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Configuring Mobile IP
How Mobile IP Works
IPC-163
Cisco IOS IP Configuration Guide
Figure 28 Mobile IP Typical Packet Forwarding
Mobile IP Security
Mobile IP provides the following guidelines on security between its components:
• Communication between MN and HA must be authenticated.
• Communication between MN and FA can optionally be authenticated.
• Communication between FA and HA can optionally be authenticated.
Also, communication between an active HA and a standby HA, as implemented when using the HA
redundancy feature, must be authenticated. For more information on this feature, see the “Home Agent
Redundancy” section later in this chapter.
MN-HA
In particular, the Mobile IP registration process is vulnerable to security attacks, because it informs the
HA where to tunnel packets to a traveling MN. An illegitimate node could send a bogus registration
request to an HA and cause all packets to be tunneled to the illegitimate node instead of the MN. This
type of attack, called a denial-of-service attack, prevents the MN from receiving and sending any
packets. To prevent denial-of-service attacks, Mobile IP requires that all registration messages between
an MN and an HA be authenticated.
Cisco IOS software supports the Mobile-Home Authentication Extension (MHAE). All registration
messages between an MN and an HA include a mandatory authentication extension.
Message Digest 5 (MD5) is an algorithm that takes the registration message and a key to compute the
smaller chunk of data, called a message digest, plus a secret key. The MN and HA both have a copy of
the key, called a symmetric key, and authenticate each other by comparing the results of the computation.
The time stamp is an identifier in the message that ensures the origination of the registration request and
the time it was sent, thereby preventing replay attacks. A replay attack occurs when an individual records
an authentic message that was previously transmitted and replays it at a later time. The time stamp is
also protected by MD5.
Mobile node
visiting foreign
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Mobile node
at home
Internet
Foreign
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Home
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Foreign
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Home
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Correspondent
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