This article created based on the customer's case which report that switch does not send ARP, even there is L3 traffic and switch doesn’t have ARP information. Expected behaviour on L3 switch is to send ARP to resolve the mac address information of end host, but customer device does not work as expected with below symptom.
Symptoms
Switch didn’t send ARP even there is L3 traffic to end host, and switch have no ARP information of end host.
Cause of the problem
If switch’s arp pending entries reach to the maximum of pending entries, then switch cannot send ARP request.
CORE1.10 # show iparp
VR Destination Mac Age Static VLAN VID Port
VR-Default 192.168.11.1 00:04:96:37:3b:ae 0 NO v11 3010 3:1
Dynamic Entries : 1 Static Entries : 0
Pending Entries : 256
In Request : 0 In Response : 1
Out Request : 9121 Out Response : 0
Failed Requests : 1290
Proxy Answered : 0
Rx Error : 0 Dup IP Addr : 0.0.0.0
Rejected Count : Rejected IP :
Rejected Port : Rejected I/F :
Max ARP entries : 8192 Max ARP pending entries : 256
ARP address check: Enabled ARP refresh : Enabled
Timeout : 20 minutes ARP Sender-Mac Learning : Disabled
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In Request The number of ARP request packets received (by this VR or VRF).
In Response The number of ARP reply packets received (by this VR or VRF).
Max ARP entries Maximum ARP table size for the VR or VRF (each VR has its own ARP table).
Max ARP pending entries Maximum number of incomplete (pending) ARP entries allowed in the table.
Out Request The number of ARP request packets sent (by this VR or VRF).
Out Response The number of ARP reply packets sent (by this VR or VRF).
Pending entries The number of sent ARP requests that have not yet received a response.
Proxy Answered The number of ARP requests answered by the ARP proxy.
RX Error The number of incorrect ARP request and reply packets received. The malformed packets include the following errors: incorrect ARP op code, hardware address type is not Ethernet, the protocol address is not IP, and similar errors.
Static entries The number of configured (static ARP) entries in the table.
Rejected Count The number of rejected ARP request packets.
Rejected I/F The VLAN on which the last rejected ARP request packet arrived.
Rejected IP The source address for the last rejected ARP request. An example reason for an ARP request packet to be rejected is if the source address of the packet is not in the subnet.
Rejected Port The port on which the last rejected ARP request packet arrived.
Timeout Timeout value for a dynamic (learned) ARP entry.
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Resolution
Increase max_pending_entries by configuring “configure iparp max_pending_entries”
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