C HAPTER 6 Part 2 1 Revised sem AAB-2013

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 sem AAB-2013

S UPERNETTING / EXAMPLE OF ROUTE SUMMARIZATION The network administrator assigned network numbers through to networks in a branch office. 3 Revised sem AAB Branch-Office Networks Enterprise Core Network Branch-Office Router

C ONTINUE.. The branch office can summarize its local network numbers and report that it can reach /14. By advertising this single route, the router is saying” route packets to me if the destinations has the first 14 bits set to the first 14 bits are equal to Revised sem AAB-2013

/14 S UMMARIZATION Second Octet in Decimal Second Octet in Binary Revised sem AAB-2013 the leftmost 6 bits from 16  19 are identical.

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 sem AAB-2013

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 sem AAB-2013

E XAMPLE The following network numbers are defined at branch office. Can they be summarized? Revised sem AAB-2013

D ISCONTIGUOUS SUBNETS based on the above figure, both routers cannot reach remote subnets of network since there are not connected. solve it suing CIDR – a classless routing protocol. Router A advertises that it can get to network /20. Router B advertises that it can get to network /20 CIDR understand prefixes of any length, the routers can route to DS. 9 Revised sem AAB-2013

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 sem AAB-2013

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 sem AAB-2013

C ONTINUE.. 12 Revised sem AAB-2013

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 sem AAB-2013

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 sem AAB-2013

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 sem AAB-2013

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 sem AAB-2013