1. Junos Intermediate Routing
Chapter 6: IP Tunneling

2. Chapter Objectives
After successfully completing this chapter, you will be able to:
Describe IP tunneling concepts and applications
Explain the basic operations of GRE and IP-IP tunnels
Configure and monitor GRE and IP-IP tunnels

3. Agenda: IP Tunneling Overview of IP Tunneling GRE and IP-IP Tunnels
Implementing GRE and IP-IP Tunnels

4. What Is an IP Tunnel?
An IP communications channel between two networks over an IP network (typically the Internet)
Can be secure or unsecure, depending on tunneling protocol
Internet
Customer X
Site-A
Customer X
Site-B

5. Tunneling IP Packets
When a packet enters an IP tunnel, it is encapsulated; once it exits the tunnel, it is decapsulated
Tunnel Endpoint A
Internet
Tunnel Endpoint B
Rtr X
User A
User B
Encapsulated Packets
Payload Packet
Payload Packet
Outer IP Header
Tunnel Header
IP Header
Inner IP Header
IP Header
IP Payload
IP Payload
IP Payload

6. Uses of IP Tunnels (1 of 2)
IP tunnels can carry traffic that is not otherwise routable over a public IP network such as the Internet
This traffic could include IPX, AppleTalk, or IP traffic that uses RFC 1918 addressing
Internet
Company X
Site-A
Company X
Site-B
IPX
IPX
IP Tunnel
AppleTalk
AppleTalk
RFC 1918
RFC 1918

7. Uses of IP Tunnels (2 of 2)
IP tunnels can be used as backup links if failure occurs
Use route preference or metrics to prefer internal connection over IP tunnel when the network is stable
Internet
Note: Traffic from Subnet A to Subnet B uses primary path between R1 and R2 when it is available; otherwise the IP tunnel is used.
Tunnel functions as a point-to-point link between R1 and R2 R1 R2
Subnet A
Subnet B

8. Agenda: IP Tunneling Overview of IP Tunneling GRE and IP-IP Tunnels
Implementing GRE and IP-IP Tunnels

9. Overview of GRE and IP-IP
GRE is an IP tunneling protocol that can encapsulate a wide variety of Network Layer protocol packet types
IP-IP is an IP tunneling protocol that can encapsulate one IP packet inside another IP packet
IPX
Internet
IPX
Outer IP Header
AppleTalk
GRE Header
IP Tunnel
AppleTalk
Inner IP Header
RFC 1918
IP Payload
RFC 1918
Internet
RFC 1918
IP Tunnel
RFC 1918
Outer IP Header
Inner IP Header
IP Payload

10. Intentionally Blank

11. GRE and IP-IP Tunnel Requirements (1 of 2)
A tunnel interface is required on each tunnel endpoint
GRE and IP-IP tunnels use the gr-x/y/z and ip-x/y/z naming standards, respectively
Tunnel Endpoint A
Internet
Tunnel Endpoint B
Rtr X
gr-0/0/0.0
ip-0/0/0.0
gr-0/0/0.0
ip-0/0/0.0
User A
User B
A single tunnel can be defined on each logical interface.

12. GRE and IP-IP Tunnel Requirements (2 of 2)
An end-to-end communications path is required
Routing Requirements
Tunnel endpoints must have a valid route to the remote endpoint.
All intermediary devices must have a route to the tunnel endpoints.
Tunnel endpoints must have a route that directs traffic into tunnel.
Internet
Tunnel Endpoint A
Tunnel Endpoint B
User A
User B

13. GRE and IP-IP Tunnel Considerations (1 of 3)
By default, GRE and IP-IP tunnels are stateless
Some GRE implementations provide a keepalive mechanism; BFD also accomplishes the same functionality
Internet
Tunnel Endpoint A
Rtr X
Tunnel Endpoint B
User A
User B
Tunnel remains up on side A even though tunnel is down on side B
gr-0/0/0.0 = up
gr-0/0/0.0 = down

14. Intentionally Blank

15. GRE and IP-IP Tunnel Considerations (2 of 3)
Tunnels add additional overhead to packets, which can adversely affect some types of communications
Packets larger than the MTU are fragmented or dropped depending if the DF bit is clear or set
MSS = 1500
Internet
MTU = 1476
MTU = 1476
Tunnel Endpoint A
Tunnel Endpoint B
User A
User B
By default, packets larger than 1476 will either be fragmented or dropped.

