Routing between two Cisco 3750 over iplink? 1

[lii8]

Hi!

i'm going to configure two 3750 over an ip-link. On both sides i have two class-a nets who are subnetted, and who are going to talk to each other (10.1.0.0 /16 and 10.2.0.0 /16).

Should i just set up a vlan for each net on the switches, or ad static routing?

Thanx for all replies!

 

[KiscoKid]

As you're already segmenting your network by the layer 3 component of the 3750, you don't actually need to setup VLANs which would achieve the same kind of thing anyway.

The VLAN approach is useful if there are people who span both sites who may have common access requirements and therefore could share the same VLAN assignment.

If this is not a requirement for you, go ahead and just setup the layer 3 component instead, i.e. static or some other kind of routing.

 

[ADB100]

On the 3750 you can set an interface to be a routed port and configure an IP address directly on the interface, thers is no need to create another VLAN for the link:

!switch #1
interface FastEthernet1/0/1
no switchport
ip address 10.255.255.1 255.255.255.252
!


!switch #2
interface FastEthernet1/0/1
no switchport
ip address 10.255.255.2 255.255.255.252
!


You will obviously need either a routing protocol running or static routes to get either switch to know about the remote networks.

HTH

Andy

 

[lii8]

Hi!!

Thanks for all help so far!! doesn't hold any deep knowledge on Cisco Switches so this is a great forum to get inputs, hints & tricks from network administrators.

Going with the tip from ADB100, and setting ip on the interfaces, but could you give me an example of a static routing between these two a-nets (10.1.0.0 /16 & 10.2.0.0. /16) on the 3750?

Again, thanx for all replies!

 

[ADB100]

!switch #1
ip route 10.2.0.0 255.255.0.0 10.255.255.2

!switch #2
ip route 10.1.0.0 255.255.0.0 10.255.255.1


That is assuming the subnet 10.1.0.0/16 exists on switch #1 and 10.2.0.0/16 exists on switch #2.

HTH

Andy

 

[lii8]

Maybe i didn't explain the net config to good.

On both sides of the switches i have to a-nets. The offices are connected with fiber. we are going to use two 3750 to link these two offices together, so on each switch - both a-nets are present and i want to access resources on both sides of the fiber-link within each subnett. 10.1.0.0 /16 and 10.2.0.0 /16 should not communicate with each other.

Could i use;

!switch #1
interface FastEthernet1/0/1
no switchport
ip address 10.255.255.1 255.255.255.252
!


!switch #2
interface FastEthernet1/0/1
no switchport
ip address 10.255.255.2 255.255.255.252
!


!switch #1
ip route 10.2.0.0 255.255.0.0 10.255.255.2
ip route 10.1.0.0 255.255.0.0 10.255.255.2


!switch #2
ip route 10.2.0.0 255.255.0.0 10.255.255.1
ip route 10.1.0.0 255.255.0.0 10.255.255.1

 

[ADB100]

No will just create a routing loop by doing that. I don't understand your setup - are you saying you have overlapping address space?

Andy

 

[lii8]

No - theres no overlapping address space. the two a-nets are present at both locations. we want to set up an ip link between the locations so machines on switch#1 can communicate with machines on switch#2 on the same subnett --> example machine 10.1.0.2 on switch#1 can communicate with 10.1.0.3 on switch#2.

did this help (--,) ??

thanks again for your patience.....

 

[KiscoKid]

I think I'll go back on what I said earlier and advise you deploy VLANs for each subnet instead.

I'd recommend assigning all 10.1.0.0 users to one VLAN (say VLAN2) and 10.2.0.0 users to, say, VLAN3.

You will also need to setup trunking between both 3750's to pass these 2 VLAN's between them. This will allow people on both sites to see other (if on the same IP subnet).

If, later on, you need the subnets to speak to each other, you will need to configure a layer 3 interface on both 3750's for each VLAN. You can then control who can talk to who through the use of ACL's if required.

Example configs follow:

interface FastEthernet0/5
description to PC on VLAN3
switchport access vlan 3
switchport mode access
no ip address
spanning-tree portfast


interface GigabitEthernet0/1
description To Remote 3750
switchport mode trunk
switchport trunk encapsulation dot1q
no ip address

If and when later on, you want to configure a layer 3 interface to allow each set of users to see each other, you can do the following:

interface Vlan2
description User VLAN for 10.1.0.0
ip address 10.1.0.1 255.255.0.0
interface Vlan3
description User VLAN for 10.2.0.0
ip address 10.2.0.1 255.255.0.0

Note each user PC will need to be configured with a default gateway of 10.1.0.1 for instance for this to work. Therefore use whatever default gateway that is already pre-configured on each person's PC for the switch layer 3 interface.

 

[ADB100]

OK. You want to 'span' the VLAN's over the fibre link - NOT route the IP traffic. This isn't the best way in my opinion but achievable none the less. The link must be configured as a VLAN trunk and both VLAN's must be enabled on each switch (which I assume they are already?).
Follow KiscoKid's config above, make sure the hosts know what gateway to use - if you already have internet access and a default gateway then you can either use static routes on the hosts or re-work the network setup so the 3750 is the first-hop before your internet router.

HTH

Andy