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Rich Freeman <rich0@g.o> writes: |
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> On Fri, Dec 25, 2015 at 9:00 PM, Adam Carter <adamcarter3@×××××.com> wrote: |
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>>> grandstream.yagibdah.de (192.168.3.80) auf 00:0b:82:16:ed:9e [ether] auf |
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>>> enp2s0 |
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>>> grandstream.yagibdah.de (192.168.3.80) auf 00:0b:82:16:ed:9e [ether] auf |
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>>> enp1s0 |
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>>> spa.yagibdah.de (192.168.3.81) auf 88:75:56:07:44:c8 [ether] auf enp2s0 |
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>>> spa.yagibdah.de (192.168.3.81) auf 88:75:56:07:44:c8 [ether] auf enp1s0 |
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>>> |
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>>> |
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>>> enp2s0 is an interface dedicated to a PPPoE connection, and enp1s0 |
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>>> connects to the LAN. |
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>>> |
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>>> IIUC, this is bound to cause problems. |
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>>> |
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>>> How is it possible for the wrong entries to be created, and what can I |
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>>> do to prevent them? |
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>>> |
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>> |
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>> arp mappings are untrusted so your machine will accept anything is sees on |
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>> the network. That's what makes MITM so easy on a connected subnet. What |
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>> makes you think they are wrong? Also, the output of ifconfig would be |
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>> helpful. |
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> |
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> I suspect those interfaces are getting bridged or something, but I'm |
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> not an expert on such things. |
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No physical interface is connected to the bridge interface, though |
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selected traffic from the devices can reach one of the VMs that are |
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connected to the bridge. |
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> If a given IP has a MAC on more than one interface, the interface the |
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> packets go out to is still controlled by the routing rules. If the |
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> routing rule says that 1.1.1.1 is on eth0 it doesn't matter that eth0 |
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> doesn't have an ARP entry and eth1 does - I believe it will just be |
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> undelivered or sent to the gateway for eth0 if it isn't on a local |
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> subnet for that interface. |
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There are no arp entries created for interfaces of the host. No traffic |
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from the devices can make it to enp2s0. |
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> If you have some kind of routing loop it could actually make its way |
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> back to the interface on eth1. |
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The traffic would have to be routed back via enp2s0 from somewhere. |
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Since traffic from the devices doesn't go over enp2s0, it cannot be |
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routed back there. |
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> ARP doesn't come into play until the kernel goes to send something on |
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> an interface and determines it is on a subnet for that interface. |
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The devices are not on a subnet of the interface, hence no arp entries |
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for them should be created for that interface. |
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> Again, I'm not an expert in this and there could be some nuance to the |
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> rules that I'm missing. |
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Me neither ... The devices are functional, though I can't tell if |
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traffic from or to them can be misdirected because of the arp entries |
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that shouldn't exist. The devices might still work if some of their |
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traffic is misdirected, just not as well as they otherwise could. |
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Since they are VOIP devices, they are required to work well --- and the |
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VOIP quality is actually not good enough. So I'm looking for possible |
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causes, and wrong arp entries might be one. |
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