1. IP for Mobile hosts

2. Routing for Mobile hosts
Host IP address:- network part : Host part.
Network part tells us which network host is connected to IP routing tables (RTs) only contain network numbers – improve scalability.
What happens if host disconnects from one network and connects to another?
packets mis-delivered if IP address didn’t change.
New IP address is needed
Solution: provide host with new IP address corresponding to new network.
Use DHCP
What happens to ongoing connections?

3. Routing for Mobile hosts
If an application is running while roaming, transition should be transparent to remote host.
Application should continue to run without interruption.
Procedures described to address these issues – mobile IP

4. Routing for Mobile hosts
Important requirements
should work without changes to:
non-mobile hosts
most routers on Internet.
Most routers unchanged, but additional functionality required in some routers.
Home Agent
Foreign Agent

5. Routing for Mobile hosts
Home Agent (HA): located on “home” network of mobile host.
Mobile Host (MH) has a IP address – “home address”.
Network number of “home address” = network # of “home agent”
HA: used by other hosts to send packets to mobile host (MH) – even while MH is ‘roaming’.
Since, HA doesn’t change, it can be used by long-lived applications.
Foreign Agent(FA): located on new network to which MH attaches both HA’s and FA’s periodically announce their presence on the network to which they are attached, using “agent advertisement message”.

6. Routing for Mobile hosts
A MH may solicit an.
Advertisement by HA: allows MH to learn address of HA before leaving home network.
When attaching to a foreign network:
MH hears advertisement from FA.
Registers with FA - provides address of HA, its own IP address.
FA contacts HA and provides a ‘care-of-address’, usually this is IP address of FA.

7. Routing for Mobile hosts
When a host (H1) wants to send packet to MH:
Send to home address of MH.
Packet intercepted by HA.
Packet forwarded to care-of-address (FA)
FA delivers packet to MH.

8. Routing for Mobile hosts
Step 1 is straightforward.
Step 2 is straightforward, except when H1 reaches network A by a different router R1, not HA
To solve this problem use “proxy ARP”
Proxy ARP: similar to ARP, but HA inserts IP address of MH (instead of its own) and its own network address.
Therefore, nodes on the same network associate network address of HA with IP address of MH.

9. Routing for Mobile hosts
Problem: Older ARP information may be cached in some nodes of network.
Solution: Ensure these are ‘updated’ by issuing a “gratuitous ARP” response frame as soon as MH registers with FA.
Step 3 HA sends data to FA using a “tunnel”
Step 4 FA must recognize that IP address is of a registered MH. If it treated packet like an ‘ordinary’ packet, it would send the packet back to HA.
Instead it delivers packet to H.W. address of MH, which was learned during registration process.

10. Route Optimization
Route from sending node to MH can be very sub-optimal, e.g. when both on same network.
Goal: Deliver packets as directly as possible, without passing through HA – “Triangle Routing Problem”
Solution: let sending node (H1) know care-of-address of MH, so it can form its own “tunnel” to FA.
This is an optimization, but is NOT required.

11. Routing for Mobile hosts
When HA sees packet for MH – deduce sender not using optimized route.
Therefore, send “binding update” message to sender in addition to forwarding packet to FA.
Sender may use this “binding update” message to create an entry in its “binding cache” (BC)
BC: contains list of mapping of MH home address and care-of-address.
Later, if H1 wants to send to MH, check in BC, if entry forward – create tunnel to FA.

12. Routing for Mobile hosts
Problem: binding cache may become out of date if MH moves to new network.
If out-of-date cache entry is used, FA will receive packets for a MH not registered on the network.
FA then sends a “binding warning” message back to sender, to tell it not to use this entry.
Works only if FA is not MH itself.
Therefore, cache entries deleted after some time.