I have an Power710 with AIX 6.1 with several network cards. I configured all of them and two have IPs from the same subnet. I observed that it used both interfaces to communicate with hosts in the same subnet and gateway, no matter what IP it the source. Packets are distributed round-robin.
I understood what happens when i read this
It's looks ok, until one interface goes down. Half of packets get lost. AIX doesn't "understood" that one of interface died and continue to use it.
Does anyone have any advices?
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2 replies Latest Post - 2011-06-07T11:31:06Z by pavel.alexei
Pinned topic Two interfaces with IP from the same subnet
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Updated on 2011-06-07T11:31:06Z at 2011-06-07T11:31:06Z by pavel.alexei
j.gann 270000SSYT12 PostsACCEPTED ANSWER
Re: Two interfaces with IP from the same subnet2011-06-06T08:38:52Z in response to pavel.alexeithis is what "multipath routing" does (you find this explained in the manuals, also have a look at the aix routing table to get the idea).
anyway, what do want to achieve? network interface redundancy? look at "link aggregation" or "etherchannel", works on layer 2 (ethernet), different alternatives (with or without nw switch configuration / active,active vs. active,backup ) do exist.
if you nevertheless decide you want redundancy at layer 3 (IP), check out "dead gateway detection" (see: ifconfig option "monitor").
pavel.alexei 2700002XMC2 PostsACCEPTED ANSWER
Re: Two interfaces with IP from the same subnet2011-06-07T11:31:06Z in response to j.gannI can "understand" DGD, when we are talking about default gateway or gateway to any external network.
But how to manage DGD for direct connected network? I have en0 192.168.5.21/24 and en1 192.168.5.31/24.
netstat -rn shows:
10.243.5/24 10.243.5.21 U 1 286 en0 - - =>
10.243.5/24 10.243.5.31 U 0 304 en1 - -
both that routing tables are created automatically by the system.
When i unplug cable from en1, AIX doesn't put en1 in down and second route stays alive. This means that server continues to send packets through both interfaces, which results in 50% packet lost.