C onfiguring Stack Group Bidding Protocol

If more than one home gateway IP address is specified, sessions are load-balanced (round-robin) between the IP addresses. Although this works fine for modems that only use one link, Multilink PPP (MLP) connections are sent to different home gateway routers. For Integrated Services Digital Network (ISDN) MLP connections, half of the packets are lost.

To solve this problem, use Stack Group Bidding Protocol (SGBP). Routers or access servers are configured to belong to groups of peers called stack groups. All members of the stack group are peers; stack groups do not need a permanent lead router.

After a connection is established with one member of a stack group, that member owns the call. If a second call comes in from the same client and a different router answers the call, the router establishes a tunnel and forwards all packets belonging to the call to the router that owns the call. Establishing a tunnel and forwarding calls through it to the router that owns the call is sometimes called projecting the PPP link to the call master.

If a more powerful router is available, it can be configured as an offload router. All group members will establish tunnels and forward calls to this router. In this case, the other stack group members just answer calls and forward traffic to the more powerful offload router.

Peer Configuration

Figure C-1 shows a peer configuration.

Figure C-1: Peer Configuration

1. When the first call comes in to the stack group, Router A answers.

2. In the bidding, Router A wins because it already has the call. Router A becomes the call-master for that session with the remote device.

3. When the remote device that initiated the call needs more bandwidth, it makes a second Multilink PPP call to the group.

4. When the second call comes in, Router E answers it and informs the stack group. Router A wins the bidding because it already is handling the session with that remote device.

5. Router E establishes a tunnel to Router A, and forwards the raw PPP data to Router A.

6. Router A reassembles and resequences the packets.

7. If more calls come in to Router E and they too belong to Router A, the tunnel between A and E enlarges to handle the added traffic. Router E does not establish an additional tunnel to A.

8. If more calls come in and are answered by any other router, that router also establishes a tunnel to A and forwards the raw PPP data.

9. The reassembled data is passed on the corporate network as if it had all come through one physical link.

This section describes how to configure all SGBP members as peers. To configure all members as peers, follow these steps for each home gateway.

Step	Command	Purpose
1	Router# configure terminal Enter configuration commands, one per line. End with Cntl/z.	Enter global configuration mode.
2	Router(config)# sgbp group name	Specify the stack group name. This name must be authenticated locally or with the AAA server.
3	router(config)# sgbp member name	Specify the name of this stack group member.
4	router(config)# vpdn multihop	Enables SGBP for group members.

Table C-1: Configuring an SGBP Member

Step Command Purpose

1

Router# configure terminal
Enter configuration commands, one per line. End with Cntl/z.

Enter global configuration mode.

2

Router(config)# sgbp group name

Specify the stack group name. This name must be authenticated locally or with the AAA server.

3

router(config)# sgbp member name

Specify the name of this stack group member.

4

router(config)# vpdn multihop

Enables SGBP for group members.

Offload Router Configuration

In contrast to the peer configuration, this configuration features an offload router. Access servers that belong to a stack group answer calls, establish tunnels, and forward calls to an offload router that wins the bidding and is the call-master for all calls. The offload router reassembles and resequences all the packets coming in through the stack group.

Figure C-2:
Offload Router Configuration

This section describes how to configure one SGBP member as the offload router and the rest as peers.

Configuring an SGBP Member

To configure an SGBP member as a peer, follow these steps:

Table C-2: Configuring an SGBP Member

Step Command Purpose

1

Router# configure terminal
Enter configuration commands, one per line. End with Ctrl-z.

Enter global configuration mode.

2

Router(config)# sgbp group name

Specify the stack group name. This name must be authenticated locally or with the AAA server.

3

router(config)# sgbp memer name

Specify the name of this stack group member.

4

router(config)# vpdn multihop

Enables SGBP for group members.

Step	Command	Purpose
1	Router# configure terminal Enter configuration commands, one per line. End with Ctrl-z.	Enter global configuration mode.
2	Router(config)# sgbp group name	Specify the stack group name. This name must be authenticated locally or with the AAA server.
3	router(config)# sgbp memer name	Specify the name of this stack group member.
4	router(config)# vpdn multihop	Enables SGBP for group members.

Configuring an SGBP Offload Router

To configure an SGBP member as an offload router, follow these steps:

Step	Command	Purpose
1	Router# configure terminal Enter configuration commands, one per line. End with Ctrl-z.	Enter global configuration mode.
2	Router(config)# sgbp group name	Specify the stack group name. This name must be authenticated locally or with the AAA server.
3	router(config)# sgbp member name	Specify the name of this stack group member.
4	router(config)# sgbp seed-bid offload	Configure this router to act as the offload router. All group members will establish tunnels and forward calls to this router.

Table C-3: Configuring an SGBP Offload Router

Step Command Purpose

1

Router# configure terminal
Enter configuration commands, one per line. End with Ctrl-z.

Enter global configuration mode.

2

Router(config)# sgbp group name

Specify the stack group name. This name must be authenticated locally or with the AAA server.

3

router(config)# sgbp member name

Specify the name of this stack group member.

4

router(config)# sgbp seed-bid offload

Configure this router to act as the offload router. All group members will establish tunnels and forward calls to this router.

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