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Need Advice/Assistance w/ Resegmenting a Network

hyounkim80
Beginner
Beginner

I'm a new hire at my place of employment, in which I work at a branch office. Upon arriving, I was told that the network wasn't exactly running up to par with occasional hitches in the network. After doing some investigation, I found the that all the Cisco networking equipment is using VLAN 1 with multiple physical links between everything. Eventually, the connections go back to a C3640 router.

The C3640 router uses EIGRP to connect to other routers outside our location in which we also get our Internet connection. The main office has configured the router and I'm mainly responsible for everything internal to our branch. We have 4 subnets that we use internally:

176 - Datacenter

177 - Device Management

216 - Tech/Servers

229 - Users

The physical link to the router is defined as follows:

interface FastEthernet0/0

description LAN segment

ip address 172.24.216.254 255.255.255.128 secondary

ip address 172.24.229.254 255.255.255.128 secondary

ip address 172.24.216.254 255.255.255.0 secondary

ip address 172.24.217.254 255.255.255.0 secondary

I believe the problem is that all traffic, especially heavy traffic from the datacenter, has to go through this old router before reaching the other subnets. We have several gigabit capable switches here capable of routing. My idea is to move all the subnets to the C3750 & C4948 switches and allow the routing to be processed on those two switches. That leaves the C3640 to be only used for connections outside out network, such as to corporate or the Internet.

I want to resegment the network to 4 individual VLANs. I have a C3750 that I would like to be the main router for subnets 229 & 177 but would also provide a hub-spoke connectivity to all the other switches in the office. I also have a C4948 switch that I would like to be the router for subnets 176 & 216. If I am to do this, could I potentially just define everything via static routes or would you suggest using a routing protocol?

Any help would be appreciated.

21 Replies 21

Jon Marshall
VIP Community Legend VIP Community Legend
VIP Community Legend

Your approach is a good one but i'm not clear why you want to route the internal subnets using 2 different switches.

Personally i would choose the 3750 and route all vlans off the switch. Then have a L3 routed connected to the 3640. This way you could indeed if you wanted use static routes and it would be relatively straightforward ie.

L3 connection between 3750 and 3640 -

3640

====

int fa0/0

ip address 192.168.5.1 255.255.255.252

3750

====

int gi0/1

ip address 192.168.5.2 255.255.255.252

then routing -

on the 3750

ip route 0.0.0.0 0.0.0.0 192.168.5.1

on the 3640

ip route 192.168.5.2

for each of the internal subnets being routed off the 3750.

You could just as easily run a routing protocol such as EIGRP although that does depend on the feature set in use on your 3750.

Jon

Thanks Jon. Your reply was extremely helpful and I rated it accordingly.

The reason I wanted to split Datacenter traffic from the C3750 to another switch is because I didn't want the C3750 to get overloaded by the everyday traffic from the servers. I thought by isolating the traffic on its own switch, it could free up resources on the C3750.

Of course, if you think the C3750 can handle that with ease, then I can go ahead and just put all the VLANs on the C3750.

The C3750 is a C3750G-12S-E switch running c3750-ipservices-mz.122-52.SE.

With your example, it seems I'll just be using static routes. In your opinion, would it be necessary to use a routing protocol when only 2 "routers" are connected to each other?

Also is there anything else I need to do specifically in regards to routes and the interfaces? Or is your example all that is needed (for example do I need to put the interfaces on switchport mode access, switchport access vlan )?

"The reason I wanted to split Datacenter traffic from the C3750 to another switch is because I didn't want the C3750 to get overloaded by the everyday traffic from the servers. I thought by isolating the traffic on its own switch, it could free up resources on the C3750."

So you have servers in your branch office that talk to the data centre ??. If so be aware that it will very probably be the WAN connection and not the internal switch that becomes the bottleneck. If there was a lot of chatter between servers within your branch then yes i would connect them to the 4948 but if they were all in the same vlan then they could still route off the 3750.

Perhaps you clarify exactly how the setup works ie.

Do you know how much traffic is sent between servers

Is this traffic local to the servers within your branch or remote

Are the servers in your branch all in the same vlan

Where is the location of your data centre or is this just a label ?

