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authorFlavio Leitner <fleitner@redhat.com>2010-06-29 08:24:39 +0000
committerDavid S. Miller <davem@davemloft.net>2010-06-30 13:51:11 -0700
commit42d782ac1bef7cbcdf05b857731345c6e8149f90 (patch)
treea832741c37a71797220914f360b454dcca1fff18 /Documentation/RCU/rculist_nulls.txt
parentdd1589a431e90f9ff587e640c67101a565e52bba (diff)
bonding: check if clients MAC addr has changed
When two systems using bonding devices in adaptive load balancing (ALB) communicates with each other, an endless ping-pong of ARP replies starts between these two systems. What happens? In the ALB mode, bonding driver keeps track of each client connected in a hash table, so it can do the receive load balancing (RLB). This hash table is updated when an ARP reply is received, then it scans for the client entry, updates its MAC address and flag it to be announced later. Therefore, two seconds later, the alb monitor runs and send for each updated client entry two ARP replies updating this specific client. The same process happens on the receiving system, causing the endless ping-pong of arp replies. See more information including the relevant functions below: System 1 System 2 bond0 bond0 ping <system2> ARP request ---------> <--------- ARP reply +->rlb_arp_recv <---------------------+ <--- loop begins | rlb_update_entry_from_arp | | client_info->ntt = 1; | | bond_info->rx_ntt = 1; | | | | <communication succeed> | | | | bond_alb_monitor | | rlb_update_rx_clients | | rlb_update_client | | arp_create(ARPOP_REPLY) | | send ARP reply --------------> V | send ARP reply --------------> | rlb_arp_recv | rlb_update_entry_from_arp | client_info->ntt = 1; | bond_info->rx_ntt = 1; | < snipped, same as in system 1> +------- <-------------- send ARP reply <-------------- send ARP reply Besides the unneeded networking traffic, this loop breaks a cluster because a backup system can't take over the IP address. There is always one system sending an ARP reply poisoning the network. This patch fixes the problem adding a check for the MAC address before updating it. Thus, if the MAC address didn't change, there is no need to update neither to announce it later. Signed-off-by: Flavio Leitner <fleitner@redhat.com> Signed-off-by: Jay Vosburgh <fubar@us.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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