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Cisco Bug: CSCuj63079 - 7937 discards default GW ARP response &resets when high ARP on data vlan

Last Modified

Nov 27, 2020

Products (1)

  • Cisco SIP IP Phone Software

Known Affected Releases

1.4(4) 1.4(5)

Description (partial)

7937 conference phone unregisters and registers back. 7937 might unregister while on a call or when idle.

High ARP traffic in the data VLAN assigned for the switch port  in which the phone is connected

Conference Phones Cisco 7937 unregisters and registers when there is ARP flooding in the data VLAN.

- 7937 switchport has both data and voice vlans configured
- Large number of ARPs to broadcast address, on data vlan
- 7937's threshold is 50 ARP packets / sec
- If threshold is exceeded, 7937 discards the subsequent ARP packets, irrespective if it was to broadcast address or destined to its address
- ARP cache on 7937 phone is 10 minutes
- After ARP cache timeout, 7937 ARPs for default GW address
- Default GW responds with its address
- However, due to high ARP on data vlan, 7937 discards the ARP response from default GW on voice vlan
- 7937 doesn't know the next hop to send KeepAlive packet to CUCM, to stay registered
- ARP request and response process loops around
- If ARP response doesn't get processed by the 7937 by 2 KeepAlive intervals (50-60 seconds), CUCM or the 7937 closes the TCP session and the 7937 goes into a reset.
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