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Combining two Networks into one - How?

Hi Guys, I am bit lost here. Please have a look at the attached network topology. I need to combine 172.20.68.0 into 172.24.46.0 so only one default gateway (172.24.46.2) is present. So in the final version of the network there won't be any 172.20.68.0 network.

As Cisco 3650 172.20.68.1 is connected to 172.24.46.13 via Fa22, how can you configure 172.20.68.1 so the vlan 429 be on the same subnet as 172.24.46.0 ? Does these two switches need to be connected as bridge?

what if I change the vlan IP to 172.24.46.3 so that all ports on vlan 426 would have 172.24.46.0 network address. Does that mean that this new vlan 426 would be on the same broadcast domain as the existing network 172.24.46.0 is? All I want is to have same network address 172.24.46.0 for the two 172.20.68.0 and 172.24.46.0 networks.

Any help would be appreciated. Thanks.

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Accepted Solutions
Hall of Fame Super Silver

Re: Combining two Networks into one - How?

Hello Shawkat,

if you reach any IP subnet in 172.20.x.x range via an IP next-hop that is in 172.20.68.0/24 you cannot remove this IP subnet !

All the suggestions and from your request lead to think that subnet 172.20.68.0/24 was a leaf without no other network behind it.

If it is not so I would do the following:

just move users from vlan428 to vlan1 and let in vlan428 the ports needed to reach the ip next-hops used to reach other subnets in range 172.20.x.x.

If the only subnet is 172.20.68.0/24 without any IP subnet behind you can go on moving to vlan 1 the ports on RB.

Vlan1 is not recommended for use for end users, It would be better to use a different vlan number.

Hope to help

Giuseppe

11 REPLIES

Re: Combining two Networks into one - How?

Hi!

Sorry but from your network I do not understand where are your networks located. On the drawing topology it appear no clue about your subnets.

Second: you cannot put 2 separate networks through one gateway (172.20.68.0 will not accept 172.24.46.2 as gw).

Third: "Cisco 3650 172.20.68.1 is connected to 172.24.46.13 via Fa22" you have a L1 link (FA22) connecting 2 different subnets? How do you reach the other subnet?

Combining 2 networks in one means usually summarize of subnets, but it will not work in your case because your subnets are not from the same range.

Maybe some NAT can solve your problem, but since I do not understand your explanation and drawing I cannot say that this will fit.

Good luck!

Cheers,

Calin

Re: Combining two Networks into one - How?

I agree with Calin. We don't know where your IPs are in your diagram. If they are all on the same switch, you could use intervlan routing, but you need a layer 3 switch for that, or create vlans in your router.

Sorry to not be able to help further.

--John

HTH, John *** Please rate all useful posts ***
Community Member

Re: Combining two Networks into one - How?

Thank you guys for your feedbacks. Sorry for not clarifying the drawing properly.

Cisco Router(172.20.68.1) has the 172.20.68.0 subnet and vlan 429 is that subment.

Cisco Router(172.24.46.13) has the 172.24.46.0 subnet.

Cisco 3650 172.20.68.1 is connected to 172.24.46.13 via Fa22 of 172.20.68.1 ("no switchport" on this interface)

I would like to change the 172.20.68.0 to 172.24.46.0 with keeping the same topology. My goal is to use one gateway(172.24.46.2) instead of two. So gateway 172.20.68.21 is not required.

Hope I make sense. Appreciate your inputs.

Hall of Fame Super Silver

Re: Combining two Networks into one - How?

Hello,

I agree with collegues that your picture provides no info.

However :

>> As Cisco 3650 172.20.68.1 is connected to 172.24.46.13 via Fa22, how can you configure 172.20.68.1 so the vlan 429 be on the same subnet as 172.24.46.0 ? Does these two switches need to be connected as bridge?

yes, the simplest solution is:

C3560:fas0/22 access port in vlan 429 connects to switch2 port 0/x access-port in vlan Y.

So you have joined the two broadcast domains and then you can change SVI vlan y ip address in 172.24.46.3.

Other suggestion:

because both ip subnets are in RFC 1918 you can simply use a routing protocol to make the two networks to communicate.

Hope to help

Giuseppe

Community Member

Re: Combining two Networks into one - How?

Hi giustar, Thanks for your input.

>>C3560:fas0/22 access port in vlan 429 connects to switch2 port 0/x access-port in vlan Y.

So you have joined the two broadcast domains and then you can change SVI vlan y ip address in 172.24.46.3.

Two broadcast domains are connected via fa0/22 ('no switchport' on this port). I would like to have one single 172.24.46.0 network instead of having 172.20.68.0 as well. Any ways to do that. I don't wanna route two networks, instead I would like to use one network.

Hall of Fame Super Silver

Re: Combining two Networks into one - How?

Hello Shawkat,

if fas0/22 is currently a routed port "no switchport " makes it a switchport

int fas0/22

switchport

switchport mode access

switchport access vlan 429

on the other side

int fas0/x

switchport

switchport mode access

switchport access vlan y

and you have joined the two broadcast domains I used this and works.

Hope to help

Giuseppe

Community Member

Re: Combining two Networks into one - How?

Giuesppe, Thanks heaps for your suggestion. If I follow your steps, does that mean that vlan 429 IP address can be changed to vlan y address?

If I make vlan 429 as access vlan , will it be able to communicate with vlan y on another switch?

Hall of Fame Super Silver

Re: Combining two Networks into one - How?

Hello Shawkat,

yes as explained in previuos post this a trick.

Another solution could be that of extending the right vlan on the switch and change configuration of ports so that they become members of the right vlan y

because you want to use a single ip subnet there is an impact for users that need to change their ip address so you can also move their ports to vlan y.

This is a cleaner solution.

In this case you can use a trunk link between the two switches to carry vlan y and assign the ports that were in vlan 429 to vlan y.

SVI vlan 429 in this last scenario plays no role and is useless you can create an SVI vlan y if needed.

Hope to help

Giuseppe

Community Member

Re: Combining two Networks into one - How?

Finally I am about to do this. To avoid any outage or confusion, I would like to check with you guys first.

Router A: VLAN1 172.24.46.0/24

Router B: VLAN428 172.20.68.0/24

Router A is connected to Router B port 22 via Layer 3 link ("no switchport")

To extend Router A VLAN 1 on Router B, I am making port 22 as accessport of VLAN1. This will make the link as layer 2 between two switches.

Router B is routed to 172.20.x.x.(via another port) So my question, if after the changes, would both rotuer still be able to route traffic to 172.20.x.x?

Thanks in advance

Hall of Fame Super Silver

Re: Combining two Networks into one - How?

Hello Shawkat,

if you reach any IP subnet in 172.20.x.x range via an IP next-hop that is in 172.20.68.0/24 you cannot remove this IP subnet !

All the suggestions and from your request lead to think that subnet 172.20.68.0/24 was a leaf without no other network behind it.

If it is not so I would do the following:

just move users from vlan428 to vlan1 and let in vlan428 the ports needed to reach the ip next-hops used to reach other subnets in range 172.20.x.x.

If the only subnet is 172.20.68.0/24 without any IP subnet behind you can go on moving to vlan 1 the ports on RB.

Vlan1 is not recommended for use for end users, It would be better to use a different vlan number.

Hope to help

Giuseppe

Community Member

Re: Combining two Networks into one - How?

This one worked!

I kept the VLAN429 and changed its ip to 172.24.46.x and made the port 22 as access port of VLAN 429. Everything is working perfect!

Thanks for your time and assistance :-)

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