wiki:TipAndDoc/network/defaultgw

Version 8 (modified by mitty, 15 years ago) (diff)

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  1. default gateway
  2. CentOS
    1. 複数NICでdhcp時
    2. ifcfg-eth?
    3. sysconfig/network
    4. 結論
      1. 例
    5. route コマンド
    6. default が複数あるときの挙動
      1. 例1
      2. 例2
      3. 例3
  3. Ubuntu
    1. 複数NICでdhcp時
    2. interfaces
    3. route コマンド

default gateway

  • default gateway (default route)の変更方法・扱い
  • ip route flush cacheでRPDBの更新をせずにパケットの経路を確かめていた箇所があるので、要検証・要修正

CentOS

複数NICでdhcp時

  • 最後にLinkUPしたNICのdefaultGWのみ有効になる
    • ifconfig 
      eth0      Link encap:Ethernet  HWaddr 00:0C:29:XX:XX:XX
          inet addr:133.XX.XX.177  Bcast:133.51.87.255  Mask:255.255.248.0
(snip)

eth1      Link encap:Ethernet  HWaddr 00:0C:29:YY:YY:YY
          inet addr:192.168.50.132  Bcast:192.168.50.255  Mask:255.255.255.0
(snip)

eth2      Link encap:Ethernet  HWaddr 00:0C:29:ZZ:ZZ:ZZ
          inet addr:192.168.40.156  Bcast:192.168.40.255  Mask:255.255.255.0
(snip)

eth3      Link encap:Ethernet  HWaddr 00:0C:29:XY:ZX:YZ
          inet addr:192.168.0.155  Bcast:192.168.0.255  Mask:255.255.255.0
(snip)
    • ip route 
      192.168.50.0/24 dev eth1  proto kernel  scope link  src 192.168.50.132
192.168.0.0/24 dev eth3  proto kernel  scope link  src 192.168.0.155
192.168.40.0/24 dev eth2  proto kernel  scope link  src 192.168.40.156
133.51.80.0/21 dev eth0  proto kernel  scope link  src 133.51.80.177
169.254.0.0/16 dev eth3  scope link
default via 192.168.0.1 dev eth3

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

sysconfig/network

  • /etc/sysconfig/network 
    GATEWAY=192.168.50.2
  • ifcfg-eth? に GATEWAY= があるとき
    • そちらが優先される
  • 無いとき
    • /etc/sysconfig/network の GATEWAY= が設定される 
      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         192.168.50.2    0.0.0.0         UG    0      0        0 eth0

結論

  • /etc/sysconfig/network-scripts/ifcfg-eth? に GATEWAY= の指定がない場合は、/etc/sysconfig/network が参照される
  • ifcfg-eth? に GATEWAY= の指定がある際は、そちらが参照される
    • NICが複数ある場合は、最後にLinkUPしたデバイスのgatewayが有効になる

例

  • eth0 
    GATEWAY=192.168.50.1
  • eth1
    • 指定なし
  • network 
    GATEWAY=192.168.50.2
  • => route 
    default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0

route コマンド

  • 以下の状態でroute addする 
    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         192.168.50.1    0.0.0.0         UG    0      0        0 eth0
  • route add default gw 192.168.40.1 
    default         192.168.40.1    0.0.0.0         UG    0      0        0 eth1
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0
    • この場合、実際にはeth1を通る 
      listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
02:03:27.195895 IP 192.168.40.200 > 219.94.129.108: ICMP echo request, id 51265, seq 1, length 64
02:03:27.212349 IP 219.94.129.108 > 192.168.40.200: ICMP echo reply, id 51265, seq 1, length 64
  • route add default gw 192.168.0.1 
    SIOCADDRT: Network is unreachable
    • routing table は変化せず

default が複数あるときの挙動

  • 挙動法則が不明
    • route コマンドで、先に表示された行のgwが必ず使われるとも限らない模様

  • ifconfig 
    eth0 => 192.168.50.100
eth1 => 192.168.60.100
eth2 => 192.168.70.100
eth3 => 192.168.40.100

