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Cisco Bug: CSCur38790 - Interface bouncing when DHCP is configured, but no cable is plugged in

Last Modified

Sep 14, 2019

Products (11)

  • Cisco 5900 Series Embedded Services Routers
  • Cisco 2951 Integrated Services Router
  • Cisco 5915 Embedded Service Router
  • Cisco 2911 Integrated Services Router
  • Cisco 3925E Integrated Services Router
  • Cisco 3945E Integrated Services Router
  • Cisco 2901 Integrated Services Router
  • Cisco 5940 Embedded Services Router
  • Cisco 3925 Integrated Services Router
  • Cisco 2921 Integrated Services Router
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Known Affected Releases

15.2(4)GC

Description (partial)

Symptom:
When a cisco 5921 ESR interface whose line protocol is in down state(peer not connected or peer in down state), is configured to receive an IP address via DHCP, the interface may bounce up and down forever.

Oct 14 21:18:12 router 208: Oct 14 21:18:11.678: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to down
Oct 14 21:18:14 router 209: Oct 14 21:18:13.680: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up
Oct 14 21:18:22 router 211: Oct 14 21:18:21.678: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to down
Oct 14 21:18:24 router 212: Oct 14 21:18:23.680: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up
Oct 14 21:18:32 router 213: Oct 14 21:18:31.678: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to down
Oct 14 21:18:34 router 214: Oct 14 21:18:33.680: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up

SWROPTIONS example - IOS interface e0/0 mapped to linux eth0
[interface]
linux=eth0
ios=e0/0
type=raw
promiscuous=true
monitor-state=true

IOS - Interface config:
interface Ethernet0/0
ip address dhcp
no shut

This could be seen in all IOS versions that support c5921 platform.

Conditions:
Interface flapping occurs only in the below conditions:

1.  When the linux interface is not connected to any peer,  "ip address dhcp" and "no shut" commands are configured in this order.

interface Ethernet0/0
ip address dhcp
no shut


2.  When the linux interface is not connected to any peer,  "no shut" and "ip address dhcp" commands are configured in immediate succession.

interface Ethernet0/0
no shut
ip address dhcp


3.  When the linux interface is connected to a peer and IOS interface is also in "up" state, configure ip address dhcp and shut the peer interface.

c5921
interface Ethernet0/0
ip address dhcp

Peer
interface Ethernet0/0
shut

5921 interface will bounce until the neighbor becomes up.
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Bug Details Include

  • Full Description (including symptoms, conditions and workarounds)
  • Status
  • Severity
  • Known Fixed Releases
  • Related Community Discussions
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