今天我得到了一個有 2 個 IP 位址的 VPS。
當我這樣做時， IPeth0正在工作，ping -I eth0 www.google.com我的資料包遺失率為 0%，但當我這樣做時，ping -I eth1 www.goole.com我的資料包遺失率為 100%。
這是ifconfig輸出：
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 185.8.49.12 netmask 255.255.255.0 broadcast 185.8.49.255
inet6 fe80::250:56ff:fe84:5ed6 prefixlen 64 scopeid 0x20<link>
ether 00:50:56:84:5e:d6 txqueuelen 1000 (Ethernet)
RX packets 5716 bytes 398892 (389.5 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 933 bytes 294738 (287.8 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
eth1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 185.8.49.157 netmask 255.255.255.0 broadcast 185.8.49.255
ether 00:50:56:84:5e:d7 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 0 (Local Loopback)
RX packets 56 bytes 8896 (8.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 56 bytes 8896 (8.6 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
這是以下的輸出ifcfg-eth0：
DEVICE=eth0
NM_CONTROLLED=no
ONBOOT=yes
TYPE=Ethernet
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
BOOTPROTO=none
IPADDR=185.8.49.12
NETMASK=255.255.255.0
GATEWAY=185.8.49.1
DNS1=62.149.128.4
DNS2=62.149.132.4
這是輸出ifcfg-eth1：
DEVICE=eth1
NM_CONTROLLED=no
ONBOOT=yes
TYPE=Ethernet
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth1"
BOOTPROTO=none
IPADDR=185.8.49.157
NETMASK=255.255.255.0
GATEWAY=185.8.49.1
我嘗試過重新啟動系統，但沒有任何效果。
答案1
兩個介面設定上的「DEFROUTE=yes」並沒有像您想像的那樣執行。
重新啟動（以清除您所做的所有修改）並執行“ip route”。
您應該會看到類似以下內容：
# ip route
default via 185.8.49.1 dev eth0
185.8.49.0/24 dev eth0 proto kernel scope link src 185.8.49.12
185.8.49.0/24 dev eth1 proto kernel scope link src 185.8.49.157
當您發出「ping -I eth1 8.8.8.8」時，由於系統未配置可從 eth1 存取的預設網關，因此 ARP 要求將傳送至所有介面以在本機網路上尋找 8.8.8.8：
# ping -I eth1 8.8.8.8
PING 8.8.8.8 (8.8.8.8) from 185.8.49.157 eth1: 56(84) bytes of data.
From 185.8.49.157 icmp_seq=1 Destination Host Unreachable
From 185.8.49.157 icmp_seq=2 Destination Host Unreachable
From 185.8.49.157 icmp_seq=3 Destination Host Unreachable
From 185.8.49.157 icmp_seq=4 Destination Host Unreachable
# tcpdump -ni eth0 'arp'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
05:07:42.821526 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 46
05:07:43.821185 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 46
05:07:44.823000 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 46
# tcpdump -ni eth1 'arp'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
05:07:42.820834 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 28
05:07:43.820864 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 28
05:07:44.822841 ARP, Request who-has 8.8.8.8 tell 185.8.49.157, length 28
（顯然 Google 的 DNS 伺服器與您的 VPS 不在同一子網路中。）
繼續嘗試新增第二條預設路由：
# ip route add default via 185.8.49.1 dev eth1
RTNETLINK answers: File exists
看起來系統不會輕易接受多個預設路由。
這是有道理的 - 設備如何知道透過其多個網關中的哪一個發送資料包？它會為每個網關發送一份副本...然後處理多個返回資料包嗎？或者它會以不確定的方式任意發送資料包（故障排除的噩夢）？
想必它可以負載平衡，所以讓我們試試看：
#ip route delete default
#ip route add default scope global nexthop via 185.8.49.1 dev eth0 weight 1 nexthop via 185.8.49.1 dev eth1 weight 1
#ip ro
default
nexthop via 185.8.49.1 dev eth0 weight 1
nexthop via 185.8.49.1 dev eth1 weight 1
...
但這有效嗎？
# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=54 time=17.6 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=54 time=18.7 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=54 time=17.1 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=54 time=15.3 ms
^C
--- 8.8.8.8 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 15.337/17.227/18.762/1.241 ms
# tcpdump -ni eth0 icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
05:46:31.837933 IP 185.8.49.12 > 8.8.8.8: ICMP echo request, id 2382, seq 1, length 64
05:46:31.855566 IP 8.8.8.8 > 185.8.49.12: ICMP echo reply, id 2382, seq 1, length 64
05:46:33.842373 IP 185.8.49.12 > 8.8.8.8: ICMP echo request, id 2382, seq 3, length 64
05:46:33.859469 IP 8.8.8.8 > 185.8.49.12: ICMP echo reply, id 2382, seq 3, length 64
# tcpdump -ni eth1 icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
05:46:32.840535 IP 185.8.49.157 > 8.8.8.8: ICMP echo request, id 2382, seq 2, length 64
05:46:32.859029 IP 8.8.8.8 > 185.8.49.157: ICMP echo reply, id 2382, seq 2, length 64
05:46:34.843725 IP 185.8.49.157 > 8.8.8.8: ICMP echo request, id 2382, seq 4, length 64
05:46:34.859020 IP 8.8.8.8 > 185.8.49.157: ICMP echo reply, id 2382, seq 4, length 64
達達！
現在由您決定是否需要負載平衡真的需要並願意支持。