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. arp_announce 用来限制，是否使用发送的端口的ip地址来设置ARP的源地址：
Real-server的ip地址：202.106.1.100(public local address)， 172.16.1.100(private local address)， 202.106.1.254(VIP) 如果发送到client的ip包产生的arp请求的源地址是202.106.1.254(VIP),那么LVS上的VIP就会被冲掉，因为交换机上现在的arp对应关系是Real-server上的VIP对应自己的一个MAC，那么LVS上的VIP就失效了。
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} “0″,代表对于arp请求，任何配置在本地的目的ip地址都会回应，不管该arp请求的目的地址是不是接口的ip；如果有多个网卡，并且网卡的ip都是一个子网，那么从一个端口进来的arp请求，别的端口也会发送回应。 “1″,代表如果arp请求的目的地址，不是该arp请求包进入的接口的ip地址，那么不回应。 “2″,要求的更苛刻，除了”1″的条件外，还必须要求arp发送者的ip地址和arp请求进入的接口的ip地址是一个网段的。
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