[AusNOG] Spreading the load of ISP customers at Layer2

[Joseph Goldman]

With have the same gateway IP universal across routers - I can't really 
help with that, and if you've got a 'hack' that is working, perhaps 
stick with that.

  In regards to sharing load between mikrotiks, assuming you are using 
DHCP server (IPoE, since you specified no PPPoE) - my solution would 
require a remote agent to use Mikrotiks API in x increments to gather 
number of subscribers per router, then adjust delay-threshold (or 
authoritative setting) to delay accordingly to the lowest subscriber 
count Tik so it responds first. It is a definite hack-about but should 
still achieve what you are after. I'd also be interested in just leaving 
them all the same and letting general network fluctuations decide which 
response it gets first and uses, but that has a higher possibility of 
them stacking on one.

------ Original Message ------
From: "Damian Ivereigh" <damo at launtel.net.au>
To: "ausnog at ausnog.net" <ausnog at ausnog.net>
Sent: 13/09/2021 7:23:36 PM
Subject: [AusNOG] Spreading the load of ISP customers at Layer2

>Hi guys,
>
>We have built all our ISP infrastructure based on the NBN style doubled tagging of services - in other words each subscriber circuit comes through on it's own ctag. This makes separating everything really easy because we pipe each vlan through to different BNG's. However we are now presented with a wholesaler who does not separate each circuit, but instead just bridges them all together into a single circuit. We can distinguish each circuit only by inspecting the DHCP Option82 so that we can allocate the right IP address, which is fine, but it is hard to allocate them to use a particular BNG to send and receive traffic.
>
>By the way I am not talking dynamic load balancing just having multiple BNG with a subsection of the customers on each one - load sharing?
>
>Until now with double tagging, we can reuse the same gateway IP address (i.e. the side facing the customer) on all the BNG and because each BNG only sees it's circuits, it will only respond to arps that it should do on the vlans assigned to it. However with all the customers on the same circuit it is impossible for multiple BNG to have the same IP address without creating all sorts of duplicate arps etc. We could turn off arp on all but one of the BNG and then put up with the asymmetric routing (makes reverse path filtering impossible) - i.e. send all upload traffic through a single BNG, but download comes from different ones (according to what BNG they are allocated to).
>
>I have come up with another hack by using essentially using arp spoofing where we get a separate box to respond to the arp requests based on what the source IP is, but I can't help wondering how others have handled this. The wholesaler tells me there are other ISPs with 5000+ services on the single circuit (feels like a recipe for a broadcast storm to me).
>
>Oh and no we don't want to use PPPoE :-)
>
>Ideas anyone?
>
>Damian
>
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