IntroductionThis document provides answers to frequently asked questions about Network Address Translation (NAT). Show
Generic NATQ. What is NAT?
Q. How does NAT work?
Q. How do I configure NAT?
Q. What are the main differences between the Cisco IOS® Software and Cisco PIX Security Appliance implementations of NAT?
Q. On which Cisco routing hardware is Cisco IOS NAT available? How can the hardware be ordered?
Q. Does NAT occur before or after routing?
Q. Can NAT be deployed in a public wireless LAN environment?
Q. Does NAT do TCP load-balancing for Servers on the internal network?
Q. Can I rate limit the number of NAT translations?
Q. How is routing learned or propagated for IP subnets or addresses that are used by NAT?
Q. How many concurrent NAT sessions are supported in Cisco IOS NAT?
Q. What kind of routing performance can be expected when using Cisco IOS NAT?
Q. Can Cisco IOS NAT be applied to subinterfaces?
Q. Can Cisco IOS NAT be used with Hot Standby Router Protocol (HSRP) to provide redundant links to an ISP?
Q. Does Cisco IOS NAT support inbound translations on a Frame Relay interface? Does it support outbound translations on the Ethernet side?
Q. Can a single NAT-enabled router allow some users to use NAT and other users on the same Ethernet interface to continue to use their own IP addresses?
Q. When configuring for PAT (overloading), what is the maximum number of translations that can be created per inside global IP address?
Q. How does PAT work?
Q. What are NAT IP pools?
Q. What is the maximum number of configurable NAT IP pools (ip nat pool "name")?
Q. What is the advantage of using route-map vs ACL on a NAT pool?
Q. What is IP address "overlapping" within the context of NAT?
Q. What are static NAT translations?
Q. What is meant by the term NAT overloading; is this PAT?
Q. What are dynamic NAT translations?
Q. What is ALG?
Q. Is it possible to build a configuration with both static and dynamic NAT translations?
Q. When a traceroute is done through a NAT router, should traceroute show the NAT-Global address or should it leak the NAT-Local address?
Q. How does PAT allocate port?
Q. What is the difference between IP fragmentation and TCP segmentation?
Q. Does NAT support out-of-order for IP fragmentation and TCP segmentation?
Q. How to debug IP fragmentation and TCP segmentation?
Q. Is there a supported NAT MIB?
Q. What is TCP timeout, and how does it relate to the NAT TCP timer?
Q. Can I change the amount of time it takes for a NAT tranlation to time out from the NAT tranlation table?
Q. How do I stop Lightweight Directory Access Protocol (LDAP) from attaching extra bytes to each LDAP reply packet?
Q. What is the route recommendation for the inside global/outside local IP address on the NAT box ?
Q. Does Cisco IOS NAT support ACLs with a "log" keyword?
Voice-NATQ. Does NAT support Skinny Client Control Protocol (SCCP) v17 which is shipped with Cisco Unified Communications Manager (CUCM) V7?
Q. Which CUCM /SCCP/firmware load versions are supported by NAT?
Q. What is Service Provider PAT Port Allocation Enhancement for RTP and RTCP?
Q. What is Session Initiation Protocol (SIP) and can SIP packets be NATted?
Q. What is Hosted NAT Traversal support for Session Border Controller (SBC)?
Q. How many SIP, Skinny, and H323 calls can a routers memory and CPU handle with NAT?
Q. Does a NAT router suppport TCP segmentation of Skinny and H323 packets?
Q. Are there any caveats to watch out for when using a NAT overload configuration in a voice deployment?
Q. Are there any known problems caused by issuing the clear ip nat trans * command or the clear ip nat trans forced command in a voice deployment?
Q. Does NAT support voice co-located solution?
Q. Does NVI support Skinny ALG, H323 ALG, and TCP SIP ALG?
NAT with VRF/MPLSQ. Will a NAT router ever support NATting the same address space in a VRF as is being NATted in a global address space? Currently, I receive this warning: "% similar static entry (1.1.1.1 ---> 22.2.2.2) already exists" when I attempt to configure the following: 72UUT(config)#ip nat inside source static 1.1.1.1 22.2.2.2 72UUT(config)#ip nat inside source static 1.1.1.1 22.2.2.2 vrf RED
Q. Does legacy NAT support VRF-Lite (NATting from a VRF to a different VRF)?
NAT NVIQ. What is NAT NVI?
Q. Should NAT NVI be used when NATting between an interface in global and an interface in a VRF?
Q. Is TCP segmentation for NAT-NVI supported?
Q. Does NVI support Skinny ALG, H323 ALG, and TCP SIP ALG?
Q. Does TCP segmentation supported with SNAT?
SNATQ. What is Stateful NAT (SNAT)?
Q. Is TCP segmentation supported with SNAT?
Q. Is SNAT support for asymetric routing?
NAT-PT (v6 to v4)Q. What is NAT-PT?
Q. Is NAT-PT supported in the Cisco Express Forwarding (CEF) path?
Q. What ALGs are supported in NAT-PT?
Q. Does ASR 1004 support NAT-PT?
Platform-Dependent Cisco 7300/7600/6kQ. Is Stateful NAT (SNAT) available on Catalyst 6500 on the SX train?
Q. Is VRF-aware NAT supported in hardware on the 6k?
Q. Do the 7600 and Cat6000 support VRF-aware NAT?
Platform-Dependent Cisco 850Q. Does the Cisco 850 support Skinny NAT ALG in release 12.4T?
NAT DeploymentQ. How do I implement NAT?
Q. How do I implement NAT with voice?
Q. How do I integration NAT with MPLS VPNs?
Q. Does NAT static mapping support HSRP for high availability?
Q. How do I implemet NAT NVI?
Q. How do I implement load balancing with NAT?
Q. How do I implement NAT in conjucntion with IPSec?
Q. How do I implement NAT-PT?
Q. How do I implement multicast NAT?
Q. How do I implement stateful NAT (SNAT)?
NAT Best PracticesQ. Are there any NAT best practices?
Related Information
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