on-demand delivery of real-time data, such as audio and video. Sources of data can include both live data
feeds and stored clips.
PPTP-ALG
PPTP is a network protocol that enables secure transfer of data from a remote client to a private enterprise
server by creating a Virtual Private Network (VPN). It is used to provide IP security at the network layer.
PPTP uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets.
PPTP-ALG is a CGN solution that allows traffic from all clients through a single PPTP tunnel.
A PPTP tunnel is instantiated on the TCP port. This TCP connection is then used to initiate and manage a
second GRE tunnel to the same peer.
PPTP uses an access controller and network server to establish a connection.
PPTP Access Controller (PAC)
A device attached to one or more PSTN or ISDN lines capable of PPP operation and handling the PPTP
protocol. It terminates the PPTP tunnel and provides VPN connectivity to a remote client.
PPTP Network Server (PNS)
A device which provides the interface between the Point-to-Point Protocol (encapsulated in the PPTP protocol)
and a LAN or WAN. The PNS uses the PPTP protocol to support tunneling between a PPTP PAC and the
PNS. It requests to establish a VPN connectivity using PPTP tunnel.
Control Connection
A control connection is established between a PAC and a PNS for TCP.
Tunnel
A tunnel carries GRE encapsulated PPP datagrams between a PAC and a PNS
Active FTP, PPTP ALG, and RTSP ALG are supported on NAT44 applications. Active FTP and RTSP
ALG are supported on DS-Lite applications.
Note
TCP Maximum Segment Size Adjustment
When a host initiates a TCP session with a server, the host negotiates the IP segment size by using the maximum
segment size (MSS) option. The value of the MSS option is determined by the maximum transmission unit
(MTU) that is configured on the host.
Static Port Forwarding
Static port forwarding helps in associating a private IP address and port with a statically allocated public IP
and port. After you have configured static port forwarding, this association remains intact and does not get
removed due to timeouts until the CGSE is rebooted. In case of redundant CGSE cards, it remains intact until
both of the CGSEs are reloaded together or the router is reloaded. There are remote chances that after a reboot,
this association might change. This feature helps in cases where server applications running on the private
network needs access from public internet.
Cisco IOS XR Carrier Grade NAT Configuration Guide for the Cisco CRS Router, Release 5.2.x
OL-32659-01 17
Implementing Carrier Grade NAT on Cisco IOS XR Software
TCP Maximum Segment Size Adjustment
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