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New Member

routing question...

Alright, this is going to sound really stupid but I've just overconfused myself.

Here is a little background info.

I have a cisco 3560G

We currently have a 10.1.2.0 255.255.255.0 subnet

All workstations are on VLAN10 as well as anything on the 10.1.2.0 network.

If i want to start IPing some machines as 10.1.3.0 what do I need to do?  We have other machines on the same network as 10.1.5.0 and so on but those sites are connected with routers so it knows where to put the information...

can i add a secondary IP to vlan 10 so I can give a machine on 10.1.3.0 a correct gateway?  (assuming i do the configuration on the 3560G) or do I just add a secondary IP to the 3560 itself and use that as the gateway?

I know it's a bad idea to do this but i'm just curious as to how to make this work...i believe my issue is i don't have a gateway for a machine on 10.1.3.0 to talk to so the switch can tell it how to talk to the other networks and i'm not sure how to assign one to that switch.

10 REPLIES
Hall of Fame Super Blue

Re: routing question...

johnwhites wrote:

Alright, this is going to sound really stupid but I've just overconfused myself.

Here is a little background info.

I have a cisco 3560G

We currently have a 10.1.2.0 255.255.255.0 subnet

All workstations are on VLAN10 as well as anything on the 10.1.2.0 network.

If i want to start IPing some machines as 10.1.3.0 what do I need to do?  We have other machines on the same network as 10.1.5.0 and so on but those sites are connected with routers so it knows where to put the information...

can i add a secondary IP to vlan 10 so I can give a machine on 10.1.3.0 a correct gateway?  (assuming i do the configuration on the 3560G) or do I just add a secondary IP to the 3560 itself and use that as the gateway?

I know it's a bad idea to do this but i'm just curious as to how to make this work...i believe my issue is i don't have a gateway for a machine on 10.1.3.0 to talk to so the switch can tell it how to talk to the other networks and i'm not sure how to assign one to that switch.

John

The way to do this on a L3 switch is not by using secondary IPs but to create a separate vlan and L3 vlan interface ie.

on the 3560 switch

ip routing (in case it is not enabled)

int vlan 11

ip address 10.1.3.1 255.255.255.0

then one each port that has a device in vlan 11

int fa0/1

switchport mode access

switchport access vlan 11

then set the default-gateway of each device in vlan 11 ot 10.1.3.1

Jon

New Member

Re: routing question...

ahh, okay, so there would be no way for me to have the two subnets working properly on the same vlan with only the L3 switch?

Hall of Fame Super Blue

Re: routing question...

johnwhites wrote:

ahh, okay, so there would be no way for me to have the two subnets working properly on the same vlan with only the L3 switch?

John

Apologies if i misled you. Yes you can apply a secondary IP address under the vlan interface ie.

int vlan 10

ip address x.x.x.x x.x.x.x

ip address y.y.y.y y.y.y.y secondary

I was just saying that generally speaking on L3 switches that's not the way we tend to configure it.

Jon

New Member

Re: routing question...

ahh see that's what i thought but when i try to input that command i get an invalid input at the part where you type secondary so that's where i've been stuck...can you only do that on a router?

Hall of Fame Super Blue

Re: routing question...

johnwhites wrote:

ahh see that's what i thought but when i try to input that command i get an invalid input at the part where you type secondary so that's where i've been stuck...can you only do that on a router?

John

Some switches take it. What model switch and which IOS version are you running ?

Jon

New Member

Re: routing question...

it's 48pt WS-C3560G running 12.2(25)SEB4-IP-BASE looks like.

Hall of Fame Super Blue

Re: routing question...

johnwhites wrote:

it's 48pt WS-C3560G running 12.2(25)SEB4-IP-BASE looks like.

Well according to the command reference you should be able to add the "secondary" keyword.

So you are doing this

3560(config)# vlan 10

3560(config-if)# ip address 192.168.5.10 255.255.255.0 secondary

and it is erroring on the "secondary" keyword ?

Jon

New Member

Re: routing question...

well i actually have to do:

int vlan 10

and then

ip address 10.1.2.3 255.255.255.0

if i add secondary at the end

ip address 10.1.2.3 255.255.255.0 secondary

it errors at secondary.    ^

Re: routing question...

Hi,

according to the Command Reference Guide

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_sed/command/reference/cli1.html#wp1861936

the secondary IP address should be available for your IOS.

When you issue

ip address 10.1.2.3 255.255.255.0 ?

does your CLI offer you the "secondary" option?

As SEB means "Special and Early Deployments", I'd try to upgrade to latest IOS, though.

BR,

Milan

Hall of Fame Super Silver

Re: routing question...

John

Does Vlan 10 already exist? What happens if you assign a switch port to Vlan 10? Is anything else configured on interface vlan 10 when you attempt the secondary address configuration? If so, what is already configured?

HTH

Rick

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