Cisco IOS WAN Layer 2 cheat sheet: PPP (Point-to-Point Protocol) with CHAP authentication, and Frame-Relay — multipoint and point-to-point sub-interface configurations.
PPP — Point-to-Point Protocol
PPP with CHAP Authentication
| Command | Description |
|---|---|
| hostname Router1 | Set hostname (used for CHAP authentication) |
| username Router2 password cisco123 | Create account for the remote router (on Router1) |
| int ser9/0 | Enter serial interface |
| ppp authentication chap | Require CHAP authentication from the remote router |
| debug ppp authentication | Debug PPP authentication process |
PPP is a point-to-point environment — no Layer 2 addresses (MAC) are used.
Frame-Relay — Basic Setup
Simple Frame-Relay Link
| Command | Description |
|---|---|
| int ser9/0 | Enter serial interface |
| encapsulation frame-relay | Set L2 encapsulation to Frame-Relay |
| ip address 192.168.0.1 255.255.255.0 | Assign IP to the interface |
| frame-relay map ip 10.1.1.1 110 broadcast | Manually map neighbor IP to DLCI 110 (when InverseARP is not working) |
Frame-Relay — Multipoint Sub-Interface (Hub)
Used when one physical interface connects to multiple remote sites. Inverse ARP is disabled — manual mapping required.
Multipoint Frame-Relay (Hub Router)
| Command | Description |
|---|---|
| interface serial 0/0 | Physical serial interface |
| no ip address | Remove IP from physical interface |
| encapsulation frame-relay | Set Frame-Relay encapsulation |
| interface serial 0/0.1 multipoint | Create multipoint sub-interface |
| ip address 10.0.1.1 255.255.255.0 | Assign IP to sub-interface |
| frame-relay map ip 10.0.1.2 100 broadcast | Map first spoke router IP → DLCI 100 |
| frame-relay map ip 10.0.1.3 200 broadcast | Map second spoke router IP → DLCI 200 |
Spoke routers in multipoint topology do not need a sub-interface.
Frame-Relay — Point-to-Point Sub-Interfaces (Hub)
Each spoke gets its own sub-interface. Cleaner, avoids split-horizon issues with routing protocols.
Point-to-Point Frame-Relay (Hub Router)
| Command | Description |
|---|---|
| interface serial 0/0 | Physical interface |
| no ip address | Remove IP from physical interface |
| encapsulation frame-relay | Set Frame-Relay encapsulation |
| interface serial 0/0.100 point-to-point | Sub-interface for first spoke (DLCI 100) |
| ip address 10.0.1.1 255.255.255.0 | IP for this p2p link |
| frame-relay interface-dlci 100 | Assign DLCI 100 to this sub-interface |
| interface serial 0/0.110 point-to-point | Sub-interface for second spoke (DLCI 110) |
| ip address 10.0.2.1 255.255.255.0 | IP for this p2p link |
| frame-relay interface-dlci 110 | Assign DLCI 110 to this sub-interface |
Spoke routers in p2p topology must also create a point-to-point sub-interface.
Frame-Relay Diagnostics
show commands
| Command | Description |
|---|---|
| show frame-relay pvc | Show PVC status and traffic counters |
| show frame-relay map | Show IP-to-DLCI mapping table |
Cisco IOS Command Reference | PPP & Frame-Relay