例1

  • route 
    default         192.168.70.200  0.0.0.0         UG    0      0        0 eth2
default         192.168.60.200  0.0.0.0         UG    0      0        0 eth1
default         192.168.50.200  0.0.0.0         UG    0      0        0 eth0
default         192.168.40.200  0.0.0.0         UG    0      0        0 eth3
  • ping 219.94.129.108 -c1
    • client:eth2 (192.168.70.100) 
      03:20:58.808400 IP 192.168.70.100 > 219.94.129.108: ICMP echo request, id 33555, seq 1, length 64
    • gw:eth2 (192.168.70.200) 
      03:20:58.834723 IP 192.168.70.100 > 219.94.129.108: ICMP echo request, id 33555, seq 1, length 64

例2

  • route 
    default         192.168.40.200  0.0.0.0         UG    0      0        0 eth3
default         192.168.50.200  0.0.0.0         UG    0      0        0 eth0
default         192.168.60.200  0.0.0.0         UG    0      0        0 eth1
default         192.168.70.200  0.0.0.0         UG    0      0        0 eth2
  • ping 219.94.129.108 -c1
    • client:eth1 (192.168.60.100) 
      03:25:08.077550 IP 192.168.60.100 > 219.94.129.108: ICMP echo request, id 37651, seq 1, length 64
    • gw:eth1 (192.168.60.200) 
      03:25:08.106974 IP 192.168.60.100 > 219.94.129.108: ICMP echo request, id 37651, seq 1, length 64

例3

  • route 
    default         192.168.50.200  0.0.0.0         UG    0      0        0 eth0
default         192.168.60.200  0.0.0.0         UG    0      0        0 eth1
default         192.168.70.200  0.0.0.0         UG    0      0        0 eth2
default         192.168.40.200  0.0.0.0         UG    0      0        0 eth3
  • ping 219.94.129.108 -c1
    • client:eth3 (192.168.40.100) 
      03:29:45.739584 IP 192.168.40.100 > 219.94.129.108: ICMP echo request, id 42515, seq 1, length 64
    • gw:eth3 (192.168.40.200) 
      03:29:45.773401 IP 192.168.40.100 > 219.94.129.108: ICMP echo request, id 42515, seq 1, length 64

Ubuntu

  • CentOSとは違い、NICの設定ファイルは一つにまとまっている
  • default が複数あるときの挙動については、CentOS同様に不明
    • 最後に活性化されたNICがdefault gwになる？ (そうとも限らない可能性があるので要検証)

複数NICでdhcp時

  • 最後にDHCPから取得できるdefaultGW全てが列挙される
    • ifconfig 
      eth0      Link encap:Ethernet  HWaddr 00:0c:29:xx:xx:xx
          inet addr:133.xx.xx.18  Bcast:133.51.87.255  Mask:255.255.248.0
(snip)

eth1      Link encap:Ethernet  HWaddr 00:0c:29:yy:yy:yy
          inet addr:192.168.50.128  Bcast:192.168.50.255  Mask:255.255.255.0
(snip)

eth2      Link encap:Ethernet  HWaddr 00:0c:29:zz:zz:zz
          inet addr:192.168.40.157  Bcast:192.168.40.255  Mask:255.255.255.0
(snip)

eth3      Link encap:Ethernet  HWaddr 00:0c:29:xy:zx:yz
          inet addr:192.168.0.222  Bcast:192.168.0.255  Mask:255.255.255.0
(snip)
    • ip route 
      192.168.50.0/24 dev eth1  proto kernel  scope link  src 192.168.50.128
192.168.0.0/24 dev eth3  proto kernel  scope link  src 192.168.0.222
192.168.40.0/24 dev eth2  proto kernel  scope link  src 192.168.40.157
133.51.80.0/21 dev eth0  proto kernel  scope link  src 133.51.81.18
default via 133.51.87.254 dev eth0
default via 192.168.0.1 dev eth3
default via 192.168.40.2 dev eth2
      • eth3にはGWが無いため設定されていない

interfaces

  • /etc/network/interfaces 
    auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 192.168.50.200
        netmask  255.255.255.0
        gateway 192.168.50.1

