IP Address Help

skullknight10

In a bit of a pickle here. I can't figure out what I'm doing wrong for changing the IP address of the following example....

LAX s0/1/1 and SFO s0/1/0 both need to be up status together. When I start, 10.0.0.69/30 for SFO is already preset, assigned but shown as down status. It wants me get SFO to up status and change the IP address for LAX s0/1/1 with a 10.0.0.68/30, as well as show being up status. Well what happens is if I enter the 10.0.0.68/30 IP for LAX the 10.0.0.69/30 will be gone and says unassigned. I keep on failing because I can't get both IP's to be up at the same time. Below are the 2 IP addresses with the bold one on bottom as the one I need to change. I really hope this makes sense. If not I could attach some pics I suppose.

10.0.0.69/30 SFO
10.0.0.68/30 LAX

shortstop20

You cannot(nor should you) assign two IP addresses within the same subnet to interfaces on the same router.

skullknight10

shortstop20 wrote: »

You cannot(nor should you) assign two IP addresses within the same subnet to interfaces on the same router.

Ok well then what do I do if 10.0.0.69/30 if already given as SFO and I'm told "addresses on 10.0.0.68/30 network are used for serial connection"?

TWX

10.0.0.68 is a network address in a /30 network. It will not work properly this way. 10.0.0.68 would be the network, 10.0.0.69 and .70 would be two hosts, and 10.0.0.71 would be the broadcast address.

dtakhar

yup, you can't assign the network address, if its a /30 for the subnet that means you got 2 ips, so .69 and .70 would be fine.

you will typically see /30 for serial wan links to conserver ip address, as you only need 1 ip on each side of the interface for a wan connection.

TWX

It's even possible with Cisco equipment to use /31 addresses on point-to-point links like router-to-router, but the use of that method is not part of the CCNA curriculum. It uses IP in a way different than it was originally conceived as I understand, so that's probably why they don't get into it.

shortstop20

TWX wrote: »

10.0.0.68 is a network address in a /30 network. It will not work properly this way. 10.0.0.68 would be the network, 10.0.0.69 and .70 would be two hosts, and 10.0.0.71 would be the broadcast address.

I think he's trying to assign these IPs on the same router though. Maybe not, that's just how I took his original post.

OP, to clarify, you cannot have two IPs in the same subnet on one router. If you are not doing that, then disregard.

You should use .69 and .70 as TWX pointed out.

skullknight10

shortstop20 wrote: »

I think he's trying to assign these IPs on the same router though.

Yes you are correct, the same router. Sorry I didn't clarify that. I see all of you pretty much say you cannot use/be on the same subnet. Well that contradicts what my instructions are. This is why I'm so confused and have to come to the forums for some help. I feel like my head is spinning. Below are my given instructions to be able to complete this.

"Change the IP address for the LAX s0/1/1 interface. SFO s0/1/0 is already assigned as 10.0.69/30. Addresses on the 10.0.0.68/30 network are used for the serial connection. Both interfaces should be assigned an IP address. Both interfaces should be using the same subnet mask. The IP address assigned to both interfaces should be on the same subnet."

shortstop20

skullknight10 wrote: »

Yes you are correct, the same router. Sorry I didn't clarify that. I see all of you pretty much say you cannot use/be on the same subnet. Well that contradicts what my instructions are. This is why I'm so confused and have to come to the forums for some help. I feel like my head is spinning. Below are my given instructions to be able to complete this.

"Change the IP address for the LAX s0/1/1 interface. SFO s0/1/0 is already assigned as 10.0.69/30. Addresses on the 10.0.0.68/30 network are used for the serial connection. Both interfaces should be assigned an IP address. Both interfaces should be using the same subnet mask. The IP address assigned to both interfaces should be on the same subnet."

Is this in a lab manual or has your teacher assigned this to you?

Most Cisco routers will not only reject two interfaces with IP addresses in the same subnet, they will also give you an error message stating that it is rejected. In the case of your router, it's simply rejecting it but not stating the reason why.

Two interfaces on a router should never have IPs in the same subnet because it would cause an identical routing statement to appear on two interfaces.

Can you provide a screenshot of the network, with IP addresses?

skullknight10

shortstop20 wrote: »

Is this in a lab manual or has your teacher assigned this to you?

Most Cisco routers will not only reject two interfaces with IP addresses in the same subnet, they will also give you an error message stating that it is rejected. In the case of your router, it's simply rejecting it but not stating the reason why.

Two interfaces on a router should never have IPs in the same subnet because it would cause an identical routing statement to appear on two interfaces.

Can you provide a screenshot of the network, with IP addresses?

This is a lab. Attached is a screenshot of what I need to do. As you can see I'm fine on encapsulation and no shutdown status. IP part is just throwing me through a loop. As I stated SFO s0/1/0 is preset at 10.0.0.69/30 255.255.255.252. The instructions when you open the Lab state "Addresses on the 10.0.0.68/30 network are used for the serial connection" which I also mentionedin the last post.

Yanio

The instructions seem to suggest that we're dealing with two routers, not one. Item 6 specifically mentions 'both' routers.

So I assume SFO s0/1/0 is connected to LAX s0/1/1. As mentioned by TWX and Shortstop20 above 10.0.0.68/30 has two usable IP addresses, 10.0.0.69 & 10.0.0.70. As the 69 (i'm such a child) address is used, that only leave you with 10.0.0.70 255.255.255.252 for the LAX s0/1/1 interface.

HTH!

shortstop20

Yanio wrote: »

The instructions seem to suggest that we're dealing with two routers, not one. Item 6 specifically mentions 'both' routers.

So I assume SFO s0/1/0 is connected to LAX s0/1/1. As mentioned by TWX and Shortstop20 above 10.0.0.68/30 has two usable IP addresses, 10.0.0.69 & 10.0.0.70. As the 69 (i'm such a child) address is used, that only leave you with 10.0.0.70 255.255.255.252 for the LAX s0/1/1 interface.

HTH!

What he said.