Using IP Tunneling

This document describes how to use the IP tunneling. It includes the following sections:

Tunneling and Multicast Packets

Bridging IP Tunnel

Bridging IP tunnel is another feature of the ASRT bridging software. With the bridging tunnel feature enabled, the software encapsulates packets in TCP/IP packets. To the router, the packet looks like a TCP/IP packet. Once a frame is encapsulated in an IP envelope, the IP forwarder is responsible for selecting the appropriate network interface based on the destination IP address. This packet can be routed dynamically through large internetworks without degradation or network size restrictions.

The IP tunnel appears to the bridge as one of the bridge ports using IP as a means of input/output device. On the tunnel bridge port you can configure STB, SRB or SRT bridge behavior.

In SRB configuration, IP tunnel helps overcome the usual 7-hop distance limit encountered in source routing configurations. It also lets you connect source- routing end stations across non-source-routing media, such as Ethernet networks.

The bridging tunnel also reduces the large amounts of overhead that source routing causes in wide area networks (WANs)

Finally, it reduces source-routing's sensitivity to WAN faults and failures (if a path fails, all systems must restart their transmissions)

End stations see this path or tunnel, as a single hop, regardless of the complexity of the internetwork. Figure 1 shows an example of an IP internetwork using the tunnel feature in its configuration.

Figure 1 End Stations See Routing Across Complex IP Internet as One Hop

The bridges participating in tunneling treat the IP internet as one of the bridge segments. When the packet reaches the destination interface, the TCP/IP headers are automatically removed and the inner packet proceeds as a standard source-routing packet.

Encapsulation and OSPF

A major benefit of the encapsulation feature is the addition of the OSPF dynamic routing protocol to the routing process. OSPF offers the following benefits when used with encapsulation:

Least-cost Routing. OSPF accesses the fastest path (tunnel) with the fewest delays, allowing network administrators to distribute traffic over the least expensive route.
Dynamic Routing. OSPF looks for the least-cost path, detects failures, and reroutes traffic with low overhead.

With OSPF, tunnels automatically manage paths inside the internetwork. If a line or bridge fails along the path then the tunnel bridge automatically reroutes traffic along a new path. If a path is restored, the tunnel automatically updates to the best path. This rerouting is completely transparent to the end stations.

Tunneling and Multicast Packets

For tunnel configurations where multicast packets are involved, the source address of the multicast packets must lie on a network segment that is capable of the Internet Group Management Protocol (IGMP).

IGMP is not defined on X.25 or Frame Relay configurations, so when running multicast applications on the router (e.g., the MOSPF tunnel) take care if one of the following conditions hold:

The source is one of the LAN segment addresses.
The source is the internal IP address.

You can ensure the first condition by using the IP set router-id configuration command. You can ensure the second condition by using the IP set internal-ip-address configuration command.

In all cases, the second option is preferable. Use the first only if some of the routers in the network do not like host addresses (this might happen in mixed vendor networks).

IP Tunnel Commands

Enter commands for specifically defined tunnels at the Tunnel(#)config> prompt. To get this prompt, enter tunnel at the Bridge Config> or Bridge> prompt. Table 1 lists the tunnel commands.

Not all parameters apply to all router platforms. Press Space twice after you type a command to display the available parameters for each command for your router. Enter help for information about using the command line interface.

[C] means the command is available at the Tunnel(#)config> prompt.

[M] means the command is available at the Tunnel(#)> prompt.

Table 1 Tunnel Commands

Command Function

Add [C] Adds the IP address of destination bridges participating in an IP unicast or multicast addressing configuration for bridging over IP.

Delete [C] Deletes the IP address of a destination bridge participating in an IP unicast or multicast addressing configuration for bridging over IP.

Exit [C] [M] Returns to the previous prompt.

Join [C] Establishes the router as a member of one or more multicast groups.

Leave [C] Removes the router as a member of multicast groups.

List [C] [M] At the configuration prompt, displays the IP addresses of endstations participating in an IP unicast or multicast addressing configuration for bridging over IP. Also displays the size (in bytes) of bridging packets being routed through an IP tunnel and whether or not multicast addressing is enabled or disabled.
At the monitoring prompt, lists tunnel bridges and tunnel configurations.

Set [M] Sets a base multicast address for the router.

