@crystone #64 有啥不会用的，所有软件源里有的就装源里面的，别自己乱编译就行了。实在要用的绕不开的 Docker 里面用 Fedora coreos 作为容器就好

GRE Keepalive does not work
SOLUTION 已验证 - 已更新 2013 年七月 17 日 18:56 - English
环境
Red Hat Enterprise Linux
GRE Tunnel to remote device, such as Cisco router
GRE Keepalives configured on remote device
问题
Configuring GRE Keepalives between a network device (such as a Cisco router) and RHEL system result in the keepalives being dropped by the Linux machine, and the networking device considering the tunnel down.
决议
Linux does not support GRE Keepalives.

You may disable GRE Keepalives on the remote device, or use a workaround such as an IP SLA ping down the GRE tunnel.

根源
A GRE Keepalive is a "host to router" GRE packet encapsulated inside a "router to host" GRE packet. The idea being the host (in this case Linux) receives the packet, sees the packet is actually a GRE packet for the router, and sends it back out. The router receives this packet and knows the remote end is still responding.

The Linux FIB code is such that if it receives traffic where the source is a local unicast address, the traffic is considered invalid.

Observe the following code:

Raw
net/ipv4/fib_frontend.c

if (res.type != RTN_UNICAST) {
if (res.type != RTN_LOCAL || !accept_local)
goto e_inval_res;
}
A GRE tunnel is not "stateful", there is no handshake or negotiation, just one side sending encapsulated packets and one side accepting encapsulated packets. As long as the network between the two sides stays up, the tunnel is up. Lack of Keepalives doesn't mean the tunnel is "down", just that you have no knowledge of the network state of the remote system. You could monitor this on the router with IP SLA, or monitor the remote end separately outside the tunnel.

诊断步骤
Cisco GRE Keepalive documentation:
http://www.cisco.com/en/US/tech/tk827/tk369/technologies_tech_note09186a008048cffc.shtml#t5

Linux GRE documentation:
http://lartc.org/lartc.html#LARTC.TUNNEL.GRE

RHEL 8 从发布用到现在，感觉很舒服

@RYAN0UP #22 可是流行的发行版自带 JRE

SELinux 日常开着的表示。。。上次我自己找了个放进去都跑不起来

@BinRelay #8 你把所有规则都删掉然后 deny 所有出入站再看看？

只是默认规则没有针对环回地址而已啊，你不能保证用户不自定义防火墙规则

DataGrid 买 JB 全家桶送的，还挺好用的

告辞诉还不如直接用 vmware

我 24 岁，到手 1.6 万月供去掉公积金 1.1 万。。。

嘛，我同事孩子小学一年级就学 Python 了

@reus 为了内存占用消耗这么多 cpu 我觉得划不来😹😹😹

这两个例子。。。Java 的内存使用是 Go 翻倍但是运行时间却是 Go 的三分之一，综合算下来资源使用并不比 Go 高

@abcbuzhiming #14
regex-redux
source secs mem gz busy cpu load
Go
29.20 399,668 802 61.29 71% 55% 37% 47%
Java
10.48 645,680 740 31.62 72% 87% 74% 68%
binary-trees
source secs mem gz busy cpu load
Go
25.25 374,780 1013 87.65 87% 88% 86% 86%
Java
8.28 907,060 835 27.59 86% 90% 80% 77%

额。。。哪你咋不说 Go 的运行时间是 Java 的几倍呢。。。

@abcbuzhiming #12 看起来内存占用差不多啊 Java 虚拟机初始化了差不多 30-40MB，你看 Go CPU 占用都比 Java 高。感觉是默认的 GC 频率比较高吧

@blackbookbj #7 学啥语言能干的都一样，但是如果起步就写 Python 这样的高级语言的话，以后想学 C 和 Java 之类的低级中级语言会很痛苦。

你确定 Go 写得内个东西功能和 Java 的一样？

我初中学的 C 和 Java 所以我不知道中学生学 Python 有啥用。
嘛，数据分析的话，中学生先学好 Office 吧，就中学那点数据量 Excel 足够了，图表做出来还好看。