Linux测试lo

偶然将UDP的接收端关闭,测试性能的时候,查看数据口和lo的bps情况,发现ifconfig里lo的bps比平常大了一倍左右,应该与其机制有关,干脆简单测试一把

1:直接ping本地

[lihui@master script]$ ping 127.0.0.1

2:脚本打印ifconfig的输出结果,ping 3次结束掉,此时RX的包数每次多两个包

[lihui@master script]$ ./nic_traffic.pl lo
####################################################################################
used memory:  3.523G            cached:  2.100G         swap:  0G
Nic lo     bps:    1.312   bits/s          packets:    5879   dropped:      0 pkts/s
####################################################################################
used memory:  3.523G            cached:  2.100G         swap:  0G
Nic lo     bps:    1.312   bits/s          packets:    5881   dropped:      0 pkts/s
####################################################################################
used memory:  3.523G            cached:  2.100G         swap:  0G
Nic lo     bps:    1.312   bits/s          packets:    5883   dropped:      0 pkts/s
####################################################################################

3:同时监听lo口,将所有包抓下来

[lihui@master script]$ sudo tcpdump -i lo -w ping.pcap

4:查看一下包信息

[lihui@master script]$ tshark -r ping.pcap
  1   0.000000    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) request  id=0x1870, seq=1/256, ttl=64
  2   0.000026    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) reply    id=0x1870, seq=1/256, ttl=64 (request in 1)
  3   0.999233    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) request  id=0x1870, seq=2/512, ttl=64
  4   0.999255    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) reply    id=0x1870, seq=2/512, ttl=64 (request in 3)
  5   1.999209    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) request  id=0x1870, seq=3/768, ttl=64
  6   1.999232    127.0.0.1 -> 127.0.0.1    ICMP 98 Echo (ping) reply    id=0x1870, seq=3/768, ttl=64 (request in 5)

可见,我一共ping了3次,从上面脚本来看,每次多捕获了两个数据包,从这里分析数据包的结果,每次ping都有一个request和一个reply

5:再看UDP的情况

UDP接收程序关闭的时候,监听端口进程关闭,包信息如下

6178   1.139939    127.0.0.1 -> 127.0.0.1    CFLOW 286 total: 1 (v9) record
6179   1.139943    127.0.0.1 -> 127.0.0.1    ICMP 314 Destination unreachable (Port unreachable)
6180   1.139957    127.0.0.1 -> 127.0.0.1    CFLOW 486 total: 1 (v9) record
6181   1.139961    127.0.0.1 -> 127.0.0.1    ICMP 514 Destination unreachable (Port unreachable)
6182   1.139986    127.0.0.1 -> 127.0.0.1    CFLOW 598 total: 1 (v9) record
6183   1.139991    127.0.0.1 -> 127.0.0.1    ICMP 590 Destination unreachable (Port unreachable)

从这里可以看到,由于监听端口的进程被我关闭了,因此虽然UDP发出去了,但是没有被接收,因此local就产生了一个相当于报错信息的ICMP包,这也就是为什么bps会增大一倍的原因

将监听端口程序打开,继续抓包分析,UDP全都成功发出和接收,少了一半的ICMP,所以lo的流量自然少了一半左右~!

4125   1.072155    127.0.0.1 -> 127.0.0.1    CFLOW 246 total: 1 (v9) record
4126   1.072169    127.0.0.1 -> 127.0.0.1    CFLOW 410 total: 1 (v9) record
4127   1.072184    127.0.0.1 -> 127.0.0.1    CFLOW 502 total: 1 (v9) record
4128   1.072200    127.0.0.1 -> 127.0.0.1    CFLOW 694 total: 1 (v9) record
4129   1.072216    127.0.0.1 -> 127.0.0.1    CFLOW 622 total: 1 (v9) record

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