在IPv6源地址选择Linux中的流量：
中我在接口上有一些IPv6地址。我希望内核选择其中一个作为源IPv6 ADDR。我不希望内核选择这个我将要发送它作为即将发出的数据包的源地址。
更具体地说，在此片段中，我希望内核在此界面上选择任何其他IPv6地址时，当DontuseasSourCeadDressForoutOndoDONDONDONGE是正确的。哪些旗帜会产生这种效果？如果我使用错误的IFADDRMSG struct进行IPv6地址，我应该使用哪个？
摘要包含进一步的上下文：
int
NetLnkSock::IpAdd(const std::string &ifname,
const IpAddr &ipaddr,
int prefixlen,
bool dontUseAsSourceAddressForOutgoingPkts)
ifreq ifr;
nlmsghdr *nlh;
ifaddrmsg *ifa;
nlmsgerr *nlerr;
static uint32_t msg_seq = 0;
NlSock nlsock;
LogDev::Ostream logostr;
nlsock.bind();
memset(&ifr, 0, sizeof(ifr));
if (ifname.size() > IFNAMSIZ)
throw NetLnkNameErr();
copy(ifname.begin(), ifname.end(), ifr.ifr_name);
ifr.ifr_name[ifname.end() - ifname.begin()] = ' ';
nlh = (nlmsghdr *)rcvbuf;
nlh->nlmsg_len = sizeof(nlmsghdr);
nlh->nlmsg_type = RTM_NEWADDR;
nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
nlh->nlmsg_seq = ++msg_seq;
nlh->nlmsg_pid = 0;
ifa = (ifaddrmsg *)&nlh[1];
ifa->ifa_family = (ipaddr.is_v4()) ? AF_INET : AF_INET6;
ifa->ifa_prefixlen = prefixlen;
/*
* My question is about the behavior of the kernel
* vis a vis source address selection for outgoing traffic
* where there are multiple IP's on this interface.
* How do the flags below impact the kernel's choice
* for source address selection?
*/
ifa->ifa_flags =
(dontUseAsSourceAddressForOutgoingPkts && ipaddr.is_v6()) ?
(IFA_F_SECONDARY | IFA_F_DEPRECATED) : 0;
/*
* I would like for the kernel to select any other IPv6
* address already on this interface when
* dontUseAsSourceAddressForOutgoingPkts is true.
* Will these flags yield that effect?
*/
ifa->ifa_scope = RT_SCOPE_UNIVERSE;
ifa->ifa_index = ifr.ifr_ifindex;
nlh->nlmsg_len += sizeof(ifaddrmsg);
if (ipaddr.is_v4()) {
IpAddr ip4_bcast;
char *buf = rcvbuf + nlh->nlmsg_len;
ip4_bcast.create_netmask(prefixlen, ipaddr);
ip4_bcast.from_v4(~ip4_bcast.get_v4() | ipaddr.get_v4());
nlh->nlmsg_len += NLMSG_ALIGN(setRtAttr(buf, IFA_LOCAL,
&ipaddr.get_v4(), sizeof(in_addr_t)));
/*
* Always send the netmask and broadcast even on delete.
* Linux seems to ignore the prefixlen set in the original
* message and simply matches by ip address on deletes.
*/
buf = rcvbuf + nlh->nlmsg_len;
nlh->nlmsg_len += NLMSG_ALIGN(setRtAttr(buf, IFA_ADDRESS,
&ipaddr.get_v4(), sizeof(in_addr_t)));
buf = rcvbuf + nlh->nlmsg_len;
nlh->nlmsg_len += NLMSG_ALIGN(setRtAttr(buf, IFA_BROADCAST,
&ip4_bcast.get_v4(), sizeof(in_addr_t)));
} else { /* AF_INET6 */
char *buf = rcvbuf + nlh->nlmsg_len;
buf = rcvbuf + nlh->nlmsg_len;
if (ipaddr.domain() != RD_DEFAULT_ID) { // Hal doesn't support route domains
throw NetLnkIpAddrErr();
}
nlh->nlmsg_len += NLMSG_ALIGN(setRtAttr(buf, IFA_LOCAL,
&ipaddr.get_v6(), sizeof(in6_addr)));
buf = rcvbuf + nlh->nlmsg_len;
nlh->nlmsg_len += NLMSG_ALIGN(setRtAttr(buf, IFA_ADDRESS,
&ipaddr.get_v6(), sizeof(in6_addr)));
}
nlsock.sendNlReq(rcvbuf);
}
rfc 3484状态：
-
源地址选择
＆lt; ...＆gt;
规则3：避免弃用的地址。地址SA和SB具有相同的范围。如果两个源地址是"优先"其中之一是"弃用"(在RFC 2462 Sense(，然后更喜欢"首选"。
＆lt; ...＆gt;
rtnetlink(7(男人页面简要提及一个名为ifa_cacheinfo的结构。
此结构包含两个值得注意的标志：ifa_valid和ifa_prefered。为了将IPv6地址标记为已弃用，将其首选_lft设置为零。此外，似乎习惯性地将有效的_lft设置为0xffffffff(Forever(以强调此IPv6地址的明确弃用性质。
/*
* You have just put a new IPv6 address on the kernel with
* net link. You don't want it chosen as the source address
* of packets leaving this interface if there's at least one
* other IPv6 address already on this interface.
*
* Mark this IPv6 address as Deprecated on this interface,
* Causing LINUX not to choose it for source address of
* packets outgoing from this interface when there exists
* another, non-deprecated IPv6 address on this interface
*/
struct ifa_cacheinfo ci;
// This address is valid forever
ci.ifa_valid = 0xffffffff;
// A prefered ttl of 0 immediately deprecates this IPv6
ci.ifa_preferred = 0;
// <Send this cacheinfo to the kernel using net link>
rtnetlink(7)男人页面只说：
ifa_flags是辅助地址(旧别名接口(的IFA_F_SECONDARY的标志单词，用户设置的永久地址和其他无证标志的IFA_F_PERMANENT。
的确，内核资料似乎没有记录下来：
/* ifa_flags */
#define IFA_F_SECONDARY 0x01
#define IFA_F_TEMPORARY IFA_F_SECONDARY
#define IFA_F_NODAD 0x02
#define IFA_F_OPTIMISTIC 0x04
#define IFA_F_DADFAILED 0x08
#define IFA_F_HOMEADDRESS 0x10
#define IFA_F_DEPRECATED 0x20
#define IFA_F_TENTATIVE 0x40
#define IFA_F_PERMANENT 0x80
#define IFA_F_MANAGETEMPADDR 0x100
#define IFA_F_NOPREFIXROUTE 0x200
#define IFA_F_MCAUTOJOIN 0x400
#define IFA_F_STABLE_PRIVACY 0x800
但是，RFC 3549" Linux Netlink作为IP服务协议"澄清更多：
Flags: 8 bits
IFA_F_SECONDARY For secondary address (alias interface).
IFA_F_PERMANENT For a permanent address set by the user.
When this is not set, it means the address
was dynamically created (e.g., by stateless
autoconfiguration).
IFA_F_DEPRECATED Defines deprecated (IPV4) address.
IFA_F_TENTATIVE Defines tentative (IPV4) address (duplicate
address detection is still in progress).
因此，这两个标志似乎没有相关：一个标记将接口地址标记为次要(临时(；另一个定义了一个IPv4地址('dreaked'(。
如果您需要准确查看每个标志的含义，则可以查看源代码中符号的引用，例如在IFA_F_SECONDARY和IFA_F_DEPRECATED。