Sunday, September 13, 2009

CCNA2 Chapter 5 - 6 note

Finish another 2 chapters.

My note

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Chapter 5 RIPv1

RIP messages are encapsulated in a UDP segment, with source and destination ports of 520.

One RIP update can contain up to 25 route entries. The maximum datagram size is 512 bytes, not including the IP or UDP headers.

To enter the router configuration mode for RIP, enter 'router rip' at the global configuration prompt.

debug ip rip
undebug all

The correct solution is to use the passive-interface command, which prevents the transmission of routing updates through a router interface but still allows that network to be advertised to other routers. Enter the passive-interface command in router configuration mode.

Router(config-router)#passive-interface interface-type interface-number

This command stops routing updates out the specified interface. However, the network that the specified interface belongs to will still be advertised in routing updates that are sent out other interfaces.

RIP is a classful routing protocol that automatically summarizes classful networks across major network boundaries

classless routing protocols like RIPv2 allow the same major (classful) network to use different subnet masks on different subnets, better known as Variable Length Subnet Masking (VLSM).

How does R2 know that this subnet has a /24 (255.255.255.0) subnet mask?
R2 uses its own subnet mask on this interface and applies it to this and all other 172.30.0.0 subnets that it receives on this interface

RIPv1 lack of support for discontiguous networks. It may make load balancing between 2 discontinous network

'default-information originate' - specify that this router is to originate default information, by propagating the static default route in RIP updates.

you can see that there is a candidate default route, as denoted by the R* code. The static default route on R2 has been propagated to R1 in a RIP update. R1 has connectivity to the LAN on R3 and any destination on the Internet.

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Chapter 6 VLSM

CIDR uses Variable Length Subnet Masks (VLSM) to allocate IP addresses to subnets according to individual need rather than by class.

As you most likely recall, VLSM is simply subnetting a subnet. VLSM can be thought of as sub-subnetting.

As you previously learned, route summarization also known as route aggregation, is the process of advertising a contiguous set of addresses as a single address with a less-specific, shorter subnet mask. Remember that CIDR is a form of route summarization and is synonymous with the term supernetting.

CIDR allows for supernetting. A supernet is a group of major network addresses summarized as a single network address with a mask less than that of the default classful mask.

Supernetting refers to the ability to sumarise networks less than the classfull default mask.

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