8 BRAS L2 DHCP Radius Proxy Example

Description

BRAS DHCP L2 mode means that the subscriber recieves an IP-address via DHCP Proxy and proceeds to ААА in the Billing system. Then the subscriber is terminated by VAS Experts DPI and transferred to border equipment.

The following elements are involved in the VAS Experts DPI operation scheme in BRAS L2 DHCP Radius Proxy mode:

Client with Q-in-Q access type

FastDPI - traffic processing and policing

FastPCRF - proxying requests between fastDPI and Radius

Radius server - accepts requests from fastPCRF and generates responses with specified attributes

Router - is responsible for packets transmission to the Internet and the backward routing. It is necessary to specify the Static Route, since VAS Experts DPI does not support OSPF and BGP at the moment.

Scenario

FastDPI Setup

Editing the DPI Configuration File

First, you need to uncomment (add) the following lines to the /etc/dpi/fastdpi.conf configuration file.

#enabling internal database of user properties
udr=1
#enabling the authorization by IP mode
enable_auth=1
#enabling L2 BRAS mode
bras_enable=1
#"virtual" IP address of DPI (must be unique on the network)
bras_arp_ip=192.168.1.2
#"virtual" MAC address of DPI (use the real MAC address of any of the DNA interfaces)
bras_arp_mac=a0:36:9f:77:26:58
#IP address of the border
bras_gateway_ip=192.168.1.1
#MAC address of the interface to which DPI is connected on the border
bras_gateway_mac=c4:71:54:4b:e7:8a
#server data which Fastpcrf is installed on (if it is the same where Fastdpi is installed, do not change)
auth_servers=127.0.0.1%lo:29002
#enabling of DHCP Relay Agent mode
bras_dhcp_mode=1
#192.168.10.2 – IP-address of DHCP-server
#veth0 – the name of the network interface that communicates with the DHCP server
#67 – port, default value: 68
#arp_proxy - lag in response to ARP requests for the DHCP-server IP-address
#alias_ip - DHCP server alias
#reply_port - port that recieves for responses from the DHCP server
bras_dhcp_server=192.168.10.2%veth0:67;arp_proxy=1;alias_ip=192.168.1.4;reply_port=67
#vlan termination (in this case the tag will be cut out)
bras_vlan_terminate=1
#MAC spoofing
bras_terminate_l2=1
#local traffic interconnection
bras_terminate_local=1
#enabling accounting
enable_acct=1
#subscribers billing statistics
netflow=4
#timeout for sending statistics
netflow_timeout=60

You should set your own values for the following parameters bras_arp_ip bras_arp_mac bras_gateway_ip bras_gateway_mac

AS Specification for Termination

The next step is to mark the AS traffic that has to be terminated.

The AS list is prepared in text format, each entry on a new line in the format CIDR<space>AS_number:

192.168.2.0/24 65550

Then it is converted into an internal format by the as2bin utility and placed in the file /etc/dpi/aslocal.bin, where DPI will pick it up. The address ranges specified in the list will be added to the global list.

cat aslocal.txt | as2bin /etc/dpi/aslocal.bin

The list of local AS to be terminated is prepared in a text file in the format AS_number<space>flag:

65550 local
65550 term

To convert into internal format and place into the main directory, where the DPI will pick the settings up:

cat my_as_dscp.txt | as2dscp /etc/dpi/asnum.dscp

FastPCRF Setup

To configure FastPCRF, edit the file /etc/dpi/fastpcrf.conf. Find the line with the RADIUS server parameters and change

#secret123 - Radius secret
#192.168.1.10 - IP address of Radius server
#eth0 - the interface from which FastPCRF communicates with the Radius server
#1812 - the port to which FastPCRF sends authorization requests
#acct_port - the port that FasPCRF sends Accouting to
radius_server=secret123@192.168.1.10%eth0:1812;acct_port=1813

Radius Setup

The setup is given as an example on freeRADIUS 3 and may differ from the configuration of your Radius server.

