wiki:TipAndDoc/network/defaultgw

Version 1 (modified by mitty, 15 years ago) (diff)

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  1. default gateway
  2. 複数設定されているとき
    1. CentOS
      1. ifcfg-eth?
        1. 結論

default gateway

  • default gateway (default route)の変更方法・扱い

複数設定されているとき

CentOS

ifcfg-eth?

  • ifcfg-eth? に書いた場合
  • /etc/sysconfig/network-scripts/ifcfg-eth0 
    DEVICE=eth0
BOOTPROTO=static
IPADDR=192.168.40.200
NETMASK=255.255.255.0
GATEWAY=192.168.40.1
ONBOOT=yes
  • /etc/sysconfig/network-scripts/ifcfg-eth1 
    DEVICE=eth1
BOOTPROTO=static
IPADDR=192.168.50.200
NETMASK=255.255.255.0
GATEWAY=192.168.50.1
ONBOOT=yes
  • service network restart 
    Bringing up interface eth0:                                [  OK  ]
Bringing up interface eth1:                                [  OK  ]
  • 結果 => route 
    Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.50.0    *               255.255.255.0   U     0      0        0 eth1
192.168.40.0    *               255.255.255.0   U     0      0        0 eth0
169.254.0.0     *               255.255.0.0     U     0      0        0 eth1
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth1
    • この状態で、実際にWANへpingを送るとeth1を通る
    • tcpdump icmp -n -i eth1 
      listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
01:32:42.314543 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 16947, seq 1, length 64
01:32:42.330849 IP 219.94.129.108 > 192.168.50.200: ICMP echo reply, id 16947, seq 1, length 64
  • eth0とeth1を逆にしてみる
    • eth0 
      IPADDR=192.168.50.200
NETMASK=255.255.255.0
GATEWAY=192.168.50.1
    • eth1 
      IPADDR=192.168.40.200
NETMASK=255.255.255.0
GATEWAY=192.168.40.1
    • service network restart 
      Bringing up interface eth0:                                [  OK  ]
Bringing up interface eth1:                                [  OK  ]
    • 結果 => route 
      Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.50.0    *               255.255.255.0   U     0      0        0 eth0
192.168.40.0    *               255.255.255.0   U     0      0        0 eth1
169.254.0.0     *               255.255.0.0     U     0      0        0 eth1
default         192.168.40.1    0.0.0.0         UG    0      0        0 eth1
      • 今度もeth1を通る
      • tcpdump icmp -n -i eth1 
        listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
01:39:05.380029 IP 192.168.40.200 > 219.94.129.108: ICMP echo request, id 26423, seq 1, length 64
01:39:05.392541 IP 219.94.129.108 > 192.168.40.200: ICMP echo reply, id 26423, seq 1, length 64
  • LinkUPの順番を変える
    • ifup eth1; ifup eth0 
      Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.50.0    *               255.255.255.0   U     0      0        0 eth0
192.168.40.0    *               255.255.255.0   U     0      0        0 eth1
169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0
    • tcpdump icmp -n -i eth0 
      listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
01:42:55.952191 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 52536, seq 1, length 64
01:42:55.965580 IP 219.94.129.108 > 192.168.50.200: ICMP echo reply, id 52536, seq 1, length 64

結論

  • 最後にLinkUPしたデバイスのgatewayが有効になる