Its not a Cisco issue,

Its not a Cisco issue, Vmotion VM to new host (if ESX) and check if the issue persists.


I agree with Vitesh that

I agree with Hitesh that there seems to be an issue on the VM, but that shouldn't affect the arp table on router. That still remains a mystery.


Hello Hitech , 

Hello Hitech , 

I have already try this and it has the same behavior . 

Thanks for your help

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