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Re: dual port cross over cable bonding


On Fri, Oct 05, 2018 at 03:14:15PM +0100, Adam Weremczuk wrote:
> Hello,
> I have 2 servers running Proxmox 5.2 (based on Debian 9).

Have you considered using OpenVSwitch for the task?

> I've connected Ethernet ports between them with a pair of cross over cables.


> iface ens1f0 inet manual
> iface ens1f1 inet manual

Not needed. ifupdown is smart enough to bring those up without these

> auto bond1
> iface bond1 inet static
>     slaves ens1f0 ens1f1

It's 'bond-slaves', not 'slaves'

>     address
>     netmask
>     bond_miimon 100
> #    bond_mode 802.3ad
>     bond_mode balance-rr
>     bond_xmit_hash_policy layer3+4

Documentation/networking/bonding.txt.gz clearly states that:


    Selects the transmit hash policy to use for slave selection in
    balance-xor, 802.3ad, and tlb modes.

balance-rr and xmit_hash_policy do not play together.

> Tried both 802.3ad and balance-rr modes.

And predictably 802.3ad did not work for you.
You're using cross-cable = you lack LACP Partner.
No LACP probes = 802.3ad fails.

> AFAIK only these 2 provide link aggregation.

No. There is 'balance-tlb' that does it too, but it's useless in
cross-over setup.
Add any cheap unmanaged switch to the picture, and it will be different.

> Unfortunately in either mode cross pinging fails with "Destination Host Unreachable".

Leaving aside '802.3ad' that will never work for you, let's focus on

Starting with something simple, have you confirmed via tcpdump that both
links receive ICMP from the other host?

> The same configuration works fine against managed switch ports (LACP/LAG).

Adding a hint here, OpenVSwitch can be LACP Partner. Linux kernel can be
Actor only.

> So my question is why this is not working and whether it's possible at all?

802.3ad - both hosts are unable to negotiate links for ingress traffic.
balance-rr - my best guess so far goes into ARP filtering direction.


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