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TOPIC: Classless and Classful, RIPv1 and RIPv2

Classless and Classful, RIPv1 and RIPv2 8 years 1 hour ago #28437

  • nezzy999
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Hi,

From what I know RIPv1 is a classful protocol and RIPv2 is a classless protocol.

I have become confused though as I was using RIPv1 on my 2811 router and when I input the command, show running-config it states;

<**Lots of info**>

ip classless

<**Lots of info**>

I noticed this line "ip classless", now why would this line be included in the readout? when I am using Ripv1?
I asked my tutor at uni and he was also unsure, does anyone have any ideas or theories?
Thanks
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Re: Classless and Classful, RIPv1 and RIPv2 7 years 11 months ago #28438

  • nezzy999
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After a discussion with some of my peers we have come up with the theory, that

RIPv1 is also classless as when it recieves a rip update of

172.16.0.0 on an interface which has a mask of /8 it will not apply the classful mask of /16, it will apply the /8 mask of the interface it recieved the update on?
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Re: Classless and Classful, RIPv1 and RIPv2 7 years 11 months ago #28439

  • S0lo
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It can be quite confusing at the beginning. But it eventually sinks in. ip classless has a totally different job than what RIP or RIPv2 does.

ip classless affects the way routes are searched for when a packet arrives at a router. If ip classless is not configured (using the no ip classless command) then a packet will NOT be routed using a route that has a subnet mask less than the classfull mask of the packet's destination IP. For example, a packet with a destination IP address 194.1.1.1 (Class C, /24). Will be routed by a route like 194.1.1.0/28 and will be routed by a route like 194.1.1.0/24 BUT it will not be routed by a route like 194.1.0.0/22 or by 194.0.0.0/16. Since /22 and /16 are less than the classfull mask /24 (i.e super nets).

If ip classless is configured, this restriction is released. a packet can be routed by any route regardless of the subnet mask. This is why default routes (that has a mask of /0) will never work unless you have ip classless configured. More here: www.cisco.com/en/US/tech/tk365/technolog...4823.shtml#classless

RIP and RIPv2 has no relation to this. RIP does not send subnet-masks during updates. It always assumes classful masks. RIPv2 sends subnet-masks. Thats why RIP is said to be classfull and RIPv2 is classless.

Thats as far as I know, any one, please correct me if I'm wrong.
Studying CCNP...

Ammar Muqaddas
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www.firewall.cx
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Re: Classless and Classful, RIPv1 and RIPv2 7 years 11 months ago #28446

Exactly like that Solo. You are correct.
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Re: Classless and Classful, RIPv1 and RIPv2 7 years 11 months ago #28447

  • Chojin
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.
I asked my tutor at uni and he was also unsure, does anyone have any ideas or theories?

I think they should fire your tutor, that he is not sure about RipV1 :).


Rip v1 uses Broadcast and doesn't send a subnet mask in its advertisements.

Rip v2 uses Multicast and DOES send a subnet thus makes it suitable for classless updates
CCNA / CCNP / CCNA - Security / CCIP / Prince2 / Checkpoint CCSA
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Re: Classless and Classful, RIPv1 and RIPv2 7 years 7 months ago #30059

For more info about the "ip classless" influence in the routing process of Cisco Routers, have a look at here:

www.cisco.com/en/US/tech/tk365/technolog...823.shtml#forwarding

It says that:
- It doesn't interfere with the way the routing table is built - the routing table is filled in the same way with or without this command: routing protocols supply routes with administrative distances/metrics, and the routing table chooses among them the routes with the best administrative distance/metric, to be used in the routing table
- It *does* interfere in the way the routing table is "read" to decide where to forward a packet, as explained by SOlo.
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