C HAPTER 6 Part 2 1 Revised sem2 2013-2014 -AAB-2013.
-
Upload
charlene-williams -
Category
Documents
-
view
218 -
download
2
Transcript of C HAPTER 6 Part 2 1 Revised sem2 2013-2014 -AAB-2013.
ROUTE SUMMARIZATION (AGGREGATION) When advertising routes into another major
network, classful routing protocols automatically summarize subnets. Classful only advertise a route to a Class A,B and C
network, instead of routes to subnets. Classful routers and hosts do no undertand nonlogical
prefix length and subnet. Why summarizing?
Reduce the size of routing table which minimizes bandwidth consumption and processing on routers.
It also able to keep the problem within one area of the network from spreading to other areas.
The automatic summarization into a major class network has disadvantages – discontiguous subnet is not supported. 2
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
SUPERNETTING/EXAMPLE OF ROUTE SUMMARIZATION
The network administrator assigned network numbers 172.16.0.0 through 172.19.0.0 to networks in a branch office.
3
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
172.16.0.0
172.17.0.0
172.18.0.0
172.19.0.0
Branch-Office Networks
Enterprise Core Network
Branch-Office Router
CONTINUE..
The branch office can summarize its local network numbers and report that it can reach 172.16.0.0/14.
By advertising this single route, the router is saying” route packets to me if the destinations has the first 14 bits set to 172.16- the first 14 bits are equal to 10101100000100
4
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
172.16.0.0/14 SUMMARIZATION
Second Octet in Decimal
Second Octet in Binary
16 00010000
17 00010001
18 00010010
19 00010011
5
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
• the leftmost 6 bits from 16 19 are identical.
ROUTE SUMMARIZATION TIPS
Multiple IP addresses must share the same leftmost 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.
6
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
CONTINUE..
Additions:When looking at a block of subnets, you can
determine if the addresses can be summarized by the following rules: The number of subnets to be summarized must
be must be a power of 2 (2,4,8 etc) The relevant octet in the first address in the
block to be summarized must be a multiple of the number of subnets
7
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
EXAMPLE
The following network numbers are defined at branch office. Can they be summarized? 192.168.32.0 192.168.33.0 192.168.34.0 192.168.35.0 192.168.36.0
8
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
DISCONTIGUOUS SUBNETS
• based on the above figure, both routers cannot reach remote subnets of network 10.0.0.0 since there are not connected. • solve it suing CIDR – a classless routing protocol. •Router A advertises that it can get to network 10.108.16.0/20. •Router B advertises that it can get to network 10.108.32.0/20•CIDR understand prefixes of any length , the routers can route to DS.
9
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
GUIDELINES FOR ASSIGNING NAMES Names should be
Short Meaningful Unambiguous Distinct Case insensitive
Avoid names with unusual characters Hyphens, underscores, asterisks, and so on
10
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
DOMAIN NAME SYSTEM (DNS)
Is a distributed database, supports hierarchical naming Has 2 parts: a hostname and a domain name.
example: information.priscilla.com
Maps names to IP addresses
11
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
DNS DETAILS
Client/server modelClient is configured with the IP
address of a DNS server Manually or DHCP can provide the
addressDNS resolver software on the
client machine sends a query to the DNS server. Client may ask for recursive lookup.
13
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
DNS RECURSION
A DNS server may offer recursion, which allows the server to ask other servers Each server is configured with the IP address of
one or more root DNS servers.
When a DNS server receives a response from another server, it replies to the resolver client software. The server also caches the information for future requests. The network administrator of the authoritative
DNS server for a name defines the length of time that a non-authoritative server may cache information. 14
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
SUMMARY
Use a systematic, structured, top-down approach to addressing and naming
Assign addresses in a hierarchical fashion Distribute authority for addressing and
naming where appropriate IPv6 looms in our future
15
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3
REVIEW QUESTIONS
Why is it important to use a structured model for addressing and naming?
When is it appropriate to use IP private addressing versus public addressing?
When is it appropriate to use static versus dynamic addressing?
What are some approaches to upgrading to IPv6?
16
Revise
d se
m2
20
13
-20
14
-AA
B-2
01
3