auto eth1
iface eth1 inet static
        address 192.168.60.200
        netmask 255.255.255.0
        gateway 192.168.60.100

auto eth2
iface eth2 inet static
        address 192.168.70.200
        netmask 255.255.255.0
        gateway 192.168.70.100

auto eth3
iface eth3 inet static
        address 192.168.40.200
        netmask 255.255.255.0
        gateway 192.168.40.1
  • route 
    Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.70.0    *               255.255.255.0   U     0      0        0 eth2
192.168.50.0    *               255.255.255.0   U     0      0        0 eth0
192.168.60.0    *               255.255.255.0   U     0      0        0 eth1
192.168.40.0    *               255.255.255.0   U     0      0        0 eth3
default         192.168.40.1    0.0.0.0         UG    100    0        0 eth3
default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
default         192.168.60.100  0.0.0.0         UG    100    0        0 eth1
default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
  • ping 219.94.129.108 -c1 
    listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
07:56:54.264373 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 12822, seq 1, length 64
07:56:54.284695 IP 219.94.129.108 > 192.168.50.200: ICMP echo reply, id 12822, seq 1, length 64
  1. sudo ifdown eth2; sudo ifup eth2
    • route 
      default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
default         192.168.40.1    0.0.0.0         UG    100    0        0 eth3
default         192.168.60.100  0.0.0.0         UG    100    0        0 eth1
default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
  2. sudo ifdown eth1; sudo ifup eth1
    • route 
      default         192.168.60.100  0.0.0.0         UG    100    0        0 eth1
default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
default         192.168.40.1    0.0.0.0         UG    100    0        0 eth3
default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
    • ping 219.94.129.108 -c1 
      08:01:24.453913 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 42262, seq 1, length 64
08:01:24.475447 IP 219.94.129.108 > 192.168.50.200: ICMP echo reply, id 42262, seq 1, length 64
  3. sudo ifdown eth0; sudo ifup eth0
    • route 
      default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
default         192.168.60.100  0.0.0.0         UG    100    0        0 eth1
default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
default         192.168.40.1    0.0.0.0         UG    100    0        0 eth3
    • ping 219.94.129.108 -c1 
      08:02:22.346792 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 56854, seq 1, length 64
08:02:22.368070 IP 219.94.129.108 > 192.168.50.200: ICMP echo reply, id 56854, seq 1, length 64

route コマンド

  • ifup コマンドとは別に保存される
    1. sudo route add default gw 192.168.40.1
    2. sudo route add default gw 192.168.50.1
    3. sudo route add default gw 192.168.60.100
    4. sudo ifdown eth2; sudo ifup eth2
    5. sudo ifdown eth0; sudo ifup eth0
    • route 
      Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.70.0    *               255.255.255.0   U     0      0        0 eth2
192.168.50.0    *               255.255.255.0   U     0      0        0 eth0
192.168.60.0    *               255.255.255.0   U     0      0        0 eth1
192.168.40.0    *               255.255.255.0   U     0      0        0 eth3
default         192.168.60.100  0.0.0.0         UG    0      0        0 eth1
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0
default         192.168.40.1    0.0.0.0         UG    0      0        0 eth3
default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
    • ping 219.94.129.108 -c1 
      08:35:41.384666 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 39704, seq 1, length 64
  • 更にifdown/ifupするとdefault routeも追加される
    1. sudo ifdown eth1; sudo ifup eth1 
      default         192.168.60.100  0.0.0.0         UG    0      0        0 eth1
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0
default         192.168.40.1    0.0.0.0         UG    0      0        0 eth3
default         192.168.60.100  0.0.0.0         UG    100    0        0 eth1
default         192.168.50.1    0.0.0.0         UG    100    0        0 eth0
default         192.168.70.100  0.0.0.0         UG    100    0        0 eth2
    • しかし、実際にパケットが通るのはeth0のまま
    • ping 219.94.129.108 -c1 
      08:37:52.757894 IP 192.168.50.200 > 219.94.129.108: ICMP echo request, id 52248, seq 1, length 64