"With your example, it seems I'll just be using static routes. In your opinion, would it be necessary to use a routing protocol when only 2 "routers" are connected to each other?"

Not necessary no. And with the number of vlans you have internally it is easily manageable with static routing. Dynamic routing would be more useful if you had a lot more

i) vlans

ii) routers

or you had redundant links and you let the routing protocol work out the best path.

One other option i didn't mention was that you could use the 4948 with the 3750 and

i) run HSRP between them

ii) dual connect your servers for NIC redundancy, but still need to understand server situation a little better

What i provided in config was for routing purposes. You would need to -

1) configure trunk links to other switches

2) configure STP root for vlans on 3750

3) as you say configure the ports with end devices into their respective vlans.

Jon

Oh no... sorry for not being clear. All the subnets I mentioned earlier exist only in my office. The datacenter is in my office as well. All networking equipment is within walking distance and use MM fiber to connect to the C3750.

In the Datacenter, the majority of our servers use 2+ gigabit interfaces bonded by etherchannel. The servers themselves are various file servers, database servers, that are backed up daily to a backup server. We also utilize a fiber channel SAN setup. In addition, we also have a DR setup that is identical to the production servers. I just assumed that putting all those servers on the C3750 would eat up the link utilization and processor utilization.

A few weeks ago, every subnet was on VLAN 1 going to the C3640 router. I split all the subnets into their own VLAN, but they still go to the C3640. That's why I was looking for advice on how to migrate it off the C3640 to the C3750/C4948. But with your opinion & recommendation, I think I'll just use the C3750 as a router for the internal network and then the C3640 as the router to the outside.

I have set up HSRP before on 2 C3750s, so I could do it for the C4948 & the C3750 but... the C3750 is strictly fiber only (the C3750G-12S model), so I couldn't connect the servers redundantly. With that in mind, the HSRP would only be failover solution in case the C3750 goes down. But in that event, it wouldn't really make sense to do that because the C4948 doesn't have the capacity for being an uplink switch for the other switches in the office due to the lack of fiber ports.

Okay, thanks for clearing that up. I was a little confused because you said it was a branch office.

I would connect the servers to the 4948 switch but still route the server vlan(s) off the 3750. If you find that the utilization on the 3750 is too high you can migrate the L3 vlan interfaces for the servers onto the 4948 at a later date.

Agree with what you say about HSRP and the switches. Wouldn't make a lot of sense if you can't uplink the access-layer switches to the 4948.

Jon

Thanks for all your help Jon.

For clarification purposes, on the C3640, you give the example of:

=========

int fa0/0

ip address 192.168.5.1 255.255.255.252

ip route 192.168.5.2

=========

When I log into my C3640, I only see the following available:

C3640(config)#ip route ?

A.B.C.D Destination prefix

profile Enable IP routing table profile

static Allow static routes

vrf Configure static route for a VPN Routing/Forwarding instance

I don't see an option to put a VLAN # in the ip route command, unless you're talking about the network itself. For example: 'ip route 172.24.176.0 255.255.255.0 192.168.5.2'. If this is the case, would specify the static route for each subnet on the C3750? I have 4 networks internally (172.24.176.0/24, 172.24.177.0/24, 172.24.216.0/28, 172.24.229.0/28).

Also, do I have to specify a VLAN interface on the C3750 for the link between the C3640 & the C3750? Or do I just strictly put what you mentioned in your example.

So if what I mentioned is correct, I am assuming that I have the following lines in my configuration:

=========

C3640

=========

int fa0/0

ip address 192.168.5.1 255.255.255.252

!

ip route 172.24.176.0 255.255.255.0 192.168.5.2

ip route 172.24.177.0 255.255.255.0 192.168.5.2

ip route 172.24.229.0 255.255.255.128 192.168.5.2

ip route 172.24.216.0 255.255.255.128 192.168.5.2

=========

C3750

=========

!

int gi0/1

ip address 192.168.5.2 255.255.255.252

!

ip route 0.0.0.0 0.0.0.0 192.168.5.1

"Thanks for all your help Jon."

No problem, glad to be of help.

