Appendix B PPTP and GRE Tunneling Through NAT

Transcription

1 Appendix B PPTP and GRE Tunneling Through NAT This appendix describes Point-to-Point Tunneling Protocol (PPTP) and Generic Routing Encapsulation (GRE) tunneling through Network Address Translation (NAT). It supplements information in the following JUNOSe Release 6.1.x guides: JUNOSe IP Services Configuration Guide, Chapter 11, Configuring Layer 2 Services over GRE JUNOSe IP Services Configuration Guide, Chapter 3, Configuring NAT JUNOSe Command Reference Overview You can configure NAT traversal support for GRE flows using simple translations (Basic NAT). Because PPTP uses an enhanced GRE encapsulation for the PPP payload, configuring for GRE flows also supports NAT traversal for PPTP tunnels. NOTE: Neither port translation (NAPT) nor Firewall traversal for GRE packets is supported for GRE flows. When configured, the following types of translations are supported for GRE and PPTP tunnels: Inside source static simple translations (inbound and outbound) Outside source static simple translations (inbound and outbound) Inside source dynamic simple translations (inbound and outbound) Outside source dynamic simple translations (inbound and outbound) Combinations of the preceding translations (for example, twice NAT) Overview 61

2 JUNOSe Release Notes Packet Discard Rules For all supported types of traffic (TCP, UDP, ICMP, and GRE), NAT discards packets in the following cases: When the translation table is full (that is, no more entries can be added). When the address pool is exhausted for outbound packets with inside source dynamic translation. When no match can be found for the destination addresses of inbound packets. When the address pool is exhausted for inbound packets with outside source dynamic translation. In addition, NAT discards GRE packets under the following conditions: When the GRE packets match an NAPT rule. When Firewall is functioning. Tunnel Configurations Through NAT PPTP uses enhanced GRE encapsulation for PPP payloads. After the PPTP tunnel setup process, PPP packets are exchanged using GRE encapsulation. It is critical that a NAT device that resides between PPTP client and PPTP server allow GRE flows. This section contains NAT configuration examples for both inside and outside PPTP tunnel setup through NAT. Clients on an Inside Network In this example, a subscriber on the inside network is initiating PPTP tunnels to a PPTP server located in the outside network. The PPTP connection to the server traverses an E-series router that has NAT enabled. Figure 1: PPTP Tunnels on an Inside Network Inside interface Outside interface PPTP server PPTP client PPTP request SA = DA = Inside source static simple translation installed PPTP request SA = DA = g Packet Discard Rules

3 Appendix B: PPTP and GRE Tunneling Through NAT The router has installed an inside source static simple translation in its translation table as follows: Inside Local Address Inside Global Address The PPTP client initiates its tunnels to the server at The E-series router translates the SA from inside local to inside global SA Because GRE traffic can pass through NAT, all matching PPTP control packets are translated and forwarded to the destination. Clients on an Outside Network In this example, an outside subscriber initiates PPTP tunnels to a PPTP server located in the service provider network. The PPTP connection to the server traverses an E-series router that has NAT enabled. Figure 2: PPTP Tunnels on an Outside Network Outside interface Inside interface PPTP client Access network PPTP server PPTP request SA = DA = Inside source static simple translation installed g The router has installed an inside source static simple translation in its translation table as follows: Inside Local Address Inside Global Address The PPTP client initiates its tunnels to the inside global address The E-series router translates packets destined for address and forwards them to the inside local address of Because GRE traffic can pass through NAT, all matching PPTP control packets are translated and forwarded to the destination. Tunnel Configurations Through NAT 63

4 JUNOSe Release Notes GRE Flows Through NAT Because PPTP requires the use of GRE flows, the examples in the previous section also work for any GRE traffic flows that traverse NAT. GRE flows can terminate at an E-series router if NAT is or is not enabled. When the router receives locally terminating inbound GRE packets, the router transmits the packets to the tunnel server module for GRE processing. If the packets require translating, they are again sent through the tunnel server module. NOTE: Only inner IP headers are translated for terminating GRE flows; outer IP headers are never translated. For outbound GRE packets, the process works in reverse. If the packets require translation, the router transmits the packets to the tunnel server module for translation. If the packets are destined for a GRE tunnel, they are again sent through the tunnel server module where an outer header is prepended to the packet and the packet is then sent to the appropriate GRE tunnel. Displaying Translation Entries The show ip nat translations command displays current translations that reside in the translation table. Simple translation entries appear with inside/outside and local/global address information. Extended entries appear with added protocol and port numbers (or query ID). Using verbose mode additionally provides the time since creation and time since last use for each translation entry. show ip nat translations Use to display current translations that reside in the NAT translation table. Field descriptions Prot Protocol (TCP, UDP, ICMP, or GRE) for this translation entry; this field appears only for extended table entries Inside local Inside local IP address for this translation entry; this field also provides the port number, separated by a colon ( : ) for extended entries Inside global Inside global IP address for this translation entry; this field also provides the port number, separated by a colon ( : ) for extended entries Outside global Outside global IP address for this translation entry; this field also provides the port number, separated by a colon ( : ) for extended entries Outside local Outside local IP address for this translation entry; this field also provides the port number, separated by a colon ( : ) for extended entries 64 GRE Flows Through NAT

