Cisco Noob - Layer 3 Routing / VLAN / Spanning Tree

[Neil Kirkland]

Hi All ...

I need some pointers on which commands / settings and where, I know what I want to achieve but the things I am trying seem to be 'mutually exclusive' - either that or i'm missing something - I am not a Cisco IOS expert but I know my way around a network.

Take 3 3560 switches in Layer 3 mode, there is a 'local' fibre spanning tree ring serving mulriple switches on each, each ring is it's own IP segment / VLAN. There is then a trunk between each switch on which I want to establish a load sharing / spanning tree circuit i.e.

SW1 hosts VLAN 2 via copper on fa0/1 -12, ip address 10.10.2.254

SW1 hosts VLAN 3 via a fibre spanning tree circuit on G0/1 & G0/2, dhcp 10.10.3.0/24, trunk 1 on G0/3 and trunk 2 on G0/4

SW1 hosts VLAN 10, ip address 10.10.10.1 (trunks 1 and 2 have no IP address but are members of VLAN 10)

SW2 hosts VLAN 4 via a fibre spanning tree circuit on G0/1 & G0/2, dhcp 10.10.4.0/24, trunk 1 on G0/3 and trunk 2 on G0/4

SW2 hosts VLAN 10, ip address 10.10.10.2 (trunks 1 and 2 have no IP address but are members of VLAN 10)

SW3 hosts VLAN 5 via a fibre spanning tree circuit on G0/1 & G0/2, dhcp 10.10.5.0/24, trunk 1 on G0/3 and trunk 2 on G0/4

SW3 hosts VLAN 10, ip address 10.10.10.3 (trunks 1 and 2 have no IP address but are members of VLAN 10)

SW1 G0/3 is a SMF trunk to SW2 G0/3

SW1 G0/4 is a SMF trunk to SW3 G0/3

SW2 G0/4 is a SMF trunk to SW3 G0/4

The trunks are configured as "trunk encapsulation dot1q", ip routing is  enabled.

I can get the trunks working OK - but I can't seem to get routing to work across them - if I define an interface on SW1 with an IP set in SW3 the switch complains so it can clearly see it so which command have I missed.

All VLAN's are part of the same domain, each VLAN has it's own DHCP hosted on it's hosting switch. The VLAN ip address is excluded from DHCP and is the default gateway for each VLAN.

All VLAN's must be able to reach VLAN2 (contains SQL servers and DNS, Time etc etc), the VLAN's are working, DHCP etc is all working - but I can't get anything other than VLAN 10 IP's to talk across the trunks - I've tried adding spanning-tree vlan 2,3,4,5,10 but this hasn't worked, the ip route-map shows nothing, if you show spanning-tree the trunk ports do show up as an interface for all VLAN's - and yet no traffic passes across them - show route displays nothing. I tried adding ip route 10.10.*.0 255.255.255.0 10.10.2.254 (where 10.10.2.254 is the ip address of VLAN 2) but that's done nothing.

I have tried various combinations - unsuccessful so far - I need the trunks to be not only fault tolerant but load sharing which kind of negates fixing IP's on them - or does it ?? - what am I missing ?

(switches are all running IP services IOS)

[Neil Kirkland]

Something just works ... ... not for me it doesn't ....

Thinking about it had it been necessary to disable completely this would have been a show stopper - since all the remote devices are on remote L2 boxes that are all linked by a ring of fibre currently running spanning tree ...

The server connection is only configured for "switchport mode access" - I'll have a play with mode trunk etc ...

[Jon Marshall]

Neil

Sorry, i may have confused the issue.

There is no need to change the server port configuration to a trunk. I was just trying to give a general example of what you would do if the server was configured as a trunk already. If it isn't making it a trunk will make no difference.

When you interconnect the switches with L3 then the same vlan/IP subnet cannot extend across those links.

But each and every switch should still be running STP so definitely you would not want to disable it anywhere.

Using "spanning-tree portfast" on a port does not disable STP it simply allows the port to begin forwarding immediately.

In terms of the L3 routed ports this command doesn't apply.

In terms of the the ports that connect to other switches you absolutely do not want to use either version of the portfast command.

Jon

[Neil Kirkland]

You beat me to it - I changed them to trunks and it caused all kinds of chaos ...

Switching them back to mode access and setting spanning-tree portfast .... if that doesn't work it's out with the wireshark - but that will be for later today - currently 5 past midnight here ....

[Neil Kirkland]

DHCP requests are passing correctly - this is a DHCP server issue .... so not one for Cisco boffins ... I'll post the DHCP resolution once I figure it out ... one thing for sure I've given up on using the switches to issue the IP's ...