LVS负载均衡中arp_ignore和arp_annonuce参数配置的含义

echo "1" > /proc/sys/net/ipv4/conf/all/arp_ignore

echo "1" > /proc/sys/net/ipv4/conf/lo/arp_ignore

echo "2" > /proc/sys/net/ipv4/conf/lo/arp_announce

echo "2" > /proc/sys/net/ipv4/conf/all/arp_announce

arp_ignore - INTEGER
	Define different modes for sending replies in response to
	received ARP requests that resolve local target IP addresses:
	0 - (default): reply for any local target IP address, configured
	on any interface
	1 - reply only if the target IP address is local address
	configured on the incoming interface
	2 - reply only if the target IP address is local address
	configured on the incoming interface and both with the
	sender's IP address are part from same subnet on this interface
	3 - do not reply for local addresses configured with scope host,
	only resolutions for global and link addresses are replied
	4-7 - reserved
	8 - do not reply for all local addresses

	The max value from conf/{all,interface}/arp_ignore is used
	when ARP request is received on the {interface}

arp_announce - INTEGER
	Define different restriction levels for announcing the local
	source IP address from IP packets in ARP requests sent on
	interface:
	0 - (default) Use any local address, configured on any interface
	1 - Try to avoid local addresses that are not in the target's
	subnet for this interface. This mode is useful when target
	hosts reachable via this interface require the source IP
	address in ARP requests to be part of their logical network
	configured on the receiving interface. When we generate the
	request we will check all our subnets that include the
	target IP and will preserve the source address if it is from
	such subnet. If there is no such subnet we select source
	address according to the rules for level 2.
	2 - Always use the best local address for this target.
	In this mode we ignore the source address in the IP packet
	and try to select local address that we prefer for talks with
	the target host. Such local address is selected by looking
	for primary IP addresses on all our subnets on the outgoing
	interface that include the target IP address. If no suitable
	local address is found we select the first local address
	we have on the outgoing interface or on all other interfaces,
	with the hope we will receive reply for our request and
	even sometimes no matter the source IP address we announce.

	The max value from conf/{all,interface}/arp_announce is used.

	Increasing the restriction level gives more chance for
	receiving answer from the resolved target while decreasing
	the level announces more valid sender's information.

Assume that a linux box X has three interfaces - eth0, eth1 and eth2. Each interface has an IP address IP0, 

IP1 and IP2. When a local application tries to send an IP packet with IP0 through the eth2.  Unfortunately, 

the target node’s mac address is not resolved. Thelinux box X will send the ARP request to know 

the mac address of the target(or the gateway). In this case what is the IP source address of the 

“ARP request message”? The IP0- the IP source address of the transmitting IP or IP2 - the outgoing

 interface?  Until now(actually just 3 hours before) ARP request uses the IP address assigned to 

the outgoing interface(IP2 in the above example) However the linux’s behavior is a little bit 

different. Actually the selection of source address in ARP request is totally configurable 

bythe proc variable “arp_announce”  

If we want to use the IP2 not the IP0 in the ARP request, we should change the value to 1 or 2. 

The default value is 0 - allow IP0 is used for ARP request.