rip with classless and overlap question

Tamitorer1417 · ‎06-18-2019

Why I get overlap when I add router and on one port I add 10.0.0.10 with subnet mask 255.0.0.0 overlaps with the other port that have on it 10.1.0.11 255.255.0.0 even it is 16 bit subnet mask and that 8 ?

The second question is how I can ping on this network even I am using rip dynamic protocol with classfull IP (image included)

luis_cordova · ‎06-18-2019

Hi @Tamitorer1417 ,

Why I get overlap when I add router and on one port I add 10.0.0.10 with subnet mask 255.0.0.0 overlaps with the other port that have on it 10.1.0.11 255.255.0.0 even it is 16 bit subnet mask and that 8 ?

A: The network 10.0.0.0/8 have these parameters:

First host: 10.0.0.1

Last host: 10.255.255.254

Broadcast: 10.255.255.255

As you can see, the ip 10.1.0.11 is within the parameters of the network 10.0.0.0/8, that's why the device tells you there are overlaps.

This can be avoided if you change the network mask 10.0.0.0 from /8 to /16

The second question is how I can ping on this network even I am using rip dynamic protocol with classless IP?

A: The RIPv1 protocol included in its updates only the network address, so it used the class to indicate the mask.
In RIPv2, the network and the mask are included in the updates, so that different masks can be occupied, for example, using VLSM.

Regards

Tamitorer1417 · ‎06-18-2019

i have add /8 and /16 in the explain !!!

The second question is how I can ping on this network even I am using rip v1 with classfull IP even there is class-less segments !!1

Giuseppe Larosa · ‎06-18-2019

Hello Tamitoter1417,

network 10.1.0.0/16 is actually a subset actually a subnet of major network 10.0.0.0/8, this is the reason why the router is complaining about IP address overlapping. This is not allowed as it would create ambiguity in how to reach a IP prefix.

In other words a router needs a single L3 interface connected to an IP subnet and the router job is to perform inter networking between different IP subnets using its own interfaces to reach another router or the final destination of the packet.

In real world we use /24 or /25 prefixes.

So in your lab exercise I would encourage you to use more realistic subnet masks.

To solve your overlapping would be enough to use 10.0.0.0/16 and 10.1.0.0/16 but these are still too big for real world applications ( 65,533 hosts in the same IP subnet are simply too many to be handled).

Once IP overlapping is solved RIPv2 will provide end to end connectivity by allowing each router to advertise the known subnets to the neighbors.

Here stays the big advantage of dynamic routing protocols: they are able to auto adapt and are sort of plug and play.

Edit:

A little add about IP classless.

RIPv2 is a classless routing protocol because it carries both the prefix (subnet base address ) and the subnet mask (or prefix length that is the /n notation).

However, by default RIPv2 will use auto-summary: in advertising subnets if the outgoing interface belongs to a different major network (here we mean Class A, Class B, Class C IP addresses with Class A using 1-126 decimal in first octect , Class B 128-191 in first octect, Class C 191-223 decimal in first octet) RIPv2 auto summarizes to major network so for example a single 10.0.0.0/8 is sent to the router R0 by router R1 in IP subnet 13.1.0.0/16 so R0 does not see the details of subnets 10.0.0.0/16 and 10.1.0.0./16 but only a single entry.

This mode of working does not support discontiguos subnets of the same major network.

If for example one interface of R0 had an IP address like 10.2.0.0/16 RIPv2 would needs to be tuned using the commands

router rip

version 2

>>no auto-summary

in both R0 and R1.

In this way the exact prefixes are advertised also across different major networks as auto summarization does not happen anymore.

So R0 could advertise 10.2.0.0/16 to R1 and could know that via R1 it can reach 10.0.0.0/16 and 10.1.0.0/16 even if the common subnet between R0-R1 belongs to major network 13.0.0.0/8.

Hope to help

Giuseppe

Tamitorer1417 · ‎06-18-2019

Thank you very much but i have make mistake in explain , my question was i am using the rip v1 the class-full version but there is classless segment but even with that i can ping , why this happen sorry again ....

Jon Marshall · ‎06-18-2019

RIPv1 is a classful routing protocol but that does not mean it must use the classful mask, it just means it must use the same mask for all the subnets within a major network.

To put it simply you have used the class A networks 13.0.0.0/8 and 14.0.0.0/8 but you have applied a /16 subnet mask. This works fine even with a classful routing protocol like RIPv1 but if you use any other subnets from either 13.0.0.0/8 or 14.0.0.0/8 then you must use a /16 mask because the subnet mask is not included in routing updates.

Jon

Tamitorer1417 · ‎06-18-2019

Thank you very much

@Jon Marshall wrote:

RIPv1 is a classful routing protocol but that does not mean it must use the classful mask, it just means it must use the same mask for all the subnets within a major network.

To put it simply you have used the class A networks 13.0.0.0/8 and 14.0.0.0/8 but you have applied a /16 subnet mask. This works fine even with a classful routing protocol like RIPv1 but if you use any other subnets from either 13.0.0.0/8 or 14.0.0.0/8 then you must use a /16 mask because the subnet mask is not included in routing updates.

Jon

As i understand from you that mean if i use instead then 10.0.0.0/8 if i used 14.1.1.0/24 with the 13.1.0.0/16 and 14.1.0.0/16 this example will case a problem ? and the overlapping happen in the first question because 10.1.0.0/16 is subnet from 10.0.0.0/8 and they cannot be together as the subnet must be under the main network id ????

Jon Marshall · ‎06-18-2019

You can use different subnet masks for different major networks and it will work but you must use the same subnet mask within the same major network so 14.1.0.0/16 and 14.2.0.0/16 would work but 14.1.0.0/16 and 14.1.1.0/24 would not work and would cause problems.

Jon