Tài liệu giảng dạy CCNA - module 7-1 - NAT PAT DHCP

Table of Content1 Scaling networks with Network Address Translation and Port Address Translation 2 Dynamic Host Configuration Protocol... Introducing NAT and PAT  Cisco defines the fol

NAT/PAT/DHCP

Table of Content

1 Scaling networks with Network Address Translation and

Port Address Translation

2 Dynamic Host Configuration Protocol

SCALING NETWORKS WITH NAT

AND PAT

Private addressing

 10.0.0.0 – 10.255.255.255

 172.16.0.0 – 172.31.255.255

 192.168.0.0 – 192.168.255.255

Introducing NAT and PAT

 Cisco defines the following NAT terms:

 Inside local address

 Inside global address

 Outside local address

 Outside global address

Major NAT and PAT features

 Static NAT is designed to allow one-to-one mapping of local and global addresses

 Dynamic NAT is designed to map a private IP address to a public address Any IP address from a pool of public IP addresses is assigned to a network host

 Port Address Translation (PAT), maps multiple private IP addresses to a single public IP address

Configuring static NAT

Router(config)# ip nat inside source static 10.1.1.2 171.69.68.10

Router(config)# interface ethernet 0

Router(config-if)# ip nat inside

Router(config)# interface serial 0

Router(config-if)# ip nat outside

Configuring dynamic NAT/PAT

 Define private IP addresses range:

Router(config)# access-list 1 permit 10.0.0.0 0.0.255.255

 Define public IP addresses pool:

Router(config)# ip nat pool cisco 179.9.8.0 netmask 255.255.255.240

 Establish dynamic source translation:

Router(config)# ip nat inside source list 1 pool cisco overload

 Specify the inside and outside interface.

Verifying PAT configuration

 Clear ip nat translation *

 Clear ip nat translation inside global-ip local-ip outside local-ip global-ip

 Show ip nat translation

 Show ip nat statistics

Troubleshooting NAT and PAT

configuration

1 Based on the configuration, clearly define what NAT is supposed to achieve

2 Verify that correct translations exist in the translation table

3 Verify the translation is occurring by using show and debug commands

4 Review in detail what is happening to the packet and verify that routers have the correct routing information to move the packet along

Issues with NAT

 NAT conserves the legally registered addressing scheme

 NAT increases the flexibility of connections to the public network

 Consistency of the internal network addressing scheme

 NAT increases delay

Issues with NAT (cont.)

 Cisco IOS NAT does not support the following traffic types:

 Routing table updates

 DNS zone transfers

 BOOTP

 talk and ntalk protocols

 Simple Network Management Protocol (SNMP)

DHCP

Introducing DHCP

 Dynamic Host Configuration Protocol (DHCP) works in a client/server mode DHCP enables DHCP clients on an IP network to obtain their configurations from a DHCP server

 A DHCP client is included in most modern operating systems including the various Windows operating systems, Novell Netware, Sun Solaris, Linux, and MAC OS

BOOTP and DHCP differences

Both protocols are client/server based and use UDP ports

DHCP server

IP1 IP2

IP Address Gateway

IP of servers

IP Address Gateway

IP of servers

 Specify the excluded IP addresses range:

Verifying and troubleshooting DHCP

operation

 show ip dhcp binding

 show ip dhcp server statistics

 debug ip dhcp server events

IP SRC: ?

IP DST: 255.255.255.255

UDP 67

CIADDR: ? GIADDR: ? MASK: ? CHADDR: MAC A

DHCP relay (cont.)

E0: 192.168.1.1/24

Ip helper-address 192.168.2.254

E1: 192.168.2.1/24 IP???

A

SRC MAC: E0 DST MAC: MAC A

IP SRC: 192.168.2.254

IP DST: 192.168.1.10

UDP 68

CIADDR: 192.168.1.10 GIADDR: 192.168.1.1 MASK: 255.255.255.0 CHADDR: MAC A

SRC MAC:MAC SERV DST MAC: E1

IP SRC: 192.168.2.254

IP DST: 192.168.1.10

UDP 68

CIADDR:192.168.1.10 GIADDR: 192.168.1.1 MASK: 255.255.255.0 CHADDR: MAC A

 Private addresses are for private, internal use and should never

be routed by a public Internet router

 NAT alters the IP header of a packet so that the destination

address, the source address, or both addresses are replaced with

different addresses

 PAT uses unique source port numbers on the inside global IP

address to distinguish between translations

 NAT and PAT may be configured for static translation, dynamic

translation, and overloading

 DHCP works in a client/server mode, enabling clients to obtain IP