enabling IP routing in a production SW

[garyrivers]

i installed a 3560 and like an idiot in forgot to enable ip routing!!  So now i need to enable ip routing and enable eigrp.

my question is:  what should i when i enable those two?

Thanks

[Jon Marshall]

garyrivers wrote:
i installed a 3560 and like an idiot in forgot to enable ip routing!!  So now i need to enable ip routing and enable eigrp.
my question is:  what should i when i enable those two?
Thanks

Gary

Not sure i understand. If the 3560 needs to route and run EIGRP then how is the network working correctly now ? Presumably you are routing the vlan(s) off something else ?

Are you asking how to enable it or what will happen when you do and when you should do it ?

Without understanding what it is meant to route and just as importantly what is doing that routing now it's difficult to answer.

Jon

[garyrivers]

Jon, i screwed up my question:

when i enable ip routing and eigrp the SW goes from a L2 to a L3 SW.  And when it goes to a L3 and ip routing, etc are enabled will the SW learn dynamic and static routes that are on our LAN?

and durign the learning process will the network go down?

Thanks guys!

[Jon Marshall]

garyrivers wrote:
Jon, i screwed up my question:
when i enable ip routing and eigrp the SW goes from a L2 to a L3 SW.  And when it goes to a L3 and ip routing, etc are enabled will the SW learn dynamic and static routes that are on our LAN?
and durign the learning process will the network go down?
Thanks guys!

Gary

Again it comes down to how the routing is working at the moment and how you are routing things. So for example if you have multiple vlans on your 3560 that are being routed off another device and you enable ip routing and eigrp on the 3560 that should not affect the clients in the vlans because their default-gateway hasn't changed and the 3560 still has it's mac-address table.

Your access to the switch may well be affected though if you are logged on remotely as you need to change the ip default-gateway (if you have set one) to a default-route when you enable ip routing. If you are logged onto the switch at the console simply remove the default-gateway, enable ip routing and add the default-route.

The network should not go down but i am wary of saying for sure because i still don't understand what the 3560 will be routing for ? ie. if the 3560 isn't routing at the moment then all devices connected to this switch must be routing off something else. So why do you need to enable ip routing, what are you trying to achieve ?

Jon

[garyrivers]

Jon, right now it's an L2 SW so all traffic is running on the same VLAN.  so all devices on the main VLAN have the same Default gateway.

i have a RTR that's acting as the default gateway.

what i'm trying to is set it up so that i can get off the RTR and have this SW as the GW.

i've attached a .png file for reference.

[Jon Marshall]

garyrivers wrote:
Jon, right now it's an L2 SW so all traffic is running on the same VLAN.  so all devices on the main VLAN have the same Default gateway.
i have a RTR that's acting as the default gateway.
what i'm trying to is set it up so that i can get off the RTR and have this SW as the GW.
i've attached a .png file for reference.

Well, until you change the default-gateway of the clients nothing should happen. As a previous poster mentioned you will need IP services to run the full version of EIGRP. When you enable ip routing and eigrp all that should happen is the 3560 will form a neighborship with the router and exchange routes. The clients in the vlan will still send traffic to the router for their default-gateway.

To have the clients route off the 3560 you will then need to either -

1) move the IP address from the router to the L3 vlan interface you create on the switch for the client vlan. Bear in mind arp tables here, especially on the clients as they will still be pointing to the mac-address for the router interface and not the vlan interface on the 3560

or

2) assign a different IP address to the L3 SVI and then update the DHCP default-gateway (assuming you are using DHCP). Again you are then still dependant on the client timing information out, this time rather than an arp entry, you have to wait until the client renews it's lease, or do an ipconfig /release, ipconfig /renew on each client.

So enabling the 3560 to route and run EIGRP is not really the issue, it is more to do with the clients then routing off the 3560. With this sort of thing we used to do it at the end of the day, that way, if you use 1) the arp entry should have timed out by the morning. Better still you could inform all users to shutdown their machines that day when they leave work and then make the changes.

Jon

[garyrivers]

we're leaning towards #1 option.  with just shutting down the RTR and moving its IP to the SW.  and from what you're saying from there i'll have to let the arp tables refresh, or age out.

can't i clear the arp table to force a refresh?

Thanks

[Jon Marshall]

Yes you can but you would need to do that on each client. Thats why i suggested doing it in the evening after hours.

Jon

[garyrivers]

Jon, i haven't forgotten your advice.  i'm waiting for our maintenance window to enable routing, etc.

Thanks for your assistance.  Gary

[muhammadomer786]

Before doing that u have to make sure switch is ruuning a layer 3 (ip services) image.

Then just enable

conf t

ip routing

ip classless

router eigrp xx

hope this helps.

[garyrivers]

good thought! i checked the SW and it is running with ip services.

Thanks

[garyrivers]

thanks for the cmds.  i had forgotten about ip classless.

as i told Jon, i'm waiting for our maintenance window to open so when that happens i'll let you know how it turns out.

Thanks, Gary

[mrdogantr]

#conf t

(config)#ip routing

hth

Muammer