Bug 610236 - [4u8] Bonding in ALB mode sends ARP in loop
Summary: [4u8] Bonding in ALB mode sends ARP in loop
Alias: None
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: kernel
Version: 4.8
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Flavio Leitner
QA Contact: Liang Zheng
Depends On: 610234 610237
Blocks: 629239
TreeView+ depends on / blocked
Reported: 2010-07-01 19:58 UTC by Flavio Leitner
Modified: 2013-07-29 00:56 UTC (History)
6 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of: 610234
Last Closed: 2011-02-16 15:39:34 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2011:0263 0 normal SHIPPED_LIVE Important: Red Hat Enterprise Linux 4.9 kernel security and bug fix update 2011-02-16 15:14:55 UTC

Description Flavio Leitner 2010-07-01 19:58:50 UTC
+++ This bug was initially created as a clone of Bug #610234 +++

Description of problem:
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

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.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
Just ping one system from another with both running bonding in ALB mode and you can see the ARP being sent each 2 seconds between them.
Actual results:
It is impossible for a backup system to take over the IP address when there are other systems sending wrong ARP packets poisoning the network.

Expected results:
Don't send unneeded ARP packets

Additional info:
The patch is available upstream:

The patch is backported for RHEL5 and we are waiting for testing results.

Comment 1 Andy Gospodarek 2010-07-16 17:31:49 UTC
Flavio, you did the leg work on this and you earned the internal credit too.  Please post this when you get positive feedback.

Comment 2 RHEL Program Management 2010-07-16 17:39:04 UTC
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release.  Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products.  This request is not yet committed for inclusion in an Update

Comment 6 Vivek Goyal 2010-08-20 19:48:12 UTC
Committed in 89.32.EL . RPMS are available at http://people.redhat.com/vgoyal/rhel4/

Comment 11 errata-xmlrpc 2011-02-16 15:39:34 UTC
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


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