Linux主机双网卡同网段同网关配置

# 1. 网络架构
在同一台机配置双网卡，并且都使用同一子网网段的内网地址的网络架构图

```
+---------------------+
|       Linux         |
|   .168      .169    | 
+-----+--------+------+
      │        │
+-----+--------+------+
|       Switch        |
+---------+-----------+
          │
+---------+-----------+
|         .1          |
|       Gateway       |
+---------------------+
```

# 2. 常见问题
在同一台机配置双网卡，并且都使用同一子网网段的内网地址，则通常会出现**仅有一个网卡可实现正常访问**的现象
抓包发现应该从网卡1传送过来的数据包，实际上是由网卡2传送过来的数据包

推荐的解决方案是使用单个接口或单个绑定/组接口，然后以别名 IP 地址的形式将其他 IP 地址添加到该接口。如果在网络接口级别需要容错和/或负载平衡，则应使用绑定或团队的别名。请注意，Red Hat Enterprise Linux 6 或更早版本不支持分组。如果接口级别不需要容错和/或负载平衡，则可以将别名 IP 地址添加到单个接口。

# 3. 根本原因
当同一子网上有 2 个接口时，无法保证哪个接口将用于传输流量，机器将接受任一接口上任一IP的流量。
这是因为在 Linux 中，IP 地址属于主机，与接口无关。
如果您尝试使用`ping`命令并使用参数`-I DEV`指定接口，则无法保证回复数据包（如果有的话）会返回同一接口，因此`ping -I DEV`操作可能无法正常工作。

