IP ARP: ignored gratuitous arp on C3750

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Jul 15th, 2009
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Hi,


We have a stack of 3 C3750 switches with

IOS version 122-46.SE and i keep getting the below error:


IP ARP: ignored gratuitous arp src <SRC-IP> <SRC-MAC>, dst <DST-MAC> <SW-MAC>, interface Vlan1


On this stack we have some clustering solutions e.g AIX HACMP and CheckPoint ClusterXL. At some point we also had an issue with cluster failover. A cluster IP is failing over between the two nodes but the MAC address used is the one that each node has and not a virtual one. After i used the ip sticky-arp command the problem fixed.


It could be that the two issues are not related but since the clusters normally send GARPs to notify the network to update the ARP tables it might make sense


Your feedback would be appreciated.#


./G


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Giuseppe Larosa Thu, 07/16/2009 - 01:19
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Hello George,

your understanding is correct what you see might has an impact.


just verify if the source ip is in the expected ip subnet associated to vlan1 this check is performed in any case.


if the Garp has a correct ip address you may need to enable reception of these Garp on device.


Hope to help

Giuseppe



g-georgiou Thu, 07/16/2009 - 02:12
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Hi Giuseppe,


Thanks for the quick response. The stange thing is that the GARP ignored msg is still appearing even after i used the commnand ip sticky-arp. The src IP is in the expected subnet in Vlan1. Interface Vlan1 is only used for management. By default i guess every OS allows the reception of GARP. I guess that the switch ignores the GARP because it is a broadcast and the switch does not like it. I still believe that the the GARP is not related to the sticky MAC. Unfortunately Cisco Doc is poor for this issue :(.


./G

Giuseppe Larosa Thu, 07/16/2009 - 02:22
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Hello George,

Garp needs to have a broadcast destination


if vlan1 is used only for management these messages could be unrelated to the real issue you are facing but they indicate the device can ignore them also on other vlans.


Sticky mac addresses are another matter but they can be part of the problem


Hope to help

Giuseppe


g-georgiou Thu, 07/16/2009 - 02:42
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Giuseppe,


This is exaclty my understanding. Some times it takes another opinion to make you feel more confident :).


Did you ran into this kind of issue with the sticky-arp? Is there any debug for this or log? I did not manage to find anything. It seems very rare problem.


./G

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