Connecting two Cisco 2950 switches to a 2600 router

[velkropie]

Hello,

I'm trying to have two LANs connected to 2950 switch each, connect to a 2600 router and have the two LANs communicate with each other...i can't seem to get it working...any help...thanks

LAN 1 192.168.10.1/20

LAN 2 192.168.12.1/21

Thanks again

[pkhatri]

Could you post the relevant bits of config you have used ?

Paresh

[jkout]

Well, for one thing, your subnets overlap. The 192.168.10.1/20 subnet includes the 192.168.12.1/21 subnet. When a host on the 192.168.10.1/20 network is trying to talk to a host on the 192.168.12.1/21 network, it appears to the host as though the destination is on the same subnet, so the traffic never gets sent to the 2600.

Use networks that don't overlap and you'll have better luck.

IP Address : 192.168.10.1

Network ID : 192.168.10.0

Broadcast ID : 192.168.15.255

Subnet Mask : 255.255.240.0

Subnet Bits : 20

Host Bits : 12

Hosts per Subnet : 4094

[velkropie]

ok, thanks

does the broadcast or the subnet address become the default gateway?

[pkhatri]

Since you are using a router for inter-vlan routing, the IP address of the interface on the router will be the default gateway that you configure on your hosts/PCs.

Hope that helps - pls rate the post if it does.

Paresh

[jkout]

Hey, I made a mistake in my last post. The network ID for the 192.168.10.1/20 network is actually 192.168.0.0. The broadcast ID is still 192.168.15.255. But, you can still have the router interface for this LAN be 192.168.10.1, if you need to.

interface FastEthernet0/0

ip address 192.168.10.1 255.255.240.0

! this is a /20 subnet

! Network ID = 192.168.0.0

! Usable IPs = 192.168.0.1 - 192.168.15.254

! Braodcast ID = 192.168.15.255

interface FastEthernet0/1

ip address 192.168.16.1 255.255.248.0

! this is the next available /21 subnet

! Network ID = 192.168.16.0

! Usable IPs = 192.168.16.1 - 192.168.23.254

! Braodcast ID = 192.168.23.255

The gateway for any client on 192.168.0.1 - 192.168.15.254 would be 192.168.10.1 (of course, you can't have a client use 192.168.10.1, because that's the IP address of the router interface). The gateway for any client on 192.168.16.2 - 192.168.23.254 would be 192.168.16.1.

I would actually recommend using a smaller subnet for both LANs, unless you really need 4094 clients on one and 2046 on the other. Those are pretty big subnets (ie: broadcast domains) and if you have that many clients, you should consider breaking them into smaller subnets, say 16 different /24 subnets.

[velkropie]

ok, thanks

i have decided to use this subnet mask

network address:192.168.10.0

subnet: 255.255.255.192

this will give me two subnets with 62 hosts each which will be fine..

if my subnets are 64 and 128

first host are 65 and 129 each subnet

last host are 126 and 190 each subnet

the broadcast addresses are 127 and 191...

what ip addres do i use for each default gateway when i set the hosts and switches? this is what's killing me right now...

also, do i have to set the ports on each switch that connect to the router as the default gateway as well as the routers fa0/0 and fa0/1?

thanks for your help

[jkout]

Alright, these are only basic configs here:

Router

!*******************************************

hostname Router

int fastethernet0/0

description Network 1

ipaddress 192.168.10.65 255.255.255.192

int fastethernet0/1

description Network 2

ip address 192.168.10.129 255.255.255.192

end

!*******************************************

Switch 1 (the one connecting to f0/0)

!*******************************************

hostname SwitchNet1

int f0/1

description Host 1 Net 1

no ip address

no shut

!

int f0/2

description Host 2 Net 1

no ip address

no shut

!

int f0/3

description Host 3 Net 1

no ip address

no shut

!

int f0/4

description Host 4 Net 1

no ip address

no shut

!

int range f0/5 - 23

no description

no ip address

shut

int f0/24

description UPLINK to Router

no ip address

no shut

!

int vlan 1

ip address 192.168.10.66 255.255.255.192

no shut

!

default-gateway 192.168.10.1

end

!*******************************************

Switch 2 (the one connecting to f0/1)

!*******************************************

hostname SwitchNet2

int f0/1

description Host 1 Net 2

no ip address

no shut

!

int f0/2

description Host 2 Net 2

no ip address

no shut

!

int f0/3

description Host 3 Net 2

no ip address

no shut

!

int f0/4

description Host 4 Net 2

no ip address

no shut

!

int range f0/5 - 23

no description

no ip address

shut

int f0/24

description UPLINK to Router

no ip address

no shut

!

int vlan 1

ip address 192.168.10.130 255.255.255.192

no shut

!

default-gateway 192.168.10.129

end

!*******************************************

This config assumes only ports f0/1 - f0/4 will be used on each switch. If that is not the case, you will need to modify the interface configs accordingly. You may want to use descriptions more suited than to your network on the switchports. Also, this config assumes the router is connected to port f0/24 on each switch as well.

The default-gateway for the hosts and the switches is going to be the router IP address for the subnet they are attached to. The hosts/switches attached to f0/0 use 192.168.10.65 as their gateway. The hosts/switches attached to f0/1 use 192.168.10.129 as their gateway.

You do not need to configure a port on the switch as the default-gateway. The default-gateway is an IP address the host/switch uses to direct all traffic from itself out past the router. In fact, if you don't need the switch to talk to devices on the other subnet, you don't even need to configure a default-gateway on the switches (but I would anyway).

[velkropie]

ok, thanks

one question...why did you set the default-gateway of the 192.168.10.65 net to 192.168.10.1?

didn't it have to be 192.168.10.65...like the .129 one?

Thanks

[jkout · Accepted solution]

Yes, that was a typo. It should be 192.168.10.65.