5K subscribers on a single port/handover VLAN for any modern BNG should
not be a problem...
Assuming you're sticking with IPoE/DHCP and you really want to split
subscribers over multiple BNGs, I'd do something like this:
1. Present the backhaul VLAN to your N BNGs. You will need to use unique
IP addresses on the subscriber-interfaces (or equivalent depending on
your vendor).
2. Configure the BNGs for DHCP relay or DHCP-to-RADIUS proxying (or
equivalent).
3. Since DHCP will be broadcast, all BNGs should receive the
DHCPDISCOVER from the client and relay/proxy it to your DHCP/RADIUS servers.
4. Based on Option-82 information, have your DHCP/RADIUS servers return
a DHCPOFFER/RADIUS Access-Accept only for the BNG you *want* to serve
the client. That should bring up subscriber management on the specific
BNG and ensure you have symmetric traffic flows for that subscriber.
You might have to deal with the other BNGs generating logs for the
session failing to establish on them (no DHCPOFFER or RADIUS response,
or maybe you could send an Access-Reject or something).
Depending on how the N:1 VLAN is configured, you may need to be cautious
with local-proxy-arp to ensure that only the active BNG responds for
subscriber ARPs.
There should be no problems with broadcast storms - assuming the
wholesaler is using N:1 split-horizon/forced-forwarding to prevent
sub-to-sub communication at L2.
There are other ways to solve for this, but I'm not sure why you'd want
to make this much more complex :-).
AJ
<I haven't done BNG stuff for 7 or 8 years, but I'm fairly confident
this will work - at least on the platforms I'm most familiar with>
On 9/13/21 2:23 AM, Damian Ivereigh wrote:
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
_______________________________________________
AusNOG mailing list
AusNOG@lists.ausnog.net
http://lists.ausnog.net/mailman/listinfo/ausnog
