netdev - Bonding in active-backup mode with arp monitoring on Xen

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Message-Id: <47253487.3010909@nb.jp.nec.com>
Date:	Mon, 29 Oct 2007 10:16:55 +0900
From:	Tsutomu Fujii <t-fujii@...jp.nec.com>
To:	netdev@...r.kernel.org
Subject: Bonding in active-backup mode with arp monitoring on Xen

Hi.

I was trying to use bonding from a guest OS on xen in active-backup
mode with arp monitoring, but the virtual server can't communicate to
the peer server via bonding interface.

The network structure is the following.

+-------------------------------+
|        virtual I/F(eth0)      | <- have IP address.
+-------------------------------+
|      virtual bridge(xenbr0)   |
+-------------------------------+
|         bonding(bond0)        | <- don't have IP address
+--------------+-+--------------+
|phy I/F(peth0)| |phy I/F(peth1)|
+--------------+ +--------------+

The attached file describes how I configured the network.

In this case, when I run 'cat /proc/net/bonding/bond0', 'MII Status'
is shown as down.

This behavior only occurs in active-backup mode with arp monitoring.
It does not happen in active-backup mode with mii monitoring nor other
mode that can use arp monitoring.

>From the output of tcpdump, it seems that arp packet isn't transmitted.
This problem is caused because bond_activebackup_arp_mon(), which is the
function that sends arp packet in active-backup mode, checks whether
bonding master interface has an IP address(bond_has_ip()), before arp
packets are transmitted using bond_arp_send_all().
In the above setting, bonding master interface don't have IP address.

How about removing bond_has_ip() from the condition for calling
bond_arp_send_all() to use bonding with xen?
When I removed bond_has_ip(), the resulting kernel worked fine and
active-backup mode works with arp monitoring.

I confirmed this behavior in RHEL5(2.6.18-44.el5xen). And I confirmed
that the upstream kernel(2.6.23) also has the same condition before
calling bond_arp_send_all().

Thanks.

---
Tsutomu Fujii

View attachment "set_bonding.txt" of type "text/plain" (1444 bytes)