1. Labcourse “Routerlab”
Customer Access

2. The big picture Phone Network Phone Exchange Point of Presence
Core Network
ATM Network
PPP-AC
DSLAM
Core Routers
Access Router
DSL Router
Customer Datacenter
Datacenter
Modem
Splitter
Home Network

3. Accessing the Net PPPoE Connection ATM Circuit IP Data Phone Exchange
Point of Presence
Core Network
ATM Network
PPP-AC
DSLAM
Core Routers
Access Router
DSL Connection
DSL Router
Customer Datacenter
Datacenter
Modem
Big picture, real network…
Animation:
Setup ATM circuit between DSLAM and PPP-AC
Setup DSL Link, modem synchronization
Dial-up: Setup PPP Connection
3a) PPP-AC hands over authentication data to RADIUS Server during PPP Handshake
4) IP Data possible
Splitter
RADIUS
Auth. Request
Home Network

4. PPP – Point-to-Point Protocol
Encapsulates other protocols (tunnel)
Enables AAA (authentication, authorization, accounting)
Supports auto-configuration
We consider IP over PPPoE (PPP over Ethernet)

5. Phases of PPP No Link Yes Authentication Link Establishment Yes Phase
Established
successful?
Need
authentication?
Link
Establishment
Phase
Authentication
Phase
Yes
Link
Dead
Yes No
Phases of a PPP Connection,
Start at Link-DEAD.
Authentication is optional
Authentication
successful?
Link
Termination
Phase
Network-Layer
Protocol Phase
Yes No

6. PPPoE Frame Ethernet Frame Dst. Addr Src. Addr Type PPPoE Data
0x8863: PPPoE Discovery
0x8864: PPPoE Session
Ethernet Frame
Data
Dst. Addr
Src. Addr
Type
PPPoE
0x00: Data
0x07: PADO
0x09: PADI
0x19: PADR
0x65: PADS
0xa7: PADT
Always 0x1
Always 0x1
Announced in PADS Frame,
before: 0x0000
Version
(4 Bit)
Type
(4 Bit)
Code
(1 Byte)
Session-ID
(2 Byte)
Length
(2 Byte)
PPP Protocol
(2 Byte)
Layout of a PPPoE Frame:
Animation: Contents of Fields appear
Payload Length in Bytes
0x0021: IP
0x8021: IP Control Prot. (IPCP)
0xc021: Link Control Prot. (LCP)
0xc023: Password Auth. Prot. (PAP)
0xc223: Challenge Handshake
Auth. Prot. (CHAP)
Payload
(variable)

7. PPPoE Session DSL-AC Client
PPPoE Active Discovery (AD) Initiation: PADI
Broadcast Packet, optional: Service-Name
PPPoE AD Offer: PADO
Service-Name, AC-Name
If multiple PADO:
Choose one
PPPoE AD Request: PADR
Service-Name, AC-Name
PPPoE AD Session Confirmation: PADS
Session-ID
PPP Session
PPP Session handshake (LCP), including authentication
IP configuration (IPCP)
IP Session (Payload)
Set local IP configuration
Authenticate user and
authorize session
PPPoE AD Termination
Can be sent by either side
Record
accounting data

8. RADIUS “Remote Authentication Dial-In User Service”
Central RADIUS Server
Provides authentication service for Network Access Servers (NAS)
NAS: Every device that a user can use to connect to a network, e.g:
PPP-AC, WPA access-point, x switch

9. PPP Session with RADIUS
Client
PPP-AC/NAS
Auth. Server
LCP: Conf Request
Auth. Proto: PAP
LCP: Conf Ack
Auth. Proto: PAP
RADIUS: Access Request
Username + Password
PAP: Auth Request
Username + Password
RADIUS: Access Accept
Attributes:
IP Address ….
PAP: Auth Ack
Username + Password
IPCP: Conf Req.
IP:
RADIUS: Accounting Start
Attributes:
IP Address
Session ID ….
Sample PPP Session.
Note the IPCP Conf Reject: Server rejects IP “ ” and proposes the real one.
IPCP: Conf Reject
IP:
Write accounting
record
RADIUS: Accounting Stop
Attributes:
Session ID
Duration,Traffic Volume …
LCP: Terminate Link
Write accounting
record

10. Excurse: Other providers
Point of Presence
Datacenter
Core Network
PPP-AC
Access Router
Phone Exchange
Point of Presence
Core Network
ATM Network
First: Reseller: Setup own RADIUS server, use complete infrastructure otherwise
Own Core: Route some traffic though own core
Own Core2: Route all traffic through own core, get IP directly from PoP
Own PoP: Build own PoP. Switch ATM Circuit from DSLAM to own PPP-AC
Colocate DSLAM: Setup own DSLAM in Phone Exchange, rewire phoneline to that DSLAM
Not shown: own Phoneline
PPP-AC
DSLAM
Core Routers
Access Router
DSL Router
Customer Datacenter
Datacenter
Modem
Splitter
Home Network

11. The smaller picture Phone Network Point of Presence loadgen10X
Phone Exchange
Point of Presence
Core Network
ATM Network
PPP-AC
DSLAM
Core Routers
Access Router
DSL Router
Customer Datacenter
Datacenter
Modem
Going from the big picture to the real routerlab configuration
No phones, no phone network
No DSLAM, No Modem, No ATM network, direct connection from DSL Router to PPP-AC
Data-Center simplified: Just one loadgen acting as webserver
No CoreNetwork: this has been done before.
5 RADIUS server installed on the same machine as the PPP-AC
Splitter
Home Network

12. The smaller picture Point of Presence loadgen10X rj1 PPP-AC
Access Router
DSL Router
Customer Datacenter
Loadgen103
VLAN 102
Home Network