From: Nitin Yadav Sent: Thursday, September 27, 2012 12:16 PM To: 'netdev@vger.kernel.org' Subject: RE: Linux Kernel not responding to ARP requests Hi All, I am facing loss of connectivity between Linux system (2.6.18 kernel) & Cisco switch (6509) when HSRP is enabled. The Cisco switches (STAND BY) ARP queue were flushed and new MAC address were requests, but the kernel did not answer to this requests. After investigation I found out that the Cisco switch (STAND BY) is flushing the MAC address of the kernel port. Based on Cisco they are flush the MAC address of inactive port every 8 minutes. A small note about the protocol (HSRP):- Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway, and has been described in detail in RFC 2281. The protocol establishes a framework between network routers in order to achieve default gateway failover if the primary gateway becomes inaccessible,[1] in close association with a rapid-converging routing protocol like EIGRP or OSPF. By multicasting packets, HSRP sends its hello messages to the multicast address 224.0.0.2 (all routers) for version 1, or 224.0.0.102 for version 2[2], using UDP port 1985, to other HSRP-enabled routers, defining priority between the routers. The primary router with the highest configured priority will act as a virtual router with a pre-defined gateway IP address and will respond to the ARP request from machines connected to the LAN with the MAC address 0000.0c07.acXX where XX is the group ID in hex. If the primary router should fail, the router with the next-highest priority would take over the gateway IP address and answer ARP requests with the same mac address, thus achieving transparent default gateway fail-over. A HSRP Basics Simulation visualizes Active/Standby election and link failover with Hello, Coup, ARP Reply packets and timers. My queries :- Is there any way Kernel is dropping the ARP requests (from the Stand by Router to the Kernel)? If it's not dropping, is there any other reason for not replying to ARP? Thanks! Nitin Yadav Information transmitted by this e-mail is proprietary to MphasiS, its associated companies and/ or its customers and is intended for use only by the individual or entity to which it is addressed, and may contain information that is privileged, confidential or exempt from disclosure under applicable law. If you are not the intended recipient or it appears that this mail has been forwarded to you without proper authority, you are notified that any use or dissemination of this information in any manner is strictly prohibited. In such cases, please notify us immediately at mailmaster@mphasis.com and delete this mail from your records.