====== CentOS 兩張網卡接兩個 ISP 的 Route 設定 ======
  * 一台主機的兩張網卡各連接一個 ISP 的網路
  * 希望透過哪張網卡過來的連線, 可以直接由那張網卡回去
  * 這台主機的相關環境如下:
    * eth0 : 192.168.11.248 / 255.255.255.0 (Gateway pdc.e2160 : 192.168.11.251)
    * eth1 : 192.168.12.246 / 255.255.255.0 (Gateway c2q.q9400 : 192.168.12.250)
    * 預設 default gateway 走 192.168.11.251 有異常時, 自動改走 192.168.12.250

===== 設定程序 =====
  * 編輯 rt_tables<code sh>
vi /etc/iproute2/rt_tables
</code><file>
:
#
# local
#
#1      inr.ruhep
1       c2q.q9400
2       pdc.e2160
</file>
  * 定義 route 規則<code sh>
ip route add 192.168.11.0/24 dev eth0 src 192.168.11.248 table pdc.e2160
ip route add default via 192.168.11.251 table pdc.e2160
ip rule add from 192.168.11.248 table pdc.e2160

ip route add 192.168.12.0/24 dev eth1 src 192.168.12.246 table c2q.q9400
ip route add default via 192.168.12.250 table c2q.q9400
ip rule add from 192.168.12.246 table c2q.q9400

ip route add default scope global nexthop via 192.168.11.251 dev eth0 weight 1 nexthop via 192.168.12.250 dev eth1 weight 4

</code>
  * 編輯 route-ethx rule-ethx<code sh>
vi /etc/sysconfig/network-scripts/route-eth0
</code><file>
192.168.11.0/24 dev eth0 src 192.168.11.248 table pdc.e2160
default via 192.168.11.251 table pdc.e2160
</file><code sh>
vi /etc/sysconfig/network-scripts/rule-eth0
</code><file>
from 192.168.11.248 table pdc.e2160
</file><code sh>
vi /etc/sysconfig/network-scripts/route-eth1
</code><file>
192.168.12.0/24 dev eth1 src 192.168.12.246 table c2q.q9400
default via 192.168.12.250 table c2q.q9400
default scope global nexthop via 192.168.11.251 dev eth0 weight 1 nexthop via 192.168.12.250 dev eth1 weight 4
</file><code sh>
vi /etc/sysconfig/network-scripts/rule-eth1
</code><file>
from 192.168.12.246 table c2q.q9400
</file>
  * 檢視設定結果<code sh>
[root@xen-server ~]# ip route show
192.168.12.0/24 dev eth1  proto kernel  scope link  src 192.168.12.246
192.168.11.0/24 dev eth0  proto kernel  scope link  src 192.168.11.248
169.254.0.0/16 dev eth1  scope link
default
        nexthop via 192.168.11.251  dev eth0 weight 1
        nexthop via 192.168.12.250  dev eth1 weight 4
</code>

===== 發生異常強制設定程序 =====
  * 假設 eth0 : 192.168.11.248 / 255.255.255.0 (Gateway pdc.e2160 : 192.168.11.251) 這個 ISP 確定短時間無法修復, 簡單的拿掉設定方式如下:
<code sh>
vi /etc/sysconfig/network-scripts/route-eth1
</code><file>
192.168.12.0/24 dev eth1 src 192.168.12.246 table c2q.q9400
default via 192.168.12.250 table c2q.q9400
#default scope global nexthop via 192.168.11.251 dev eth0 weight 1 nexthop via 192.168.12.250 dev eth1 weight 4
default scope global nexthop via 192.168.12.250 dev eth1 weight 4
</file><code sh>
service network restart 
</code>
  * 檢視設定結果<code sh>
[root@xen-server ~]# ip route show
192.168.12.0/24 dev eth1  proto kernel  scope link  src 192.168.12.246
192.168.11.0/24 dev eth0  proto kernel  scope link  src 192.168.11.248
169.254.0.0/16 dev eth1  scope link
default via 192.168.12.250 dev eth1
</code>


===== 參考資料 =====
  * http://lartc.org/howto/lartc.rpdb.multiple-links.html
  * http://tech.gaeatimes.com/index.php/archive/how-to-load-balancing-failover-with-dual-multi-wan-adsl-cable-connections-on-linux/

{{tag>network multi-isp}}