1. C HAPTER 6 Part 2 1 Revised sem2 2013-2014 -AAB-2013

2. R OUTE SUMMARIZATION (A GGREGATION ) 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 Revised sem2 2013-2014 -AAB-2013

3. S UPERNETTING / 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 Revised sem2 2013-2014 -AAB-2013 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

4. C ONTINUE.. 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 Revised sem2 2013-2014 -AAB-2013

5. 172.16.0.0/14 S UMMARIZATION Second Octet in Decimal Second Octet in Binary 16 000100 00 17 000100 01 18 000100 10 19 000100 11 5 Revised sem2 2013-2014 -AAB-2013 the leftmost 6 bits from 16  19 are identical.

6. R OUTE 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 Revised sem2 2013-2014 -AAB-2013

7. C ONTINUE.. 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 Revised sem2 2013-2014 -AAB-2013

8. E XAMPLE 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 Revised sem2 2013-2014 -AAB-2013

9. D ISCONTIGUOUS 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 Revised sem2 2013-2014 -AAB-2013

10. G UIDELINES FOR A SSIGNING N AMES Names should be Short Meaningful Unambiguous Distinct Case insensitive Avoid names with unusual characters Hyphens, underscores, asterisks, and so on 10 Revised sem2 2013-2014 -AAB-2013

11. D OMAIN N AME S YSTEM (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 Revised sem2 2013-2014 -AAB-2013

12. C ONTINUE.. 12 Revised sem2 2013-2014 -AAB-2013

13. DNS D ETAILS Client/server model Client is configured with the IP address of a DNS server Manually or DHCP can provide the address DNS resolver software on the client machine sends a query to the DNS server. Client may ask for recursive lookup. 13 Revised sem2 2013-2014 -AAB-2013

14. DNS R ECURSION 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 Revised sem2 2013-2014 -AAB-2013

15. S UMMARY 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 Revised sem2 2013-2014 -AAB-2013

16. R EVIEW Q UESTIONS 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 Revised sem2 2013-2014 -AAB-2013