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198.162.x.x routing. RFC 1918 space.

192.168.0.0 is a class B space but when I route it I need to specify a class C, (third octet), subnet for the EIGRP routing process. E.G. 192.168.1.0. This must be done for every class C network on every router in the routing domain. Am I missing something here? Public class B space only requires you to specify the class B octets.

1 ACCEPTED SOLUTION

Accepted Solutions
Green

Re: 198.162.x.x routing. RFC 1918 space.

192.168.X.X is a Class C address.

Class B extends from 128.0.0.0 to 191.255.255.255

Class is determined (solely) from the most significant bits of the most significant octet.

Any address starting with a binary pattern of "00000001" through "01111111" is a Class A address (1-127.x.x.x)

Any address starting with a binary pattern of "10000000" through "10111111" (128-191.x.x.x) is a class B address.

Any address starting with a binary pattern of "11000000" through "11011111" (192 - 223.x.x.x) is a Class C address

Any address starting with "11100000" through "11101111" (224 - 239.x.x.x) is a Class D (usually used for multicast)

Everything left over (11110000 - 11111111) is Class E.

Mask is irrelevant for the sake of determining Class; Class is only determined by the leading bits of the leading octet.

FWIW

Scott

6 REPLIES
New Member

Re: 198.162.x.x routing. RFC 1918 space.

192.168 is a class c address:

Class A 0-127

Class B 128-191

Class C 192-223

Green

Re: 198.162.x.x routing. RFC 1918 space.

192.168.X.X is a Class C address.

Class B extends from 128.0.0.0 to 191.255.255.255

Class is determined (solely) from the most significant bits of the most significant octet.

Any address starting with a binary pattern of "00000001" through "01111111" is a Class A address (1-127.x.x.x)

Any address starting with a binary pattern of "10000000" through "10111111" (128-191.x.x.x) is a class B address.

Any address starting with a binary pattern of "11000000" through "11011111" (192 - 223.x.x.x) is a Class C address

Any address starting with "11100000" through "11101111" (224 - 239.x.x.x) is a Class D (usually used for multicast)

Everything left over (11110000 - 11111111) is Class E.

Mask is irrelevant for the sake of determining Class; Class is only determined by the leading bits of the leading octet.

FWIW

Scott

New Member

Re: 198.162.x.x routing. RFC 1918 space.

Got it. Thanks. Mask is irrelevant.

leading 0 = class A

leading 1 = class B

leading 11 = class C

leading 111 = class D

leading 1111 = class E

Info from IETF www site:

Private Address Space

The Internet Assigned Numbers Authority (IANA) has reserved the

following three blocks of the IP address space for private internets:

10.0.0.0 - 10.255.255.255 (10/8 prefix)

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

We will refer to the first block as "24-bit block", the second as

"20-bit block", and to the third as "16-bit" block. Note that (in

pre-CIDR notation) the first block is nothing but a single class A

network number, while the second block is a set of 16 contiguous

class B network numbers, and third block is a set of 256 contiguous

class C network numbers.

Gold

Re: 198.162.x.x routing. RFC 1918 space.

What do you mean when you say you're "forced to specify a class C (third octet) subnet? Do you mean that you have to specify 255.255.255.0 as the mask on your interfaces, or in EIGRP, or... ? Do you mean that when you configure "network 192.168.1.0" it nvgens as "network 192.168.0.0?"

I know you've already marked this as answered, but I don't really understand the question. :-)

:-)

Russ.W

New Member

Re: 198.162.x.x routing. RFC 1918 space.

If 192.168.1.0 was part of a class B address then you would only need the statement "network 192.168.0.0" in the routing eigrp 1 configuration area and it would route the 192.168.1.0 network. If you are using the 192.168.x.x space for your private addressing then you need to specify each class C network that you intend to route, eg. 192.168.1.0, 192.168.2.0 etc. on every routing process on every router participating in that process.

VIP Purple

Re: 198.162.x.x routing. RFC 1918 space.

Hello Bruce,

I think the confusion comes from the fact that the IANA reserverd address space has nothing to do with class A, B, or C addresses, they are just addresses:

10.0.0.0 - 10.255.255.255 (10/8 prefix)

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

does not mean class A, B, and C. The prefixes have nothing to do with the classfull masks for class A, B, and C.

By the way, adding ´network 192.168.0.0´ or any other network statement does not really ´advertise´ a network, it just defines the interfaces where EIGRP runs on...

Does that make sense ?

Regards,

GP

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