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Optional Configuration Tasks

You can perform the following optional PPP configuration tasks:

Add a text description or alias to a PPP interface.
Configure the IPCP netmask option (option 0x90).
Specify the keepalive timeout value.
Disable magic numbers.
Control validation of the LCP peer magic number when the peer has not negotiated an LCP magic number.
Configure the maximum number of LCP, IPCP, or IPv6CP renegotiation attempts that the router accepts before terminating a PPP session.
Specify the maximum receive units.
Configure passive mode.
Configure name server addressing.
Stop or restart a PPP session.
Configure PPP authentication.

ppp description

Use to assign a text description or alias to a static PPP interface.
Examplehost1(config-if)#ppp description pah8999
Use the no version to remove the description.
See ppp description.

ppp ipcp netmask

Use to specify the IPCP netmask option (option 0x90) for each PPP interface. By default, the IPCP netmask option is disabled on the interface.
The IPCP netmask option is a nonstandard option that enables a peer to request the netmask associated with the assigned IP address.
The netmask can be specified via RADIUS attribute 9, Framed-Ip-Netmask. If the netmask is 255.255.255.255, the option is not negotiated. See the radius ignore framed-ip-netmask command.
You can enable the IPCP netmask option either in a profile or on a static interface.
Examplehost1(config-subif)#ppp ipcp netmask
Use the no version to disable the IPCP netmask option on the interface.
See ppp ipcp netmask.

ppp keepalive

Use to specify the keepalive timeout value.
There are two keepalive modes of operation: high-density mode and low-density mode.
- High-density keepalive mode is automatically selected if PPP is layered over ATM, L2TP, or PPPoE.
- Low-density keepalive mode is selected if PPP is layered over HDLC. Keepalive mode selection is made per interface.
High-density mode—This mode is also known as smart keepalive. When the keepalive timer expires, the interface first verifies whether any frames were received from the peer in the prior keepalive timeout interval. If so, the interface does not send an LCP echo request (keepalive). Keepalive packets are sent only if the peer is silent (that is, no traffic was received from the peer during the previous keepalive timeout interval). If both sides are configured with keepalive, receipt of an LCP echo request by one end suppresses the transmission of an LCP echo request by that end. Smart keepalive is disabled when the keepalive timeout value is at least 60 seconds, even when in high-density mode. Smart keepalive is always disabled when in low-density mode. This mode suppresses transmission of unnecessary LCP echo requests.
For high-density keepalive mode, the range is 30–64800 seconds. The default value is 30 seconds.
Low-density mode—When the keepalive timer expires, the interface always sends an LCP echo request, regardless of whether the peer is silent.
For low-density keepalive mode, the range is 1–64800 seconds for POS uplink interfaces, and 10–64800 seconds for all other HDLC interfaces. The default value for all interfaces is 30 seconds.
If the keepalive interval is 30 seconds, a failed link is detected between 90 and 120 seconds after failure.
Use ppp keepalive without a value to restore the default, 30 seconds.
Examplehost1(config-if)#ppp keepalive 50
Use the no version to disable keepalive.
See ppp keepalive.

ppp magic-number disable

Use to disable negotiation of the local magic number.
Issuing this command prevents the router from detecting loopback configurations.
Examplehost1(config-if)#ppp magic-number disable
Use the no version to restore negotiation of the local magic number.
See ppp magic-number disable.

ppp magic-number ignore-mismatch

Use to cause the router to ignore a mismatch of the LCP peer magic number and retain the PPP connection when the peer has not negotiated an LCP magic number.
For more information about using this command, see Validation of LCP Peer Magic Number.
Examplehost1(config-if)#ppp magic-number ignore-mismatch
Use the no version to restore the default behavior, in which the router terminates the PPP connection if it detects an LCP peer magic number mismatch.
See ppp magic-number ignore-mismatch.

