Operation Manual - Link Layer Protocol
H3C SecPath F1800-A Firewall
Chapter 2 PPP Configuration
4-11
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The requester will look for the user password based on the authenticator’s
hostname in the received packet and its own user list. If it finds the user in the
user list with the same name as the authenticator’s hostname, the requester
encrypts this random packet with the packet ID, user’s key (password) by using
the MD5 algorithm. Then it sends the generated encrypted text and its own
hostname to the authenticator.
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The authenticator encrypts the original random packet with its locally saved
password of requestor by using the MD5 algorithm. Then it compares the
encryption result with the response from the requester. If both are identical, the
“Acknowledge” response is returned; if both are different, the “Not Acknowledge”
response is returned.
III. PPP Operation Process
1)
When the physical layer is unavailable, the PPP link is in the “dead” phase. The
link must start with and end in this phase. When the physical layer becomes
available, the PPP link enters the “establish” phase.
2) LCP negotiation should be carried out on the PPP link in the “establish” phase,
including operating mode (SP or MP), authentication mode and MTU. After LCP
negotiation is successful, the status of LCP is “opened”, which indicates that the
lower layer link has been established.
3)
If the authentication is not configured, it enters network negotiation phase. At this
moment, the status of LCP is still “opened”, while the status of NCP changes
from “initial” to “request-sent” and enters 5); If the authentication (the remote
verifies the local or the local verifies the remote) is configured, it enters the
“authenticate” phase and begins CHAP or PAP authentication and enters 4).
4)
If the authentication fails, it enters the “terminate” phase, the link is removed and
LCP turns to Down. After successful authentication, the network negotiation
phase (NCP) begins. At this time, the status of LCP is still “opened”, while the
status of NCP is changed from “initial” to “request-sent”.
5) NCP negotiation supports the negotiations of IPCP and IPXCP, of which IPCP
negotiation mainly includes the IP addresses of two parties. Network layer
protocols are selected and configured through the NCP negotiation. The related
network layer protocol must be negotiated successfully before this network layer
protocol sends messages through this PPP link.
6)
PPP link will remain in communication status until a specific LCP or NCP frame
closes this link or some external events take place (for example, the intervention
of users).