Cisco Cisco IOS Software Release 12.4(9)T

Upon successful registration, the home agent will maintain multiple care-of addresses, mobility 
bindings, tunnels, and routes to the same mobile router. Multiple bindings are not the same as 
simultaneous bindings. With simultaneous bindings, the traffic to a mobile node is replicated on all 
tunnels. With multiple bindings, the traffic is not replicated on all tunnels but rather load-balanced across 
them. 

When there are multiple paths between the mobile router and the home agent, the traffic from the mobile 
networks that goes toward the home agent can be load-balanced by one of the following methods:

Per-packet load balancing

Per-destination load balancing

For both of these methods, traffic is load-balanced in a round-robin fashion among multiple paths. 

Both of these methods support equal and unequal load balancing. Equal load balancing of packets (or 
sessions) among the multiple paths between the mobile router and the home agent can cause congestion 
because of the interfaces with lower bandwidth. To accommodate this situation, the Mobile Router 
Multipath Support feature uses the roaming interface bandwidth of the associated tunnel as the default 
metric. For example, if a mobile router registers to a home agent through two interfaces, one with a 
bandwidth of 1000 and the other with a bandwidth of 500, two packets will go through the first interface 
and the third packet will go through the second interface.

Per-packet load balancing allows the router to send data packets over successive paths without regard to 
individual destination hosts or user sessions. Path utilization is good, but packets destined for a given 
destination host might take different paths and might arrive out of order. This behavior has the 
disadvantage of causing packets in the same session to follow different routes through the network, 
causing the packet reordering and nonpredictive latency for that session.

Per-destination load balancing is the default behavior for this feature and addresses the disadvantages of 
per-packet load balancing. Per-destination load balancing allows the router to use multiple, equal-cost 
paths to achieve load sharing. In per-destination load sharing, each tunnel is considered based on the 
destination or session. If the packet is destined for the same destination as taken previously, the same 
path is chosen. Packets in the same session stay in the same order and follow the same route across the 
network, which helps maintain the latency for each packet.

Because multiple access technologies can be deployed in mobile networks, the Mobile Router Multipath 
Support feature offers the ability to leverage all available links when Mobile IP is used. This multiple 
path support offers a good investment protection for existing legacy wireless connections or any newly 
purchased or deployed wireless technologies.