Information Technology Reference
In-Depth Information
Table17-12 PPP NCP Negotiation Details
Time Stamp
Description
21:35:04.190
Outgoing configuration request (O CONFREQ). The NAS sends an
outgoing PPP configuration request packet containing its IP address
to the peer.
21:35:04.282
Incoming CONFREQ. The peer requests to do VJ header
compression and needs an IP address for itself, as well as addresses
of the primary and secondary DNS servers.
21:35:04.306
Outbound Config-Reject (CONFREJ). VJ header compression is
rejected.
21:35:04.314
to
21:35:04.330
The peer sends a request to do Compression Control Protocol; the
entire protocol is rejected by the NAS by means of a PROTREJ
message. The peer should not (and does not) attempt to retry CCP.
21:35:04.334
The peer acknowledges the IP address of the NAS with a CONFACK.
21:35:07.274
Incoming CONFREQ. The peer no longer requests to do VJ header
compression, but it still needs an IP address for itself, as well as
addresses of the primary and secondary DNS servers.
21:35:07.294
The NAS sends a CONFNAK containing the address that it wants the
peer to use, along with addresses of the primary and secondary DNS
servers.
21:35:07.426
The peer sends the addresses back to the NAS—in effect, an attempt
to confirm that the addresses were properly received.
21:35:07.458
The NAS acknowledges the addresses with a CONFACK.
21:35:07.478
Each side of the connection has issued a CONFACK, so negotiation
is finished. The command
show interfaces Async4
on the NAS will
show “IPCP: Open.”
21:35:07.490
A host route to the remote peer is installed in the NAS's routing table.
It should be noted that it is possible for the peers to simultaneously negotiate more than one Layer 3
protocol. It is not uncommon, for instance, to see IP and IPX being negotiated. It is also possible for one
protocol to successfully negotiate while the other fails to do so.
Any problems that occur during NCP negotiation can typically be traced to the configurations of the
negotiating peers. If PPP negotiation fails during the NCP phase, take the steps outlined in Table 17-13.
Table17-13 Troubleshooting NCP
Task
Steps
Verify
interface
protocol
configuration.
Examine the output of the privileged exec command
show
running-config
. Verify that the interface is configured to support the
protocol that you want to run over the connection.
Verify
interface
address.
Confirm that the interface in question has an address configured. If
your are using
ip unnumbered [
interface-name
]
or
ipx ppp-client
loopback [
number
]
, ensure that the referenced interface is
configured with an address.