ppp max-negotiations

Use to configure the maximum number of LCP, IPCP, or IPv6CP renegotiation attempts, in the range 1–65535, that the router accepts before terminating a PPP session.
Configuring the maximum number of renegotiation attempts helps avoid massive renegotiation loops that can occur between the router and a noncompliant PPP client. Such renegotiation loops can cause excessive CPU utilization and can prevent the PPP client from coming up properly.
When a PPP client exceeds the configured maximum number of renegotation attempts, the router sends a termination request to end the PPP session. When the PPP session is terminated and LCP goes into a stopped (closed) state, static PPP or MLPPP interfaces go into passive mode and wait for the other side of the connection to start the LCP negotiation process.
If you do not specify the optional lcp, ipcp, or ipv6cp keyword, the ppp max-negotiations command sets the maximum number of renegotiation attempts for each of LCP, IPCP, and IPv6CP to the value you specify, or to the default value (30) if you omit the optional value for maximum renegotiation attempts.
When both IPv4 interface columns and IPv6 interface columns are configured over a PPP link-layer interface, the router terminates the PPP session only when the PPP client exceeds the configured maximum number of renegotiation attempts for both the IPv4 interface and the IPv6 interface.
Example 1—Sets the maximum number of LCP renegotiation attempts to 5host1(config-if)#ppp max-negotiations lcp 5
Example 2—Sets the maximum number of IPCP renegotiation attempts to 30 (the default)host1(config-if)#ppp max-negotiations ipcp
Example 3—Sets the maximum number of LCP, IPCP, and IPv6CP renegotiation attempts to 15host1(config-if)#ppp max-negotiations 15
Example 4—Restores the maximum number of LCP, IPCP, and IPv6CP renegotiation attempts to the default value, 30host1(config-if)#no ppp max-negotiations
Use the no version to restore the default value, 30 renegotiation attempts.
See ppp max-negotiations.

ppp mru

Use to control the negotiation of the maximum receive unit (MRU).
Specify the number of bytes, in the range 64–65535.
We recommend you coordinate this value with the network administrator on the other end of the line.
If the value configured for the PPP MRU is greater than the value of the lower-layer MRU minus the PPP header length, the router logs a warning message and uses the lesser of the configured MRU value or the lower-layer MRU value minus the PPP header length to negotiate the local MRU.
If the value configured for the PPP MRU conflicts with a similar value configured for another protocol, such as the MTU value for PPPoE, the router uses the lesser of the two values.
Examplehost1(config-if)#ppp mru 576
Use the no version to restore the default value, which causes PPP to use the lower-layer MRU minus the PPP header length as the MRU value.
See ppp mru.

ppp passive-mode

Use to force a static or dynamic PPP interface into passive mode before LCP negotiation begins, for a period of one second. This delay enables slow clients to start up and initiate the LCP negotiation.
Examplehost1(config-if)#ppp passive-mode
Use the no version to disable passive mode.
See ppp passive-mode.

ppp peer

Use to resolve conflicts when the router and the PPP peer have the primary and secondary DNS and WINS name server addresses configured with different values.
By default, the DNS and WINS addresses configured on the router take precedence.
Use the dns keyword or the wins keyword to configure which PPP peer address takes precedence. This command has no effect unless both routers have the address configured and the address is in conflict. If the PPP peer has the address and the router does not, the peer always supplies the address regardless of how you have configured the PPP peer.
Examplehost1(config-if)#ppp peer dns
Use the no version when you want the router to take precedence during setup negotiations between the router and the peer. If the IP addresses that the peer sends to the router differ from the ones configured on your router, the router returns the values that you configured as the correct values to the peer.
See ppp peer.

ppp shutdown

ppp shutdown ip

ppp shutdown ipv6

ppp shutdown mpls

ppp shutdown osi

Use to terminate a PPP session.
To administratively disable the interface, use the ppp shutdown command.
To administratively disable IPCP, use the ppp shutdown ip command.
To administratively disable IPv6CP, use the ppp shutdown ipv6 command.
To administratively disable MPLS, use the ppp shutdown mpls command.
To administratively disable OSINLCP, use the ppp shutdown osi command.
All PPP sessions are enabled by default.
Examplehost1(config-if)#ppp shutdown
Use the no version to restart a disabled session.
See ppp shutdown.

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