Mobile IP is part of both IPv4 and IPv6 standards. Mobile IP allows a host device to be identified by a single IP address even though the device may move its physical point of attachment from one network to another. Regardless of movement between different networks, connectivity at the different points is achieved seamlessly without user intervention. Roaming from a wired network to a wireless or wide-area network is also done with ease. Mobile IP provides ubiquitous connectivity for users, whether they are within their enterprise networks or away from home.
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Mobile IPv4 provides an IPv4 node with the ability to retain the same IPv4 address and maintain uninterrupted network and application connectivity while traveling across networks. In Mobile IPv6, the IPv6 address space enables Mobile IP deployment in any kind of large environment. No foreign agent is needed to use Mobile IPv6.
System infrastructures do not need an upgrade to accept Mobile IPv6 nodes. IPv6 autoconfiguration simplifies mobile node (MN) Care of Address (CoA) assignment.
Mobile IPv6 benefits from the IPv6 protocol itself; for example, Mobile IPv6 uses IPv6 option headers (routing, destination, and mobility) and benefits from the use of neighbor discovery.
Mobile IPv6 provides optimized routing, which helps avoid triangular routing. Mobile IPv6 nodes work transparently even with nodes that do not support mobility (although these nodes do not have route optimization).
Mobile IPv6 is fully backward-compatible with existing IPv6 specifications. Therefore, any existing host that does not understand the new mobile messages will send an error message, and communications with the mobile node will be able to continue, albeit without the direct routing optimization.
How Mobile IPv6 Works
To implement Mobile IPv6, you need a home agent on the home subnet on which the mobile node’s home address resides. The IPv6 home address (HA) is assigned to the mobile node. The mobile node obtains a new IPv6 address (the CoA) on networks to which it connects. The home agent accepts BUs from the mobile node informing the agent of the mobile node’s location. The home agent then acts as proxy for the mobile node, intercepting traffic to the mobile node’s home address and tunneling it to the mobile node.
The mobile node informs a home agent on its original home network about its new address, and the correspondent node communicates with the mobile node about the CoA. Because of the use of ingress filtering, the mobile node reverses tunnel return traffic to the home agent, so that the mobile node source address (that is, its home address) will always be topographically correct.
Mobile IPv6 is the ability of a mobile node to bypass the home agent when sending IP packets to a correspondent node. Optional extensions make direct routing possible in Mobile IPv6, though the extensions might not be implemented in all deployments of Mobile IPv6.
Direct routing is built into Mobile IPv6, and the direct routing function uses the IPv6 routing header and the IPv6 destination options header. The routing header is used for sending packets to the mobile node using its current CoA, and the new home address destination option is used to include the mobile node’s home address, because the current CoA is the source address of the packet.
Mobile IPv6 Home Agent
The home agent is one of three key components in Mobile IPv6. The home agent works with the correspondent node and mobile node to enable Mobile IPv6 functionality:
Home agent--The home agent maintains an association between the mobile mode’s home IPv4 or IPv6 address and its CoA (loaned address) on the foreign network.
Correspondent node--The correspondent node is the destination IPv4 or IPv6 host in session with a mobile node.
Mobile node--An IPv4 or IPv6 host that maintains network connectivity using its home IPv4 or IPv6 address, regardless of the link (or network) to which it is connected.
The following sections describe Mobile IPv6 home agent functionality:
A separate binding cache is maintained by each IPv6 node for each of its IPv6 addresses. When the router sends a packet, it searches the binding cache for an IPv6 address before it searches the neighbor discovery conceptual destination cache.
The binding cache for any one of a node’s IPv6 addresses may contain one entry for each mobile node home address. The contents of all of a node’s binding cache entries are cleared when it reboots.
Binding cache entries are marked either as home registration or correspondent registration entries. A home registration entry is deleted when its binding lifetime expires; other entries may be replaced at any time through a local cache replacement policy.
Binding Update List in Mobile IPv6 Home Agent
A binding update (BU) list is maintained by each mobile node. The BU list records information for each BU sent by this mobile node whose lifetime has not yet expired. The BU list includes all BUs sent by the mobile node--those bindings sent to correspondent nodes, and those bindings sent to the mobile node’s home agent.
The mobility extension header has a new routing header type and a new destination option, and it is used during the BU process. This header is used by mobile nodes, correspondent nodes, and home agents in all messaging related to the creation and management of bindings.
Home Agents List
A home agents list is maintained by each home agent and each mobile node. The home agents list records information about each home agent from which this node has recently received a router advertisement in which the home agent (H) bit is set.
Each home agent maintains a separate home agents list for each link on which it is serving as a home agent. This list is used by a home agent in the dynamic home agent address discovery mechanism. Each roaming mobile node also maintains a home agents list that enables it to notify a home agent on its previous link when it moves to a new link.
IPv6 Neighbor Discovery with Mobile IPv6
The IPv6 neighbor discovery feature has the following modifications to allow the feature to work with Mobile IPv6:
Modified router advertisement message format--has a single flag bit that indicates home agent service
Modified prefix information option format--allows a router to advertise its global address
New advertisement interval option format
New home agent information option format
Changes to sending router advertisements
Provide timely movement detection for mobile nodes
Displays information about BUs received and BAs sent.
Customizing Mobile IPv6 on the Interface
Perform this task to customize interface configuration parameters for your router configuration. You can set these interface configuration parameters before you start Mobile IPv6 or while Mobile IPv6 is in operation. You can customize any of these parameters, as desired.
The following example shows how to configure and enable Mobile IPv6 on a specified interface:
Example: Viewing IPv6 Mobile Information on an Interface
Device(config-if)# ipv6 nd ra-interval 100 60
Subsequent use of the show ipv6 interface then displays the interval as follows:
Router(config)# show ipv6 interface ethernet 1/0
Ethernet1/0 is administratively down, line protocol is down
IPv6 is enabled, link-local address is FE80::A8BB:CCFF:FE00:5A01 [TEN]
No Virtual link-local address(es):
No global unicast address is configured
Joined group address(es):
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds
ND advertised reachable time is 0 milliseconds
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 60 to 100 seconds
ND router advertisements live for 1800 seconds
ND advertised default router preference is Medium
Hosts use stateless autoconfig for addresses.
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Table 1 Feature Information for Mobile IPv6 Home Agent
Mobile IPv6 Home Agent
The Mobile IPv6 feature uses the IPv6 address space to enable Mobile IP deployment in any kind of large environment. No foreign agent is needed to use Mobile IPv6.
The following commands were introduced or modified:
ipv6 mobile home-agent,
ipv6 nd advertisement-interval,
ipv6 nd prefix,
ipv6 nd ra interval,
show ipv6 mobile globals,
show ipv6 mobile home-agent.