VasExperts Dictionary

First you need to add a VSA dictionary

Copy the dictionary /usr/share/dpi/dictionary.vasexperts from the fastpcrf distribution into $freeRadius/share/freeradius directory

Add the following line to the main dictionary $freeRadius/share/freeradius/dictionary:

$INCLUDE dictionary.vasexperts

Creating Radius Client

Add the following lines to raddb/clients.conf of the Radius server

client fastdpi1 {
ipaddr	= 192.168.1.5
secret	= secret123
require_message_authenticator = yes
#	add_cui = yes
virtual_server	= fastdpi-vs
}

Creating a virtual server

To create a virtual server configuration, copy the included in the FreeRadius file raddb/sites-available/default, to raddb/sites-enabled/fastdpi-vs. Then edit fastdpi-vs:

set the name of the virtual server - change the 'server default' line at the beginning of the file to 'server fastdpi-vs'

in the 'listen' section for auth requests (type = auth), set IP-addresses and ports that will listen to the incoming requests (note that this is the local address of the Radius server):

ipaddr = 192.168.1.10
port = 1812
interface = eth0

Creating an account for authorization

Add subscriber data to the file /etc/raddb/users

testuser Cleartext-Password := "VasExperts.FastDPI"
Framed-IP-Address = 192.168.2.199,
VasExperts-DHCP-DNS = 8.8.8.8,
VasExperts-Enable-Service = "9:on",
VasExperts-Policing-Profile = "100Mbps"
VasExperts-Service-Profile = "11:user_nat"

Two more lines for FastPCRF should also be added to the file /etc/raddb/users

VasExperts.FastDPI.unknownUser Cleartext-Password := "VasExperts.FastDPI"
DEFAULT	Cleartext-Password := "VasExperts.FastDPI"

Router Setup

On the router, add a static route to the subnet served by the VAS Experts DPI.

/ip route add dst-address=192.168.2.0/24 gateway=192.168.1.2

Connecting a Test Subscriber

When an unknown subscriber is connected, FastPCRF sends an Access-Request with the following content:

User-Name = "A0:36:9F:77:26:58"
User-Password = "VasExperts.DPI"
Calling-Station-Id = "a0:36:9f:77:26:58"
NAS-Port-Type = 5
NAS-Port = 100
NAS-Identifier = "VasExperts.FastDPI"
Service-Type = 2
VasExperts-Service-Type =1
VasExperts-DHCP-Request = Discover
VasExperts-DHCP-RelayRemoteId = 0x3137322e31372e312e32
VasExperts-DHCP-RelayCurcuitId = 0x000601360100000a

By default FastPCRF puts the subscriber's MAC address in the User-Name field. In the FastPCRF configuration file it is possible to specify what should be used as a login (for example, QinQ tag)

При успешной авторизации данного абонента FastPCRF помимо сетевых параметров также ожидает получить список необходимых услуг и тарифный для данного абонента в Access-Accept When the subscriber is authorized successfully, FastPCRF expects to receive a list of necessary services and a tariff for this subscriber in Access-Accept in addition to other network parameters.

Session-Timeout = 84600
User-Name = "Subscriber001"
Framed-IP-Address = 10.0.0.10
Framed-IP-Netmask = 255.255.255.0
VasExperts-DHCP-Gateway = 10.0.0.1
VasExperts-DHCP-DNS = 8.8.8.8
VasExperts-DHCP-DNS = 8.8.4.4
VasExperts-Policing-Profile = "100Mbps"
VasExperts-Service-Profile = "11:CG_NAT_POOL_1"
VasExperts-Service-Enable = "9:on"

Troubleshooting

When implementing L2 BRAS, some errors may occur, when the subscribers cannot be authorized and connected to the Internet. Below are the most common problems:

There are no authorization requests

Check if fastPCRF process is running and if the server Radius address is specified correctly.

Authorization requests do not reach the Radius server

Check if the Firewall's port is allowed to receive authorization requests (by default 1812) on the Radius server.

I can ping DPI, but the ping does not reach the border

It is necessary to set a static route towards the subscribers on the border. Since DPI is not able to announce the subscriber subnets that it serves yet, it is necessary to indicate the border where to route the traffic.

In the case of using NAT for subscribers, a similar route is required for the subnets used in NAT.

Сheck if the parameters bras_gateway_ip and bras_gateway_mac are set correctly.

Statistics for Accounting is not sent

Check if the port for receiving statistics is allowed in the Firewall (by default 1813) on the Radius server.

Check if service 9 is activated for the subscriber.

Check if accounting is enabled in DPI configuration settings.

Check if the correct value is specified for the Netflow parameter.

CoA does not reach BRAS

Check if the port for receiving CoA (3799 by default) is allowed in the Firewall on the server with FastPCRF.