Linux BNG

Ahad Aboss ahad at swiftelnetworks.com
Sun Jul 15 15:31:07 UTC 2018


Hi Baldur,



Based on the information you provided, CPE connects to the POI via
different service provider (access network provider / middle man) before it
reaches your network/POP.



With this construct, you are typically responsible for IP allocation and
session authentication via DHCP (option 82) with AAA or via Radius for
PPPoE.  You may also have to deal with the S-TAG and C-TAG  at BNG level.
Here are some options to consider;



*Option 1.*



Use Radius for session authentication and IP/DNS allocation to CPE. You can
configure BBA-GROUP on the BNG to overcome the 409x vlan limitation as well
as the S-TAG and C-TAG. BBA-GROUP can handle multiple session. BBA-GROUP is
also a well-supported feature.



Here is an example of the config for your BNG (Cisco router)  ;

===============================================

*bba-group pppoe NAME -1*

 virtual-template 1

 sessions per-mac limit 2

!

*bba-group pppoe NAME -2*

 virtual-template 2

 sessions per-mac limit 2

!

interface GigabitEthernet1/3.100

* encapsulation dot1Q 100 second-dot1q 500-4094*

 no ip redirects

 no ip unreachables

 no ip proxy-arp

 ip flow ingress

 ip flow egress

 ip multicast boundary 30

 *pppoe enable group NAME -1*

 no cdp enable

!

interface GigabitEthernet1/3.200

 encapsulation dot1Q 200 second-dot1q 200-300

 no ip redirects

 no ip unreachables

 no ip proxy-arp

 ip flow ingress

 ip flow egress

 ip multicast boundary 30

 *pppoe enable group NAME -2*

 no cdp enable



Configure Virtual templates too.

===============================================

*Option 2.*



You can deploy a DHCP server using DHCP option 82 to handle all IP or IPoE
sessions.

DHCP option 82 provides you with additional flexibility that can scale as
your customer base grows. You can perform authentication using a
combination of CircuitID, RemoteID or CPE MAC-ADD etc.



I hope this information helps.



Cheers,

Ahad


On Sat, Jul 14, 2018 at 10:13 PM, Baldur Norddahl <baldur.norddahl at gmail.com
> wrote:

> Hello
>
> I am investigating Linux as a BNG. The BNG (Broadband Network Gateway)
> being the thing that acts as default gateway for our customers.
>
> The setup is one VLAN per customer. Because 4095 VLANs is not enough, we
> have QinQ with double VLAN tagging on the customers. The customers can use
> DHCP or static configuration. DHCP packets need to be option82 tagged and
> forwarded to a DHCP server. Every customer has one or more static IP
> addresses.
>
> IPv4 subnets need to be shared among multiple customers to conserve
> address space. We are currently using /26 IPv4 subnets with 60 customers
> sharing the same default gateway and netmask. In Linux terms this means 60
> VLAN interfaces per bridge interface.
>
> However Linux is not quite ready for the task. The primary problem being
> that the system does not scale to thousands of VLAN interfaces.
>
> We do not want customers to be able to send non routed packets directly to
> each other (needs proxy arp). Also customers should not be able to steal
> another customers IP address. We want to hard code the relation between IP
> address and VLAN tagging. This can be implemented using ebtables, but we
> are unsure that it could scale to thousands of customers.
>
> I am considering writing a small program or kernel module. This would
> create two TAP devices (tap0 and tap1). Traffic received on tap0 with VLAN
> tagging, will be stripped of VLAN tagging and delivered on tap1. Traffic
> received on tap1 without VLAN tagging, will be tagged according to a lookup
> table using the destination IP address and then delivered on tap0. ARP and
> DHCP would need some special handling.
>
> This would be completely stateless for the IPv4 implementation. The IPv6
> implementation would be harder, because Link Local addressing needs to be
> supported and that can not be stateless. The customer CPE will make up its
> own Link Local address based on its MAC address and we do not know what
> that is in advance.
>
> The goal is to support traffic of minimum of 10 Gbit/s per server. Ideally
> I would have a server with 4x 10 Gbit/s interfaces combined into two 20
> Gbit/s channels using bonding (LACP). One channel each for upstream and
> downstream (customer facing). The upstream would be layer 3 untagged and
> routed traffic to our transit routers.
>
> I am looking for comments, ideas or alternatives. Right now I am
> considering what kind of CPU would be best for this. Unless I take steps to
> mitigate, the workload would probably go to one CPU core only and be
> limited to things like CPU cache and PCI bus bandwidth.
>
> Regards,
>
> Baldur
>
>


-- 
Regards,

Ahad
Swiftel Networks
"*Where the best is good enough*"


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