CS558 Sylabus

Making Mobile IP more efficient

Triangular Route taken in the Mobile IP path
- As you saw from the previous discussion, the messages that are sent towards a mobile host are always routed first to the home network and then tunneled to the foreign network where the mobile host is currently residing:
- This kind of triangular is obviously not the most optimal (fastest) way to get to the mobile hosts.
- (Notice that messages from a mobile host to a non-mobile host follows a direct route and does not have this problem).
- To address this "triangular" route inefficiency, the IP mobility solution specifies the use of a bind cache

Bind Cache: a temporal change in a node's routing table

A bind cache is a table containing entries of the following format:
Note that the bind cache contains Host IP address (not network ID as in the routing table).

A bind cache is a temporal routing table separate from the main routing table of a node

When a node need to route a packet, the bind cache is examined first.
If no entry in the cache matches the IP address, then the node use the standard IP routing method to forward the packet.

Additional change

Entries in the bind cache are ALWAYS virtual entries
So, in order to use the bind cache, a host computer that communicates with a mobile host must be upgraded to incorporate IP tunneling capability (which is not normally done).

Routing using a bind cache proceeds as follows:
- The bind cache contains (IP-address, CareOf-IP-address) pairs.
- Host first check if the destination is found in its bind cache
- If the destination is found in the bind cache, the IP message will be tunneled to the CareOf IP address

Setting up entries in the Bind Cache
- The routing entries in the bind cache are managed dynamically by mobile hosts.
- The Internet has defined a management protocol called Internet Control Message Protocol (ICMP)
- The ICMP protocol includes a bind command message used to update the bind cache
- Mobile hosts that arrives on a foreign host can (periodically) send bind messages to their communicating counter parts.
- The bind message will contain:
  1. (IP address of mobile host, IP address of foreign agent) - when the foreign agent solution is used), or
  2. (IP address of mobile host, new IP address at foreign network) - when the DHCP solution is used
  For example: (using the foreign agent solution)
  1. Mobile host sends bind ICMP message containing its IP address and the IP address of the foreign agent (10.0.0.4, 12.0.0.1) to the sender:
  2. When the node receives the bind ICMP message it enters the information in its bind cache
    The result of the bind message is that the sender will now tunnel the messages directly to the mobile host:
Cache entry time out
- After the bind message is processed, the mobile host can move to another network
- Well, this create a problem....
  Consider what happens when the mobile host leaves the current foreign network and attach itself to another foreign network:
  - Messages sent to the mobile hosts will be lost !!!
- Solution ?