ospf version 2

Ok,
I have a primary address of 10.31.3.1/25 on a fast Ethernet interface. I also have a secondary address of 22.6.21.1/24 on that same exact interface. The primary address has an ospf statement putting it in the backbone (area 0). Now I want to make my secondary ip address talk to my other networks via ospf in area 8, but I just learned the hard way that you can't have a secondary IP address talk via ospf unless you are using version 2. So now I am a bit confused how to properly configure my secondary interface with version 2. Anybody got any input?

Cheers’!

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Comments

EdTheLad

I dont know where you came up with the version 2 idea, as the current standard everyone is using for ipv4 is ospf v2.I think your problem comes down to the area command.You cannot config a secondary ip address to belong to a different area than the primary,this must both be in the same area.This is a rule in ospf regarding secondary interfaces.

malweth

Since you're using FastEthernet and going between routers (probably), you could dot1q tunnel the two addresses as a work-around. Might not work well if you have other things connected to that FE line...

tech-airman

happy420golucky wrote:

Ok,
I have a primary address of 10.31.3.1/25 on a fast Ethernet interface. I also have a secondary address of 22.6.21.1/24 on that same exact interface. The primary address has an ospf statement putting it in the backbone (area 0). Now I want to make my secondary ip address talk to my other networks via ospf in area 8, but I just learned the hard way that you can't have a secondary IP address talk via ospf unless you are using version 2. So now I am a bit confused how to properly configure my secondary interface with version 2. Anybody got any input? Cheers’!

happy420golucky,

According to "RFC 1918 - Address Allocation for Private Internets", it states "Because private addresses have no global meaning, routing information about private networks shall not be propagated on inter-enterprise links, and packets with private source or destination addresses should not be forwarded across such links." RFC 1918 also states ...

3. 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)

So your primary interface IP address falls within a valid private IP address range but your secondary interface IP address does not. So the problem you're facing may be enforcement of RFC 1918 within the IOS.

Source:

RFC 1918 - Address Allocation for Private Internets - http://www.ietf.org/rfc/rfc1918.txt

Ciscopimpenator

Tech Airman,

I think he is just building a home lab so using 10.0.0.0 /8 will work.

You can use any of the RFC 1918 addresses inside your private network. Have you gotten to that point in the CCNA academy yet?

Real world example....Go purchase a Linksys home router and see what network they use for management....192.168.1.0 /24 which is covered in RFC 1918

-Ciscopimpenator

tech-airman

Ciscopimpenator wrote:

Tech Airman,

I think he is just building a home lab so using 10.0.0.0 /8 will work.

You can use any of the RFC 1918 addresses inside your private network. Have you gotten to that point in the CCNA academy yet?

Real world example....Go purchase a Linksys home router and see what network they use for management....192.168.1.0 /24 which is covered in RFC 1918

-Ciscopimpenator

Ciscopimpenator,

happy420golucky stated "I also have a secondary address of 22.6.21.1/24 on that same exact interface." The IP address of "22.6.21.1" falls outside of the private IP range of 10.0.0.0 ~ 10.255.255.255 as permitted by RFC 1918 therefore it is a public IP address. RFC 1918 states "...,routing information about private networks shall not be propagated on inter-enterprise links, and packets with private source or destination addresses should not be forwarded across such links..." happy420golucky stated "Now I want to make my secondary ip address talk to my other networks via ospf in area 8,..." That suggests that happy420golucky is trying to configure this router as an ABR between areas 0 and 8. RFC 1918 specifically states "...and packets with private source or destination addresses should not be forwarded across such links." That is why RFC 1918 may prohibit private IP to public IP routing , in this case between the private IP subnet of 10.31.3.0 subnetwork to the public IP subnet of 22.6.21.0 subnetwork. Apparently, happy420golucky is trying to accomplish routing between his 10.31.3.0 subnetwork with the 22.6.21.0 subnetwork because happy420golucky said "Now I want to make my secondary ip address talk to my other networks via ospf in area 8,..."

One method to be in compliance with RFC 1918 would be NAT. That way, the private source IP address in the IP header of the packet will be substituted with a valid public source IP address. Then the packet can be routed around the Internet because it would no longer have the private source IP address in the IP header of the packet. However, since this router seems to have a single interface with a secondary ip address, I don't think NAT would be a feasible. NAT would not be feasible because the FastEthernet interface would need to be designated either "ip nat inside" or "ip nat outside" not both.

I have graduated Semester 4 of the Cisco Networking Academy Program so I have passed that point that you're referring to. I also am currently using a Linksys BEFSR41 router as my outer router so I know that it is in compliance with RFC 1918 because I'm typing this reply through it.

EdTheLad

Tech-Airman i find it too funny that you are applying the ip address allocation rules to a home lab.
RFC 1918 defines the rules of address allocation on the internet, it does not relate to our fantasy lab ip address assignment.

Humper

RFC 1918 -- Is a document outlining the private address block, and making rules about how it should be used.

Technically you could put a RFC 1918 address out into the internet if ISP's were not denying the private address blocks.

This is a big misconception! You can use the private address space anywhere! Its just an IP block!

darkuser

hmmm ... so you eol'd the modem ????

happy420golucky

Sorry for the late reply on this. I just got back from doing a site survey.
Anyways, I was obviously had a misconception about ospfv2. *Lesson learned (don't listen to somebody unless you look it up yourself)

From what I understand is that ospfv2 is already on my IOS images that I am currently using. So I put that secondary ip address in area 0 with the primary address. I was then able to access my servers, dns, etc. I honestly didn't remember that rule that Ed stated, but won't ever forget I tell ya.

The interface that I was having an issue with doesnt connect to the internet, but simply a private network that I have setup here. So like I said, it was a misunderstanding on my part. Thanks for you input guys!