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Configurations required for load balancing for AR28-11 Adsl -ATM module without Multilink PPP.

Publication Date:  2012-07-27 Views:  57 Downloads:  13
Issue Description
The customer  sent the following email below:
We have a AR28-11 with a RT-2ADSL MIM card. Both ATM circuits (ATM1/0 and ATM1/1) are connected to ADSL connections - both are UP. We need to load share between these two circuits. What is the best way to do this? We were planning to do this using OER on Cisco.
Alarm Information
      Sample Configuration below:
<AR28_CF>display version
  [SLOT 1] 2ADSL    (Hardware)2.0, (Driver)2.0, (Cpld)2.0
<AR28_CF>display current-configuration
 sysname AR28_CF
interface Virtual-Template0
 ppp chap user user1@domain
 ppp chap password simple lkjhgfds
 ip address ppp-negotiate
interface Virtual-Template1
 ppp chap user user2@domain
 ppp chap password simple kjhgfds
 ip address ppp-negotiate
interface Aux0
 async mode flow
 link-protocol ppp
interface Ethernet0/0
 ip address
interface Ethernet0/1
 ip address
interface Serial0/0
 clock DTECLK1
 link-protocol ppp
interface Atm1/0
 adsl standard gdmt
 pvc 0/38
  map ppp Virtual-Template0
interface Atm1/1
 adsl standard gdmt
 pvc 0/38
  map ppp Virtual-Template1
interface NULL0
 ip route-static Virtual-Template 1 preference 60
user-interface con 0
user-interface aux 0
user-interface vty 0 4
 authentication-mode local
 user privilege level 3
 set authentication password cipher a.BCFC&Y;<KQBC:RRU/-W1!!
Handling Process
A simple way of achieving load balancing/load sharing is based on the principle of equal cost routes using the routing protocol employed for the network.
Section 1.22 in the Operation Manual Routing Protocol for VRP 3.3 and VRP 3.4 explain how Load- balancing can be achieved either by per flow, per packet or bandwidth based.
Section 1.3 in the VRP 3.4 Operation Manual 06 Routing Protocol has an example on how to configure load-balancing based on unequal bandwidth.   
Section 4.4.2 in the VRP 3.3 Operation Manual Network Protocol has details on how to enable/disable fast forwarding on an interface.
In summary, based on static routing , as an example the command required to add to the case (query) sample configuration is : ip route-static Virtual-Template 2 preference 60  which enables a per-flow load-balancing with fast forwarding enabled.
If you prefer to use a per-packet load-balancing, you need to disable fast forwarding on the ATM interfaces using the command : undo ip fast-forwarding (options to apply on incoming or outgoing on the interface, might be absent in VRP 3.3).
For bandwidth-based load-sharing, please refer to the  VRP 3.4 Operation Manual 06 Routing Protocol for the commands.
Root Cause
1. we can only use equal-cost routes to achieve load balancing.
2. we can enable fast-forwarding ( by default) to make sure that traffic is forwarded per flow, which will avoid the issue where the return traffic follows a different path (or circuit) from which it was sent.
Load sharing is supported by four routing protocols: static routing, OSPF, BGP, and IS-IS. The following load sharing implementations are available:
Per-flow load sharing. When fast forwarding (the default) is enabled, the router can implement only per-flow load sharing. Suppose two equal-cost routes are available on the router. When one data flow arrives, the router forwards it on one route. When two data flows arrive, the router forwards each on one route. Likewise, the fast forwarding-enabled subinterfaces implement per-flow load sharing.
Per-packet load sharing, implemented when fast forwarding is disabled. The router then distributes the arrived packets equally on the participating routes.
Bandwidth-based unbalanced load sharing. When fast forwarding is disabled, the router implements per-packet load sharing to distribute load depending on the physical bandwidth of interface. You can however allocate load bandwidth to each interface. The router then distributes load on the participating interfaces depending on the ratio of their load bandwidths.