Title: CIS460
1CIS460 NETWORK ANALYSIS AND DESIGN
- CHAPTER 6
- Designing Models for Addressing and Naming
2Overview
- Look at the guidelines for assigning addresses
and names to internetwork components, including
networks, subnets, routers, servers, and end
systems - Importance of using a structured model for
network layer addressing and naming - Importance of developing policies and procedures
for addressing and naming
3Guidelines for Assigning Network-Layer Address
- Should be planned, managed and documented
- Rules for network-layer addressing
- Design a structured model
- Leave room for growth
- Assign blocks of addresses in a hierarchical
fashion - Use meaningful numbers
- Delegate authority if possible to regional/branch
- use dynamic addressing
- use private addresses with network address
translation
4Using a Structured Model for Network-Layer
Addressing
- Addresses are meaningful, hierarchical, and
planned - A clearly documented structured model facilitates
management and troubleshooting - With no model problems can occur
- Duplicate network and host addresses
- illegal addresses that cannot route on internet
- insufficient addresses
- addresses that cannot be used
5Using Meaningful Network Numbers
- In AppleTalk assign cable range for each network
segment - e.g., building number/floor number
- In Novell NetWare each network segment is
assigned a 4-byte hexadecimal number - Using building and floor numbers allow
identifying and narrowing location of problems
6Administering Addresses by a Central Authority
- Corporate IS or enterprise network department
should develop a global model for network-layer
addressing - In an IP environment can request block of numbers
from an ISP or Internet Assigned Numbers
Authority - If from ISP request a large enough block for
scalability - Use private addresses as an alternative
7Distributing Authority for Addressing
- Determine who is to implement model
- if inexperienced networks administrators then
keep it simple - If branch/regional offices inexperienced then
keep authority centralized
8Using Dynamic Addressing for End Systems
- Reduces the configuration tasks required to
connect end systems - Supports users who change offices frequently
- Built into desktop protocols such as AppleTalk
and Novell NetWare - Minimizes configuration tasks
9AppleTalk Dynamic Addressing
- Network layer stations address consists of a
16-bit network number and an 8-bit node ID - Once network-layer address is chosen it is saved
in battery-backed-up RAM so it doesnt have to
get new address each time it boots - AppleTalk station communicates with a router to
determine the cable range for its network segment
10Novell NetWare Dynamic Addressing
- Station address consists of 4 byte network number
and a 6-byte node ID. - 6-byte node ID is the same as the stations MAC
address - A network manage configures routers and servers
on a NetWare network with the 4 byte network
number for a network segments
11IP Dynamic Addressing
- An IP layer address is 4 bytes in length and
consists of a prefix and host part - In the past each host was required to be
configured manually. Now addressing is done
dynamically through - Reverse Address Resolution Protocol (RARP) and
BOOTP - BOOTP is more sophisticated than RARP and returns
additional information including address of
default router
12The Dynamic Host Configuration Protocol (DHCP)
- DHCP is based on BOOTP
- BOOTP hosts interoperate with DHCP
- DHCP adds many enhancements to BOOTP including
larger vendor specific information field and
automatic allocation of reusable network-layer
address - DHCP uses a client/server model
- Servers allocate network-layer addresses and save
information about which addresses are used
13The Dynamic Host Configuration Protocol (DHCP)
(Contd)
- DHCP supports three methods for IP address
allocation - Automatic allocation - assigns permanent IP
address to a client - Dynamic allocation - assigns an IP address to a
client for a limited period of time - Manual - network administrator assigns
permanently and DHCP merely conveys address
information
14The Dynamic Host Configuration Protocol (DHCP)
(Contd)
- Dynamic is most popular where hosts are not on
all of the time. Address given for a short
period time called a lease - Can reuse address if lease has expired
- Chen client boots it broadcasts a DHCP discover
message on its local subnet - each server responds with a DHCP offer message
15The Dynamic Host Configuration Protocol (DHCP)
(Contd)
- Client choose one server response to request
configuration parameters - Server selected commits configuration parameters
to persistent storage and responds with DHCP ACK
message - If no response received client times out and
resends a DHCP discover and request messages
16Using Private Addresses in an IP Environment
- These are addresses assigned by internal networks
and hosts without any coordination from an ISP or
the Internet Assigned Numbers Authority - An advantage is security. Private numbers are
not advertised on the Internet - Helps meet goals for adaptability and flexibility
17Using Private Addresses in an IP Environment
(Contd)
- Network can advertise just one network number or
small block of numbers to the Internet - Can reserve scarce Internet addresses for public
servers
18Caveats with Private Addressing
- Outsourcing network management is difficult
- Difficulty of communicating with partners,
vendors, suppliers, and other outsiders - Easy to forget to use a structured model
- Assign in a structured, hierarchical fashion
19Network Address Translation (NAT)
- An IP mechanism that is used for converting
addresses from an inside network to addresses
that are appropriate for an outside network and
vice-versa - NAT administrator configures a pool of outside
addresses that can be used for translation
20Network Address Translation (NAT) (Contd)
- Some NAT products offer port translation for
mapping several addresses to the same address - When using NAT all traffic must go through a NAT
gateway - Must also modify IP addresses that occur inside
the data part of a packet
21Using a Hierarchical Model for Assigning Addresses
- Hierarchical addressing is a model for applying
structure to addresses so that numbers in the
