IP Tunneling

Generic Routing Encapsulation (GRE)
Point-to-Point Tunneling Protocol (PPTP)
Layer Two Tunnel Protocol (L2TP)
Ascend Tunnel Management Protocol (ATMP)
Mobile IP
Layer Two Forwarding (L2F)
Rate Based Satellite Control Protocol (RBSCP)
Bisync Serial Tunnelling (BSTUN)
X25 Over TCP (XOT)
Serial Tunneling - Synchronous Data Link Control (STUN-SDLC)
Serial Tunnel (STUN)

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Technology Information
- Point-to-Point Tunneling Protocol (PPTP)
  - PPTP Frequently Asked Questions 24-Mar-2009
- Mobile IP
  - Introduction to Mobile IP 05-Oct-2001
- Access Control Lists and IP Fragments 10-Aug-2005
Design
- Layer Two Tunnel Protocol (L2TP)
  - Access VPDN Dial-in Using L2TP 03-Jul-2001
  - Access VPDN Dial-in Using IPSec Over L2TP 17-Nov-2000
Configuration
- Generic Routing Encapsulation (GRE)
  - Next Generation Multicast Default MDT: Profile 0 09-Apr-2018
  - Multicast over a GRE Tunnel 23-Jun-2016
  - Configuring a GRE Tunnel over IPsec with OSPF 26-Sep-2008
  - IPSec/GRE with NAT on IOS Router Configuration Example 29-Aug-2008
  - Configuring Dynamic Multipoint VPN Using GRE Over IPSec With EIGRP, NAT, and CBAC 14-Jan-2008
  - Configuring Router-to-Router IPsec (Pre-shared Keys) on GRE Tunnel with IOS Firewall and NAT 06-Feb-2007
  - Configuring Dynamic Multipoint VPN Using GRE Over IPsec With OSPF, NAT, and Cisco IOS Firewall 30-Nov-2006
  - Configuring IPSec with EIGRP and IPX Using GRE Tunneling 21-Jun-2005
- Layer Two Tunnel Protocol (L2TP)
  - Set Up L2TP Tunnel Between a Windows Machine and a Cisco Router 11-May-2016
  - Client-Initiated L2TPv2 Tunnel with ISR4000 That Acts as a Server Configuration Example 18-Nov-2014
  - L2TPv3 over FlexVPN Configuration Guide 06-Jun-2013
  - Configuring Layer 2 Tunnel Protocol Authentication with RADIUS 14-May-2009
  - Configuring Layer 2 Tunneling Protocol (L2TP) over IPSec 19-Jan-2006
- Point-to-Point Tunneling Protocol (PPTP)
  - Configuring the Cisco Router and VPN Clients Using PPTP and MPPE 01-Feb-2007
- Serial Tunnel (STUN)
  - Guide to BSC and BSTUN 29-Sep-2014 (ZIP - 71 KB)
- X25 Over TCP (XOT)
  - TCP over X.25 23-Oct-2018
  - X25 Over TCP/IP With XOT Keepalives 10-Mar-2006
  - X.25 over TCP/IP 01-Jun-2005
- Generic Routing Encapsulation (GRE)
  - WCCP on ASA: Concepts, Limitations, and Configuration 31-May-2013
Operation and Troubleshooting
- Applicable to Multiple Technologies
  - How Virtual Private Networks Work 13-Oct-2008
  - Cisco Hardware and VPN Clients Supporting IPSec/PPTP/L2TP 07-Feb-2007
- Generic Routing Encapsulation (GRE)
  - Understand GRE Tunnel Keepalives 18-Apr-2025
  - Configure BGP over DMVPN Phase 3 14-Nov-2024
  - Determine What Impacts GRE Tunnel Interface States 18-Oct-2023
  - Configure L2 Bridging across an L3 Network 28-Jul-2023
  - Quality of Service Options on GRE Tunnel Interfaces 20-Mar-2015
  - Overview of Keepalive Mechanisms on Cisco IOS 17-Dec-2014
  - DMVPN Phase 1 Debugs Troubleshoot Guide 16-Jan-2014
  - How GRE Keepalives Work 16-Jun-2006
  - Intermediate System-to-Intermediate System (IS-IS) TLVs 10-Aug-2005
  - Why Can't I Browse the Internet when Using a GRE Tunnel? 10-Aug-2005
- Layer Two Tunnel Protocol (L2TP)
  - Validate Layer 2 Hardware on Catalyst 9000 Series Switches 24-Jul-2024
  - Xconnect over VRF Aware L2TPv3 in ASR1K 03-Apr-2018
  - L2TP in StarOS - Implementation on the ASR5k and Troubleshoot L2TP Peering - L2TPTunnelDownPeerUnreachable 21-Mar-2016
- Mobile IP
  - Troubleshoot Mobile IP Tunnel Establishment 24-Jul-2023
- Serial Tunnel (STUN)
  - Guide to BSC and BSTUN 29-Sep-2014 (ZIP - 71 KB)
  - Configuring and Troubleshooting Serial Tunneling (STUN) 09-Sep-2005
- Understanding the authentication imsi-auth | msisdn-auth Configuration for Corporate L2TP APNs 25-Apr-2017