This area lists added capacity and facts to annular out the advantage of the capacity in this chapter.
Unlike best of the Cisco Press Assay Certification Guides, this “Foundation Summary” does not
repeat advice presented in the “Foundation Topics” area of the chapter. Please booty the
time to apprehend and abstraction the capacity in the “Foundation Topics” area of the chapter, as able-bodied as
review items acclaimed with a Key Topic icon.
Table 4-14 lists and briefly explains several variations on NAT.
Table 4-15 lists the protocols mentioned in this affiliate and their corresponding standards documents.
Table 4-14 Variations on NAT
Name Function
Static NAT Statically correlates the aforementioned accessible IP abode for use by the aforementioned bounded host
every time. Does not conserve IP addresses.
Dynamic NAT Pools the accessible accessible IP addresses, aggregate amid a accumulation of bounded hosts, but
with alone one bounded host at a time application a accessible IP address. Does not conserve
IP addresses.
Dynamic NAT with
overload (PAT)
Like activating NAT, but assorted bounded hosts allotment a distinct accessible IP abode by
multiplexing application TCP and UDP anchorage numbers. Conserves IP addresses.
NAT for overlapping
address
Can be done with any of the aboriginal three types. Translates both antecedent and
destination addresses, instead of aloof the antecedent (for packets activity from
enterprise to the Internet).
Table 4-15 Protocols and Standards for Affiliate 4
Name Standardized In
IP RFC 791
Subnetting RFC 950
NAT RFC 1631
Private acclamation RFC 1918
CIDR RFCs 1517–1520
Foundation Arbitrary 121
Table 4-16 lists and describes some of the best frequently acclimated IOS commands accompanying to the
topics in this chapter.
Figure 4-8 shows the IP attack format.
Table 4-16 Command Reference for Affiliate 4
Command Description
ip abode ip-address affectation [secondary] Interface subcommand to accredit an IPv4 address
ip nat {inside | outside} Interface subcommand; identifies central or outside
part of network
ip nat central antecedent {list {access-list-number |
access-list-name} | route-map name} {interface
type cardinal | basin pool-name} [overload]
Global command that defines the set of inside
addresses for which NAT will be performed, and
corresponding alfresco addresses
ip nat central destination account {access-listnumber
| name} basin name
Global command acclimated with destination NAT
ip nat alfresco antecedent {list {access-list-number |
access-list-name} | route-map name} basin poolname
[add-route]
Global command acclimated with both destination and
dynamic NAT
ip nat basin name start-ip end-ip {netmask
netmask | prefix-length prefix-length}[type
rotary]
Global command to actualize a basin of addresses for
dynamic NAT
show ip nat statistics Lists counters for packets and for NAT table entries,
as able-bodied as basal agreement information
show ip nat translations [verbose] Displays the NAT table
clear ip nat adaptation {* | [inside global-ip
local-ip] [outside local-ip global-ip]}
Clears all or some of the activating entries in the
NAT table, depending on which ambit are used
debug ip nat Issues log letters anecdotic anniversary packet whose
IP abode is translated with NAT
show ip interface [type number] [brief] Lists advice about IPv4 on interfaces
122 Affiliate 4: IP Addressing
Figure 4-8 IP Header
Table 4-17 lists the agreement and meanings of the fields central the IP header.
Table 4-17 IP Attack Fields
Field Meaning
Version Version of the IP protocol. Best networks use IPv4 today, with IPv6 acceptable more
popular. The attack architecture reflects IPv4.
Header Breadth Defines the breadth of the IP header, including alternative fields. Because the breadth of
the IP attack charge consistently be a assorted of 4, the IP attack breadth (IHL) is multiplied
by 4 to accord the absolute cardinal of bytes.
DS Acreage Differentiated Services Field. This byte was originally alleged the Blazon of Account (ToS)
byte, but was redefined by RFC 2474 as the DS Field. It is acclimated for appearance packets for
the purpose of applying altered affection of account (QoS) levels to altered packets.
Packet Breadth Identifies the absolute breadth of the IP packet, including the data.
Identification Acclimated by the IP packet breach process. If a distinct packet is burst into
multiple packets, all $.25 of the aboriginal packet accommodate the aforementioned identifier, so
that the aboriginal packet can be reassembled.
Flags 3 $.25 acclimated by the IP packet breach process.
Fragment Offset A cardinal set in a fragment of a beyond packet that identifies the fragment’s location
in the beyond aboriginal packet.
Time to Live
(TTL)
A amount acclimated to anticipate acquisition loops. Routers cutback this acreage by 1 anniversary time
the packet is forwarded; already it decrements to 0, the packet is discarded.
Protocol A acreage that identifies the capacity of the abstracts allocation of the IP packet. For example,
protocol 6 implies a TCP attack is the aboriginal affair in the IP packet abstracts field.
Version
Identification Flags (3) Fragment Offset (13)
Time to Live Agreement Attack Checksum
Source IP Address
Destination IP Address
Optional Header
Fields and Padding
DS Field
0 8 16 24 32
Packet Length
Header
Length
Memory Builders 123
Table 4-18 lists some of the added accepted IP agreement acreage values.
Memory Builders
The CCIE Acquisition and Switching accounting exam, like all Cisco CCIE accounting exams, covers a fairly
broad set of topics. This area provides some basal accoutrement to advice you exercise your anamnesis about
some of the broader capacity covered in this chapter.
Fill in Key Tables from Memory
Appendix E, “Key Tables for CCIE Study,” on the CD in the aback of this book contains abandoned sets
of some of the key arbitrary tables in anniversary chapter. Print Appendix E, accredit to this chapter’s tables
in it, and ample in the tables from memory. Accredit to Appendix F, “Solutions for Key Tables for CCIE
Study,” on the CD to analysis your answers.
Field Meaning
Header
Checksum
A amount acclimated to abundance a anatomy analysis arrangement (FCS) value, whose purpose is
to actuate if any bit errors occurred in the IP attack (not the data) during
transmission.
Source IP
Address
The 32-bit IP abode of the sender of the packet.
Destination IP
Address
The 32-bit IP abode of the advised almsman of the packet.
Optional Header
Fields and
Padding
IP supports added attack fields for approaching amplification via alternative headers. Also,
if these alternative headers do not use a assorted of 4 bytes, added bytes are added,
comprised of all bifold 0s, so that the attack is a assorted of 4 bytes in length.
Table 4-18 IP Agreement Acreage Values
Protocol Name Agreement Number
ICMP 1
TCP 6
UDP 17
EIGRP 88
OSPF 89
PIM 103
Table 4-17 IP Attack Fields (Continued)
124 Affiliate 4: IP Addressing
Definitions
Next, booty a few moments to abode bottomward the definitions for the afterward terms:
subnet, prefix, classless IP addressing, classful IP addressing, CIDR, NAT, IPv4,
subnet advertisement address, subnet number, subnet zero, advertisement subnet, subnet
mask, clandestine addresses, SLSM, VLSM, Central Bounded address, Central Global address,
Outside Bounded address, Alfresco Global address, PAT, overloading, quartet
Refer to the comment to analysis your answers.
Further Reading
All capacity in this affiliate are covered to capricious abyss for the CCNP Acquisition exam. For more
details on these topics, accredit to CCNP BSCI Official Assay Certification Guide, Fourth Edition, and
Authorized Self-Study Guide: Building Scalable Cisco Internetworks (BSCI), Third Edition.