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Configuring DLSw Peer Preference and Load Balancing (Optional)

For a DLSw J-series router, when more than one remote DLSw peer provides alternate paths to a remote destination on a WAN, you can specify preferences by assigning costs among the available routers (peers) or enable load balancing for lowest equal-cost alternatives. The DLSw router maintains a reachablity cache of paired MAC address and IP address entries to determine whether an SNA host can be reached by means of any of the peers the router has information about.

Consider a WAN in which the DLSw Services Router R1 has a peer relationship with more than one peer routers as shown in Figure 13. The peer routers R2 and R3 are manufactured by vendors other than Juniper Networks.

Figure 13: DLSw Peer Preference and Load-Balancing Network Topology

Image g017254.gif

As shown in Figure 13, the far-end routers R2 and R3 provide alternate paths to Host H2 from Router R1. Router R2 has an IP address of 192.168.17.2, and Router R3 has an IP address of 192.168.18.2. A DLSw circuit between the local host H1 and the remote host H2 can be established through either R2 or R3.

By default, a Services Router has no preference for a next-hop router among its DLSw peers. Router R1 checks its reachability cache for entries. If none exist, R1 sends a canureach message to peers R2 and R3 and selects the first responding router as the next hop to the destination host H2.

You can specify preferences among peers R2 and R3 by assigning a different cost to each. For example, if you assign a cost of 50 to R2 and a cost of 60 to R3, Router R2 is the preferred next-hop peer. Then, Router R1 waits for a specified period of time to get a response from R2. If both R2 and R3 respond, the circuit is routed through R2. If R2 does not respond in the specified time, and R3 responds, then the DLSw router R1 accepts R3's response and the circuit is routed through R3.

To ensure load balancing among peers, you must assign the least cost for the peer routers, and additionally assign them different circuit weights. Assigning circuit weights ensures that the number of circuits going through each peer is balanced according to the circuit weight configured on each peer. For example, if R2 and R3 both have a cost of 50, but R3 can handle more DLSw traffic, then you can assign a circuit weight of 1 to R2 and a circuit weight of 2 to R3 to ensure that twice as much DLSw traffic is routed to Router R3.

To configure DLSw load balancing:

  1. Navigate to the top of the configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 65.
  3. If you are finished configuring the router, commit the configuration.
  4. To verify the DLSw configuration, see Verifying DLSw Configuration.

Table 65: Configuring DLSw Peer Preference and Load Balancing on DLSw and Peer Routers

Task

J-Web Configuration Editor

CLI Configuration Editor

Navigate to the Dlsw level in the configuration hierarchy.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Protocols, click Configure or Edit.
  3. Next to Dlsw, make sure the check box is selected, and click Configure or Edit.

Note: You can also navigate through the navigation hierarchy in the left pane.

From the [edit] hierarchy level, enter

edit protocols dlsw

Configure the load-balancing settings for the first remote DLSw peer:

  • IP address—for example, 192.168.17.2
  • Circuit weight of between 1 and 127—for example, 1
  • Circuit cost of between 0 and 127—for example, 50
  • Keepalive interval of between 0 and 4294967295 seconds—for example, 20. The default interval is 10 seconds. Setting an interval of 10 seconds ensures that the circuit is always available.

Then configure settings for the second remote peer, using an IP address of 192.168.18.2and a circuit weight of 2.
  1. Next to Remote peer, click Configure.
  2. Click Add new entry.
  3. In the Peer ip box, type 192.168.17.2.
  4. In the Circuit weight box, type 1.
  5. In the Cost box, type 50.
  6. In the Keepalive interval box, type 20.
  7. Click OK until you return to the DLSw page.
  8. Repeat Steps 1 through 7 for the second remote peer.
  1. Enter

    set remote-peer 192.168.17.2

  2. Enter

    set load-balance circuit-weight 1

  3. Enter

    set cost 50

  4. Enter

    set keepalive-interval 20

  5. Repeat Steps 1 through 4 for the second remote peer.

Configure the interval during which the DLSw router waits for a response to its explorer requests from the peer routers. The interval ranges from 5 through 60 seconds, and the default value is 10 seconds.

Configure the interval for retaining entries in the reachability cache. The interval ranges from 100 through 3600 seconds, and the default value is 900 seconds.
  1. In the Explorer wait time box, type 5.
  2. In the Reachability cache timeout box, type 300.
  3. Click OK to return to the Configuration Protocols page.
  1. From the edit protocols dlsw hierarchy level, enter

    set explorer-wait-time 5

  2. Enter

    set reachability-cache-timeout 300

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