16. Intentionally Blank

17. GRE and IP-IP Tunnel Considerations (3 of 3)
The route for the remote tunnel endpoint cannot use the tunnel interface as next hop; if so, the tunnel will bounce
We recommend a very specific route with a low route preference, such as a static route
Destination Prefix
Next Hop
Protocol/ Preference
Static/5
Destination Prefix
Next Hop
Protocol/ Preference
Static/5
Internet
(.2) /30 (.1)
(.1) /30 (.2)
Tunnel Endpoint A
Rtr X
Tunnel Endpoint B
User A
User B
lo0:
lo0:

18. Agenda: IP Tunneling Overview of IP Tunneling GRE and IP-IP Tunnels
Implementing GRE and IP-IP Tunnels

19. Case Study: Objectives and Topology
Use the sample topology and implement a GRE tunnel between R1 and R2 that carries traffic destined to the remote x.0/24 subnet
Internet
(.10) /24 (.1)
(.1) /24 (.10)
(.2) /30 (.1)
(.1) /30 (.2) R1
Rtr X R2
lo0:
lo0:
gr-0/0/0.0
gr-0/0/0.0
Note: The preceding steps used to implement and monitor a GRE tunnel are also applicable to IP-IP tunnels.

20. Case Study: Defining the Tunnel Interface
[edit]
show interfaces gr-0/0/0
unit 0 {
tunnel {
source ;
destination ; }
family inet;
[edit]
show interfaces gr-0/0/0
unit 0 {
tunnel {
source ;
destination ; }
family inet;
We recommend using the loopback addresses as the tunnel source and destination addresses
Family inet is required to process IPv4 packets through the tunnel
Internet
(.10) /24 (.1)
(.1) /24 (.10)
(.2) /30 (.1)
(.1) /30 (.2) R1
Rtr X R2
lo0:
lo0:
gr-0/0/0.0
gr-0/0/0.0

21. Intentionally Blank

22. Case Study: Defining the Required Routes
[edit]
show routing-options static
route /32 next-hop ;
route /24 next-hop gr-0/0/0.0;
[edit]
show routing-options static
route /32 next-hop ;
route /24 next-hop gr-0/0/0.0;
Internet
(.10) /24 (.1)
(.1) /24 (.10)
(.2) /30 (.1)
(.1) /30 (.2) R1
Rtr X R2
lo0:
lo0:
gr-0/0/0.0
gr-0/0/0.0
Note: Remember that all intermediary routers must have a route to the loopback addresses.

23. Case Study: Verifying Operations (1 of 3)
Use the show interfaces interface-name terse command to verify the tunnel interface is up
show interfaces gr-0/0/0 terse
Interface Admin Link Proto Local Remote
gr-0/0/ up up
gr-0/0/ up up inet
show interfaces gr-0/0/0 terse
Interface Admin Link Proto Local Remote
gr-0/0/ up up
gr-0/0/ up up inet
Internet
(.10) /24 (.1)
(.1) /24 (.10)
(.2) /30 (.1)
(.1) /30 (.2) R1
Rtr X R2
lo0:
lo0:
gr-0/0/0.0
gr-0/0/0.0
Note: Remember GRE and IP-IP tunnels are stateless so you should always ensure that both sides are up.

24. Case Study: Verifying Operations (2 of 3)
Use the show route command to ensure that the required routes are installed on both tunnel endpoints
show route
inet.0: 11 destinations, 11 routes (9 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
/ *[Static/5] 01:19:00
> to via ge-0/0/3.0
show route /24
/24 *[Static/5] 01:17:44
> via gr-0/0/0.0

25. Case Study: Verifying Operations (3 of 3)
Send traffic through the tunnel and confirm that interface statistics are increasing on the tunnel interface
ping rapid count 25 source
PING ( ): 56 data bytes
!!!!!!!!!!!!!!!!!!!!!!!!!
ping statistics ---
25 packets transmitted, 25 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.492/3.185/8.064/2.521 ms
show interfaces gr-0/0/0.0 detail | find "traffic statistics"
Traffic statistics:
Input packets:
Output packets: …
Internet
(.10) /24 (.1)
(.1) /24 (.10)
(.2) /30 (.1)
(.1) /30 (.2) R1
Rtr X R2
lo0:
lo0:
gr-0/0/0.0
gr-0/0/0.0

26. Summary In this chapter, we:
Described IP tunneling concepts and applications
Explained the basic operations of GRE and IP-IP tunnels
Configured and monitored GRE and IP-IP tunnels

27. Review Questions What are some common reasons to use IP tunnels?
Name some differences between GRE and IP-IP.
List the key requirements for GRE and IP-IP tunnels.
Why should the route for the remote tunnel endpoint be specific and use a low route preference?

28. Lab 5: IP Tunneling
Configure and monitor a GRE tunnel.