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本文作者：賽靈思工程師 Davis Zhang

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這個問題是Linux Kernel TCP/IP Stack對于同一子網的IP處理方式決定的，嚴格來說是個Linux普遍問題，不在于AMD-Xilinx Device、IP或者Driver。

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當eth0和eth1的IP 地址在一個subnet，TCP/IP stack會選取一個MAC作為主，eth0和eth1收到的ping包都會通過這個主MAC發送返回包，通常來說ifconfig先使能哪個MAC，它就是主MAC。比如eth0為主MAC，這個時候可以通過eth0的網線來ping eth1的IP，返回包也是直接通過eth0發送，就是說對eth1 IP的ping包不會在eth1收到，也不通過它發送，stack直接作出回應，并通過eth0發送。如果這個時候通過eth1的網線發送對eth1 IP的ping包，eth1可以收到，但是stack還是會通過eth0發送返回包，現象就是ping不通。

如果eth0和eth1的IP不在同一subnet，比如192.168.1.10/192.168.2.10，就沒有這些問題。通常不建議在linux里對多個MAC使用同一subnet，甚至有些vendor禁止這樣做。

https://access.redhat.com/solutions/30564
https://www.ibm.com/support/pages/node/6466713

如果確實需要使用同一subnet，可以參考下面的方法來重新設置路由。

//the below steps redirects packets meant to be output from eth0 to properly exit from eth1.?

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//enable support for multiple routing tables in kernel config.?

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Kernel Configuration?

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?→ Networking support → Networking options?

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[*] IP: advanced router?

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[*] IP: policy routing?

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CONFIG_IP_ADVANCED_ROUTER?

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CONFIG_IP_MULTIPLE_TABLES?

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?//type below command in linux console?

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echo -ne 0 > /proc/sys/net/ipv4/conf/all/rp_filter?

echo -ne 0 > /proc/sys/net/ipv4/conf/eth0/rp_filterecho -ne 0 > /proc/sys/net/ipv4/conf/eth1/rp_filter

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//For proper functionality i.e. ARP replies from eth1 to get generated when both eth0 and eth1 are in same subnet

echo -ne 0 > /proc/sys/net/ipv4/conf/all/arp_filterecho -ne 2 > /proc/sys/net/ipv4/conf/all/arp_ignoreecho -ne 0 > /proc/sys/net/ipv4/conf/eth0/arp_filterecho -ne 2 > /proc/sys/net/ipv4/conf/eth0/arp_ignoreecho -ne 0 > /proc/sys/net/ipv4/conf/eth1/arp_filterecho -ne 2 > /proc/sys/net/ipv4/conf/eth1/arp_ignore

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//Create a table called "new_rt_table" and create a routing rule that says any packet with a mark equal to '1' gets routed according to the "new_rt_table"(can name it whatever you want) table. The file /etc/iproute2/rt_tables is the only source of table names on the system. Internally, routing tables have integer identifiers.

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echo 1 new_rt_table >> /etc/iproute2/rt_tables?

ip rule add from all fwmark 1 table new_rt_table?

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//setup the "new_rt_table" table to route the packets via eth1?

ip route add default dev eth1 table new_rt_table?

ip route show table new_rt_table?

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//mark packets so that 'ip route' can route it through eth1?

iptables -F -t mangle?

iptables -t mangle -I OUTPUT -s-o eth0 -j MARK --set-mark 1

　　審核編輯：湯梓紅