5 Appendix B: PPTP and GRE Tunneling Through NAT Time since creation Amount of time elapsed since the translation entry appeared in the translation table (hh:mm:ss format) Time since last use Amount of time elapsed since the translation entry was used (hh:mm:ss format) Example 1 host1#show ip nat translations Prot Inside local Inside global Outside global Outside local GRE :* :* ICMP : : TCP : : NOTE: Because they are not NAPT translations, port numbers for GRE translations appear as asterisks (*). Example 2 host1#show ip nat translations verbose Time Time Inside Outside Outside since since Prot Inside local global global local creation last use :04:50 00:00: :02:12 00:00: :02:12 00:00: :03:24 Never :01:44 00:00: :01:44 00:00:01 UDP : :8 00:03:10 Never UDP : : :02:12 00:00: UDP : : :02:12 00:00: TCP : :8 00:03:10 Never UDP : : :03:35 Never 108 Displaying Translation Entries 65

6 JUNOSe Release Notes Commands in the JUNOSe Command Reference This section presents commands that have been modified for this release and are relevant to features that are presented in this release. ip nat translation Description Changes or disables translation timeouts, per virtual router, for existing and newly created translations in the translation table. All timeouts for this command support a range of seconds (about 25 days). The no version enables the timer using its default value. NOTE: GRE translations are used as optimizations to discard GRE traffic. You can use the gre-timeout keyword to control GRE aging timeout, even though we do not support NAPT for GRE. The GRE aging timer has no effect on any simple translations GRE might use. Syntax ip nat translation { timeout udp-timeout dns-timeout tcp-timeout finrst-timeout icmp-timeout gre-timeout } seconds no ip nat translation { timeout udp-timeout dns-timeout tcp-timeout finrst-timeout icmp-timeout gre-timeout} timeout Sets aging time for dynamic translations (except for overloaded translations); default value is seconds (24 hours) udp-timeout Sets aging time for UDP protocol translations; default value is 300 seconds (5 minutes) dns-timeout Sets aging time for DNS protocol translations (port 53 on TCP or UDP); default value is 60 seconds tcp-timeout Sets aging time for TCP protocol translations; default value is seconds (24 hours) first-timeout Sets aging time for TCP connections terminated with RST or FIN flags; default value is 60 seconds icmp-timeout Sets aging time for ICMP protocol translations; default value is 300 seconds (5 minutes) gre-timeout Sets aging time for GRE protocol translations; default value is 300 seconds (5 minutes) seconds Number of seconds before the router removes an unused NAT table entry Mode Global Configuration 66 Commands in the JUNOSe Command Reference

7 Appendix B: PPTP and GRE Tunneling Through NAT clear ip nat translation Description Clears all or the specified NAT table entries. There is no no version. Syntax clear ip nat translation * clear ip nat translation inside insideglobalipaddress insidelocalipaddress clear ip nat translation outside outsidelocalipaddress outsideglobalipaddress clear ip nat translation { tcp udp icmp} inside insideglobalipaddress insideglobalport insidelocalipaddress insidelocalport clear ip nat translation { tcp udp icmp gre } inside insideglobalipaddress * insidelocalipaddress * clear ip nat translation { tcp udp icmp } inside insideglobalipaddress insideglobalport insidelocalipaddress insidelocalport outside outsidelocalipaddress outsidelocalport outsideglobalipaddress outsideglobalport * Clears all translations when used in the clear ip nat translation command * Matches any global or local port to remove inside source extended TCP, UDP, ICMP or GRE translations for the specified global IP address and local IP address when used in the clear ip nat translation { tcp udp icmp gre } inside insideglobalipaddress * insidelocalipaddress * command inside Specifies an inside address insideglobalipaddress Inside global IP address insidelocalipaddress Inside local IP address outside Specifies an outside address outsidelocalipaddress Outside local IP address outsideglobalipaddress Outside global IP address tcp Specifies a TCP port translation udp Specifies a UDP port translation icmp Specifies an ICMP port translation gre Specifies a GRE translation insideglobalport Inside global port number insidelocalport Inside local port number outsideglobalport Outside global port number outsidelocalport Outside local port number Mode Privileged Exec Commands in the JUNOSe Command Reference 67

8 JUNOSe Release Notes show ip nat translations Description Displays translations that reside in the NAT translation table. Syntax show ip nat translations [ static dynamic ] [ tcp udp icmp gre ]* [ verbose ] [ filter ] show ip nat translations inside insidelocalipaddress [ localport ] [ insideglobalipaddress [ globalport ] ] [ verbose ] [ filter ] show ip nat translations outside outsideglobalipaddress [ globalport ] [ outsidelocalipaddress [ localport ] ] [ verbose ] [ filter ] static Displays static translations dynamic Displays dynamic translations tcp Displays TCP port translations udp Displays UDP port translations icmp Displays ICMP port translations gre Displays GRE translations * Indicates that one or more parameters can be repeated multiple times in a list in the command line inside Specifies an inside address insideglobalipaddress Inside global IP address insidelocalipaddress Inside local IP address outside Specifies an outside address outsidelocalipaddress Inside local IP address outsideglobalipaddress Inside global IP address localport Local port value globalport Global port value verbose Additionally displays the time since creation and time since last use for each translation entry filter See Filtering show Commands in About This Guide Mode User Exec 68 Commands in the JUNOSe Command Reference