I'm setting up a media server at home with an old PowerMac that I found rotting in some cellar (great computer by the way, I don't understand why they wanted to throw it away) and I installed Debian Jessie on it for this purpose. I also set up Avahi to make it discoverable by other computers on the network and everything is working fine.

My problem arises from the fact that the computer has two network cards, one of which is a Gigabit Ethernet card and one that supports only Fast Ethernet. Because my home router is pretty old and crappy it has only 100BaseT Ethernet ports and 802.11g WiFi, which makes the Gigabit network card pretty much useless.

To make the wider bandwith of some use (as a workaround until I buy a decent router), I thought to connect the PowerMac to the router through the slow card and connect the fast one directly to my iMac (where I'd have the most benefit from the higher speed). After adjusting the network settings I've been able to get the link working and as a result I can access the PowerMac from two IPs on the other computer.

network diagram showing the described connections

My doubt is: which interface will be used when connecting to it through its Bonjour name? I know for sure that the iMac knows both addresses and the output of dns-sd proves that:

$ dns-sd -Q powermac.local

DATE: ---Sat 31 Aug 2013---
20:02:55.800  ...STARTING...
Timestamp     A/R Flags if Name                          Type  Class   Rdata
20:02:55.927  Add     2  4 PowerMac.local.               Addr   IN
20:02:56.017  Add     2  5 PowerMac.local.               Addr   IN

But how can I be sure that every time I access PowerMac.local the system selects the best IP address? In this example it's the first one listed by dns-sd, but it isn't always the case and I don't know how to explicitly tell to the software to use one of them.

EDIT: Regarding Danila's answer, I found this command through a quick search, is it the correct command? (eth1 is the Gigabit card)

route add -net netmask dev eth1
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  • How is the iMac connected to the router? If the gigabit to the powermac is its only connection then surely the packets will have to always go to the right adaptor as that's the only one it can reach? I'm guessing the doubt is because there's a loop through wifi, but you haven't said. – Tim Abell Jan 20 '14 at 1:10
  • Yes, the iMac was also connected to the Wi-Fi network because it needed access to the Internet (maybe you should update the schematic to represent it). But since then I bought a new router with Gigabit Ethernet and 802.11n Wi-Fi so I don't need this anymore ;) – EliaCereda Jan 20 '14 at 15:29

Since all networking in linux kernel by default is weak host model, you will have to put static routes in your Debian, so every time your iMac sends a packet it gets processed by 1G NIC.

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  • Thanks, however could you elaborate a little your answer? Basically, how would I do that? – CrazyMonster Aug 31 '13 at 20:13
  • Sure, I'm on my way. ;) – CrazyMonster Aug 31 '13 at 20:17
  • It might be just me but your answer made no sense at all to me. Would you mind making it clearer? – Tim Abell Jan 19 '14 at 23:32
  • That means that if hop behind (router e.t.c.) routes the packet to the server and has both routes to that server interfaces in its table (eth1 -, eth2 - and packet it is routing in its header has DST_IP for eth2 IP (192.168.2.x) it is not garaunteed that packet will get recieved by eht2 interface as in weak host model IP ADDR is not associated with the interface, but rather with the host. I hope this helps. – Danila Ladner Jan 20 '14 at 0:33
  • Okay, so the first thing that tripped me up is I hadn't heard of "weak host model" as a technical term. I learned something - en.wikipedia.org/wiki/Host_model – Tim Abell Jan 20 '14 at 0:59

Transfer a big file across, and if the transfer rate is at gigabit levels then don't worry about it as it's working fine? (If it ain't broke don't fix it)

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    It did, I never really understood WHY it worked, though. I never explicitly told it to do so but the iMac always chose the correct connection. Does it check the speed of the link when it has to choose between two IP addresses? – EliaCereda Jan 20 '14 at 15:32
  • I guess it's assigning a lower "metric" number to routes on the gigabit link. en.wikipedia.org/wiki/Metrics_(networking) – Tim Abell Jan 20 '14 at 20:06
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    Oh, i see... Well, it's nice to know! Also, I'm curious about what you used to create the schematic in the question... Is it a standard? – EliaCereda Jan 21 '14 at 21:36
  • No problem. I just drew pretty pictures with Dia wiki.gnome.org/Apps/Dia and made no attempt to follow any standards :-) – Tim Abell Jan 22 '14 at 1:41

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