使用JNDI获取DNS SRV记录 [英] Get DNS SRV record using JNDI

问题描述

我正在尝试使用JNDI从DNS服务器获取SRV记录.

I am trying to get SRV records from a DNS server using JNDI.

Hashtable<String, String> env = new Hashtable<String, String>();
env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
env.put("java.naming.provider.url", "dns://dns.server.com");
DirContext ctx = new InitialDirContext(env);
Attributes attributes = ctx.getAttributes("_sip._udp", new String [] { "SRV" });
return attributes;

但是当尝试获取属性时，出现以下异常

But when trying to get attributes I get the following exception

DNS错误[根异常为 java.net.PortUnreachableException: ICMP端口不可达]；剩余的名字 '_sip._udp'

DNS error [Root exception is java.net.PortUnreachableException: ICMP Port Unreachable]; remaining name '_sip._udp'

我已验证主机-t srv _sip._udp.server.com返回有效的SRV记录.

I have verified host -t srv _sip._udp.server.com returns valid SRV record.

为什么会发生这种情况?

Any reason as why this might happen?

推荐答案

以下之一:dns.server.com不是有效的DNS服务器，没有_sip._udp的SRV记录，DNS服务未在端口上响应53(标准DNS端口)或您的Java代码错误.

One of the following: dns.server.com not a valid DNS server, does not have a SRV record for _sip._udp, the DNS service does not respond on port 53 (standard DNS port) or your Java code is wrong.

要诊断DNS服务器故障，可以尝试host -t SRV _sip._udp.server.com dns.server.com或dig @dns.server.com -t SRV _sip._udp.server.com确认服务器正常工作.

To diagnose DNS server troubles, you could try host -t SRV _sip._udp.server.com dns.server.com or dig @dns.server.com -t SRV _sip._udp.server.com to confirm that the server works.

如果host或dig返回期望的条目，请尝试对代码进行以下更改:

If host or dig return the expected entry, try the following changes to your code:

更改:

env.put("java.naming.provider.url", "dns://dns.server.com");

收件人:

env.put("java.naming.provider.url", "dns:");

(即，仅使用您操作系统的标准DNS解析度)

(i.e., just use your OS's standard DNS resolution)

更改:

ctx.getAttributes("_sip._udp", new String [] { "SRV" });

收件人:

ctx.getAttributes("_sip._udp.domain.com", new String [] { "SRV" });

因为SRV记录需要一个域名才能搜索，所以您最终会得到:

as SRV record require a domain name to search, so you'd end up with:

Hashtable<String, String> env = new Hashtable<String, String>();
env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
DirContext ctx = new InitialDirContext(env);
Attributes attributes = ctx.getAttributes("_sip._udp.domain.com", new String [] { "SRV" });
return attributes;

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