left part of an address refer to large blocks of
networks or nodes, and numbers in the right part
of an address refer to individual networks or
nodes
22Why Use a Hierarchical Model for Addressing and
Routing
- Support for easy troubleshooting, upgrades and
manageability - Optimized performance
- Faster routing-protocol convergence
- Scalability
- Stability
- Fewer network resources need
23Why Use a Hierarchical Model for Addressing and
Routing (Contd)
- Permits summarization (aggregation) of network
numbers - Summarization allows a router to group many
network numbers when advertising its routing
table - Facilitates variable-length subnet masking (VLSM)
24Hierarchical Routing
- Means that knowledge of the network topology and
configuration is localized - No single router needs to understand how to get
to each other network segment - Addresses must be assigned in hierarchical fashion
25Classless Inter-Domain Routing
- The internet has a severe scalability problem
- Classless inter_domain Routing (CIDR) is a method
for summarizing routes - Addresses should be assigned in blocks
- Routers should group routes together to cut down
on the quantity of routing information shared by
Internet routers
26Classless Routing Versus Classful Routing
- IP address contains a prefix part and a host part
- Prefix identifies a block of host numbers and is
used for routing that block - Traditional (classful routing) does not transmit
any information about the prefix length - Traditional IP hosts and routers had a limited
capability to understand prefix lengths and
subnets
27Classless Routing Versus Classful Routing (Contd)
- Classless routing protocols transmit a prefix
length with an IP address - Classless routing protocols include Routing
Information Protocol (RIP) V2, Enhanced Interior
Gateway Routing Protocol (Enhanced IGRP), Open
Shortest Path First (OSPF), Border Gateway
Routing Protocol (BGP) Intermediate System-to
Intermediate System (IS-IS)
28Route Summarization (Aggregation)
- When advertising routes into another major
network classful routing protocols automatically
summarize subnets - Only advertise route to a Class A, B, or C
network instead of routes to subnets - Discontiguous subnets are not supported
- Classless routing protocols advertise a route and
a prefix length
29Route Summarization Tips
- For route summarization to work correctly
- Multiple IP addresses must share the same
left-most bits - Routers must base their routing decisions on a
32-bit IP address and prefix length that can be
up to 32 bits - routing protocols must carry the prefix length
with 32-bit addresses
30Discontiguous Subnets
- Subnets must be next to each other to be
supported - Classless routing protocol can be used to route
to discontiguous subnets
31Mobile Hosts
- Classless routing and discontiguous subnets
support mobile hosts - A mobile host is a host that moves from one
network to another and has a statically-defined
IP address - Routers use the longest prefix available that is
appropriate for the destination address in the
packet
32Variable-Length Subnet Masking
- Using classless routing means that you can have
different sizes of subnets within a single
network - Variable length subnet masking (VLSM) relies on
providing prefix length information explicitly
with each use of an address - It is important to avoid inadvertently
overlapping blocks of addresses
33Designing a Model for Naming
- Short meaningful names enhance user productivity
and simplify network management - A good naming model strengthens the performance
and availability of a network - It should let a user transparently access a
service by name rather than address - The system should map the name to the address
34Distributing Authority for Naming
- No department should be burdened with assigning
and maintaining all names - If device has local name server instead of
depending on a centralized server many names can
be resolved to addresses locally without causing
traffic on the internetwork
35Guidelines for Assigning Names
- Should be short, meaningful, unambiguous and
distinct - Users should recognize which name goes with which
device - Can use three letter prefixes
- Some networks use geographical names
- Avoid names with unusual characters
- Avoid case sensitivity
36Assigning Names in an AppleTalk Environment
- You assign names to shared servers and printers
- Use meaningful names
- can also assign names to zones. A zone is a
collection of nodes that share information
37Assigning Names in a Novell NetWare Environment
- Assign names to resources such as volumes on a
file server, shared printers, print queues,
printer servers and possibly other servers - Generally no need to assign names to end systems
38Assigning Names in a NetBIOS Environment
- Is a session-layer protocol that includes
functions for naming devices which ensures the
unique of names and finding named services
39NetBIOS in a Bridged or Switched Environment
(NetBEUI)
- NetBIOS was originally implemented as session
layer software that runs on top of the driver for
a NIC - Makes extensive use of broadcast packets for
naming functions - When started it broadcasts check-name queries to
make sure its name is unique - Can have as many as 32 names
40NetBIOS in a Novell NetWare Environment (NWLink)
- With NWLink NetBIOS runs on top of Novells
Sequenced Packet Exchange and Internetwork Packet
Exchange protocols - Uses type-20 broadcast packets to send name
registration
41NetBIOS in a TCP/IP Environment (NetBT)
- In this protocol you have 4 options for name
registration and lookup - Broadcasts - used to announce services
- Lmhosts files - a lmhosts file is place on each
station. Not dynamic - Windows Internet Name Service (WINS) - use WINS
server to resolve a name - Domain Name System (DNS) - standard internet
service which uses a generic IP environment
42Assigning Names in an IP Environment
- Accomplished by configuring hosts files, DNS
servers, or Network Information Service (NIS)
servers.
43The Domain Name System
- Developed in early 1980s to manage a hosts file
containing the names and addresses of all the
systems on the Internet - com, edu, gov, etc
- Can also include geographical level domains