# 4. 解决办法
该脚本自动实现静态路由的更改和创建，您只需要提供您想要修改的子网。
```bash
#!/bin/sh

#    fixFlux.sh - Assigns fixed routes for each NIC
#                 residing on the same subnet to resolve
#                 the ARP FlUX problem
# See https://access.redhat.com/kb/docs/DOC-59096
#
#    Date: 7/21/2011
#    Update Date: 12/09/2022

SCRIPT_REVISION=1.1.0
SCRIPT_LOG=/dev/null

#    Author:  Ken Banks
#    Company: Kontron America.
#
# CHANGE LOG:
# 7/21/2011    1.0.1  Original code.
# 8/23/2011    1.0.2  Fix a bug with 'undo' to re-enble NetworkManager
#                     and another bug that allowed multiple 'no's to be
#                     added to NM_CONTROLLED= if the script was run more than once.
# 12/09/2022   1.1.0  Fix network card acquisition and ip acquisition error problems.

SYSCTL=/etc/sysctl.conf
RT_TABLES=/etc/iproute2/rt_tables

function usage() {
    echo "usage:  $0 subnet <undo>"
    echo "        version $SCRIPT_REVISION"
    echo "        : This script will solve the Arp Flux for multiple NICs"
    echo "        : residing on the same subnet, as described in this document:"
    echo "        : https://access.redhat.com/kb/docs/DOC-59096"
    echo
    echo " e.g.   $0 192.168.1      -  Configures a static route for ever IC on 192.168.1.0"
    echo "        $0 192.168.1 undo -  Reverts the changes caused above and re-instates NetworkManager"
}

function log_message() {

echo -e "$*"
    echo -e "$*"  >>  $SCRIPT_LOG

}

function  compareValues() {

awk "BEGIN { if ( $1 $2 $3 ) print \"TRUE\" }"

}

function addRoute() {

NICNAME=$1
    TABLENUM=$2
    TABLENAME=$3
    SUBNET=$4
    DEFAULTGW=$5
    NICIP=$6

FirstOctect=`echo $SUBNET | awk -F. '{ print $1 }'`

ip route show  | grep $6 > /dev/null

if [ "$?" != "0" ] ; then

echo ip route add  $SUBNET dev $NICNAME  src $NICIP table $TABLENAME
        ip route add  $SUBNET dev $NICNAME  src $NICIP table $TABLENAME
        echo ip route add table $TABLENAME default via $DEFAULTGW dev $NICNAME
        ip route add table $TABLENAME default via $DEFAULTGW dev $NICNAME
        #echo ip route show table $TABLENAME
        #ip route show table $TABLENAME

fi

ETHROUTE=/etc/sysconfig/network-scripts/route-$NICNAME
    echo $FirstOctect.0.0.0/8 dev $NICNAME src $NICIP table  $TABLENAME > $ETHROUTE
    echo default via $DEFAULTGW dev $NICNAME table  $TABLENAME >> $ETHROUTE
    echo "Modified: $ETHROUTE"

ETHRULE=/etc/sysconfig/network-scripts/rule-$NICNAME
    echo table $TABLENAME from $NICIP > $ETHRULE
    echo "Modified: $ETHRULE"

}

function disableNetworkManager() {

service NetworkManager status | grep stopped >/dev/null
    if [ "$?" != "0" ] ; then

service NetworkManager stop   > /dev/null

fi
    echo "NetworkManager service is stopped."
    chkconfig NetworkManager --list | grep :on >/dev/null

if [ "$?" == "0" ] ; then

chkconfig NetworkManager off  > /dev/null

fi

echo "NetworkManager service is disabled."
    ETHSCRIPT=/etc/sysconfig/network-scripts/ifcfg-$1
    TMPSCRIPT=/tmp/tmpcfg-$1
    grep -i NM_CONTROLLED=[\"yes\"]  $ETHSCRIPT | awk -F. '{ print $1 }'  > /dev/null

if [ "$?" == "0" ] ; then

cp $ETHSCRIPT  $TMPSCRIPT
        cat $TMPSCRIPT | sed  's/NM_CONTROLLED=["yes"].*/NM_CONTROLLED=no/' > $ETHSCRIPT
        echo "Modified: $ETHSCRIPT"

fi

}

function processNIC() {

#     inet 192.168.6.99/24 brd 192.168.6.255 scope global eth0show table

#     inet 192.168.6.60/24 brd 192.168.6.255 scope global eth1

export NICNAME=$1
    export TABLENUM=$2
    export TABLENAME=$3
    export SUBNET=$4
    export DEFAULTGW=`ip route | grep default | awk '{ print $3 }'`
    export NICDATA=`ifconfig -a $NICNAME | grep broadcast`
    NICIP=`echo $NICDATA | awk '{ print $2 }'`

if [ "$NICIP" == "" ] ; then

echo "ERROR: No IP for this NIC: $NICNAME"
        exit

fi

echo "====PROCESS NIC==== $NICDATA"
    echo "====  $NICNAME ===="
    grep $TABLENAME $RT_TABLES > /dev/null

if [ "$?" != "0" ] ; then

echo "Creating route table: $TABLENUM  $TABLENAME"
        echo "$TABLENUM  $TABLENAME"  >> $RT_TABLES

else

echo "Route table already exists: $TABLENUM  $TABLENAME"

fi

addRoute $NICNAME $TABLENUM $TABLENAME $SUBNET  $DEFAULTGW $NICIP
    disableNetworkManager $NICNAME
    echo

}

function delete_route() {

ip route delete $1 dev $2

}

function undo_routes() {

SUBNET=$1
      echo 0 > /proc/sys/net/ipv4/conf/default/arp_filter
      echo 0 > /proc/sys/net/ipv4/conf/all/arp_filter
      cp $RT_TABLES /tmp/rt_tables
      grep -v "^.00  t[0-9]*" /tmp/rt_tables > $RT_TABLES
      rm -f /etc/sysconfig/network-scripts/r[ou][ul][te]*

for i in `ip route show | grep src | awk '{ print $1"-"$3 }'` ; do
            delete_route  `echo $i | sed 's/-/ /'`
      done
      grep net.ipv4.conf.all.arp_filter $SYSCTL  > /dev/null

if [ "$?" == "0" ] ; then

grep  "arp_filter[ =]*0" $SYSCTL  > /dev/null

if [ "$?" != "0" ] ; then

cp $SYSCTL  /tmp/tmpctl.conf
            cat /tmp/tmpctl.conf | sed 's/arp_filter[ =]*./arp_filter = 0/' >> $SYSCTL
            echo "Modified: $SYSCTL"

fi

for device in `ip addr | grep $SUBNET | awk '{ print $8 }'` ; do

ETHSCRIPT=/etc/sysconfig/network-scripts/ifcfg-$devic
        TMPSCRIPT=/tmp/tmpcfg-$device
        grep -i NM_CONTROLLED=[\"no\"]  $ETHSCRIPT | awk -F. '{ print $1 }'  > /dev/null

if [ "$?" == "0" ] ; then

cp $ETHSCRIPT  $TMPSCRIPT
            cat $TMPSCRIPT | sed  's/NM_CONTROLLED=[\"no\"].*/NM_CONTROLLED=yes/' > $ETHSCRIPT
            echo "Modified: $ETHSCRIPT"

fi

done

chkconfig NetworkManager on

service NetworkManager start

}

function main() {

[ "$1" == "" ] && usage && exit
    SUBNET=$1
    [ "$2" == "undo" ] && undo_routes $SUBNET  && exit

echo "# $0 $*"
    log_message  "=========================================================================="
    log_message  "=============================BEGIN ROUTE CREATION========================="
    log_message  "=========================================================================="

table=1

for device in `ip addr | grep $SUBNET | awk '{ print $7 }'` ; do

processNIC $device $((100 * $table))  t$table  $SUBNET
        table=$((1 + $table))

done

echo 1 > /proc/sys/net/ipv4/conf/default/arp_filter

echo "set /proc/sys/net/ipv4/conf/default/arp_filter = 1"

echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter

echo "set /proc/sys/net/ipv4/conf/all/arp_filter = 1"

grep net.ipv4.conf.all.arp_filter $SYSCTL  > /dev/null

if [ "$?" != "0" ] ; then

echo "net.ipv4.conf.all.arp_filter = 1" >>  $SYSCTL
        echo "Modified: $SYSCTL"

else

grep  "arp_filter[ =]*1" $SYSCTL  > /dev/null

if [ "$?" != "0" ] ; then

cp $SYSCTL  /tmp/tmpctl.conf
            cat /tmp/tmpctl.conf | sed 's/arp_filter[ =]*./arp_filter = 1/' >> $SYSCTL
            echo "Modified: $SYSCTL"

fi

service network restart

log_message  "=========================================================================="
    log_message  "==========================ROUTES HAVE BEEN CREATED========================"
    log_message  "=========================================================================="

echo "Contents of file: $RT_TABLES"
    cat $RT_TABLES
    echo "Command output from: ip route show"
    ip route show

}

main $*
```

>原文地址:  [*如何连接同一子网上的两个网络接口* ](https://access.redhat.com/solutions/30564 "如何连接同一子网上的两个网络接口")
>(因源文中的脚本在使用中存在问题，已在上述脚本中修正)