Table 1 Tunnel Commands
Command	Function
Add [C]	Adds the IP address of destination bridges participating in an IP unicast or multicast addressing configuration for bridging over IP.
Delete [C]	Deletes the IP address of a destination bridge participating in an IP unicast or multicast addressing configuration for bridging over IP.
Exit [C] [M]	Returns to the previous prompt.
Join [C]	Establishes the router as a member of one or more multicast groups.
Leave [C]	Removes the router as a member of multicast groups.
List [C] [M]	At the configuration prompt, displays the IP addresses of endstations participating in an IP unicast or multicast addressing configuration for bridging over IP. Also displays the size (in bytes) of bridging packets being routed through an IP tunnel and whether or not multicast addressing is enabled or disabled. At the monitoring prompt, lists tunnel bridges and tunnel configurations.
Set [M]	Sets a base multicast address for the router.

Add [C]

Adds the IP address of endstations participating in a unicast or multicast IP addressing configuration.

For IP unicast addressing, the tunneling configuration requires you to supply IP addresses of destination bridges. The router software uses this record to convert the segment number in the RIF (Routing Information Field) in a source-routed frame to the corresponding IP address of the destination bridge. For transparent bridging frames, the record identifies the other end point of the tunnel.

For IP multicast addressing, the tunneling configuration requires only the IP multicast address reserved for tunneling. Encapsulation uses three groups of IP multicast addresses. The first group is for sending ARE frames, the second group for sending STE frames, and the third group for SRF.

Note: The bridging software transparently differentiates between unicast and multicast addresses.

Syntax: add address IP-address

Example: add address 128.185.144.37

Delete [C]

Deletes the IP address of bridges participating in a unicast or multicast IP addressing configuration.

Syntax: delete address IP-address

Example: delete address 128.185.144.37

Exit [C] [M]

Returns to the previous prompt.

Syntax: exit

Example: exit

Join [C]

Establishes the router as a member of one or more multicast groups. A tunnel group can be a peer, client, or server, and is defined by an integer tag. A bridge can belong to only one group type for each tag. A bridge cannot belong, for example, to both peer group 1 and server group 1.

Syntax: join

server-group
client-group
peer-group

server-group group-number

Makes the router a member of the server group with the group number.

Example: join server-group 7

client-group group-number

Makes the router a member of the client group with the group number.

Example: join client-group 3

peer-group group-number

Makes the router a member of the peer group with the group number.

Example: join peer-group 5

Leave [C]

Removes the router from membership in multicast groups.

Syntax: leave

server-group
client-group
peer-group

server-group group-number

Removes the router from membership in the server group with the given group number.

Example: leave server-group 7

client-group group-number

Removes the router from membership in the client group with the given group number.

Example: leave client-group 3

peer-group group-number

Removes the router from membership in the peer group with the given group number.

Example: leave peer-group 5

List [C] [M]

Displays the IP addresses of bridges participating in an IP unicast or multicast addressing configuration for tunneling over IP. Displays the current size of IP packets being sent through the tunnels and whether or not IP is enabled or disabled.

List [C]

Displays the IP addresses of bridges participating in an IP unicast or multicast addressing configuration for tunneling over IP.

Syntax: list

address
all

address

Lists the IP addresses of bridges participating in an IP unicast or multicast addressing configuration for tunneling over IP.

Example: list address

IP Tunnel Addresses
128.185.179.51      128.185.170.51      128.185.142.39 128.185.143.39       224.0.0.5

all

Lists all unicast IP addresses, configured multicast addresses, and the tunnel packet size.

Example: list all

IP Tunnel Addresses
 128.185.179.51      128.185.170.51      128.185.142.39
 128.185.143.39      224.0.0.5     

Frame size for the tunnel 2120
Frame size for the tunnel 2120

List [M]

Displays the IP addresses of bridges participating in an IP unicast or multicast addressing configuration for tunneling over IP.

Syntax: list

tunnel

tunnel bridges or config

Use the bridges option to list the source routing segment and address of bridges. Use the config option to list the tunnel configuration.

Example: list tunnel bridges

SR segment IP address

Set [M]

Sets the base multicast IP address of the router for multicast tunneling.

Syntax: set

base-multicast-address

Example: set base-multicast-address 224.10.0.0

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