"I don't see an option to put a VLAN # in the ip route command, unless you're talking about the network itself. For example: 'ip route 172.24.176.0 255.255.255.0 192.168.5.2'. If this is the case, would specify the static route for each subnet on the C3750?"

Correct, i mean you put the IP subnet and the subnet mask in the route statements on the 3640. Yes you would specify a route for each subnet on the 3640.

"Also, do I have to specify a VLAN interface on the C3750 for the link between the C3640 & the C3750? Or do I just strictly put what you mentioned in your example."

On the 3640 just remove all the existing IP addressing and add the new one.

On the 3750 you would do

int gi0/1

no switchport

ip address 192.168.5.2 255.255.255.252

also don't forget to enable ip routing on the 3750 ie.

3750(config)# ip routing

Your config is spot on with the addition of the "no switchport" under the gi0/1 interface.

Jon

Hey Jon, I don't know if you're available, but I plan on doing this change tonight. I'm 99.9% certain this will go without a hitch.

Basically what I plan on doing is logging into the C3640 and performing a "show ip arp" so I can get the IPs of every machine/device we have on the network matched to their respective MAC addresses. Then I'll trace the MAC addresses across all our switches so when I do the change, I can just change the switchport VLAN from 1 to the new VLAN.

One thing to note though is that I notice that the router interface where all the subnets exist also has one other network on it that is not a part of our internal branch network. I believe the IP subnet belongs to devices the main office. I mentioned that our router is using EIGRP and is interconnected with other routers within the organization. So here is the config:

interface FastEthernet0/0

description LAN segment

ip address 10.10.1.254 255.255.255.0 secondary

ip address 10.100.131.254 255.255.255.0 secondary

ip address 172.16.216.254 255.255.255.128 secondary

ip address 172.16.229.254 255.255.255.128

ip address 172.16.176.253 255.255.255.0

ip address 172.16.177.253 255.255.255.0

ip access-group Virus in

ip helper-address 172.16.213.162

ip helper-address 172.16.208.34

ip accounting access-violations

ip flow ingress

ip pim dense-mode

load-interval 30

duplex auto

speed auto

Is it ok for me to leave the 10.xxx.xxx.xxx network intact on that interface and just add what we discussed earlier (the 192.xxx.xxx.xxx address) between the C3750 & the C3640? I shouldn't have any problems right?

"Hey Jon, I don't know if you're available, but I plan on doing this change tonight. I'm 99.9% certain this will go without a hitch"

I'm in UK so it's already evening here. I may be around as i have bad toothache at the moment so not sleeping too well but can't guarantee it.

The 10.x.x.x network, yes you can leave it on the interface but you should find out for sure what it is being used for before making the change. Doesn't sound right that you have this on your interface and yet the subnet belongs to a remote site.

Also a couple of other things -

1) you will need to move the ip helper-addresses to the L3 vlan interfaces you create on the 3750.

2) You have "ip pim dense-mode" on this interface. Do you know if that is actually in use because you will also need to enable this on the 3750 and then you do need the IP Services image to run multicast. If multicast is in use you will also need to migrate this commmand to each L3 vlan interface.

If you are comfortable with all the additional things above then good luck with the change tonight but -

if you are not it may well be worth postponing as this would also give you the time to track down all the mac-address to IP mappings and which switches they are on. This could be done during production hours and then you can have a text file with the correct config per switch which could just be cut and pasted in.

Personally i would do all this mac to IP mapping in advance of the change which will give you more time to troubleshoot other issues should it not go as planned.

Jon

Hey Jon,

The network changes ended up being a failure. I configured both devices exactly how we discussed and the C3640 & C3750 were aware of the new routes. The routes for each network were displayed as directly connected and all devices were pingable. However, all subnets on the C3750 were no longer able to ping/connect to the main office or the Internet. Essentially, they were unable to get outside of our office network.

One thing to note is that the C3640 is connected to the next router (outside our network) via EIGRP. I'm not too keen on EIGRP, but here's how it's defined on the C3640 router (with IPs changed of course):

router eigrp 20

network 10.1.65.0 0.0.0.255

network 10.1.86.0 0.0.0.255

network 172.16.0.0

distribute-list Route_Distribution out FastEthernet0/1

no auto-summary

I know I'm missing something stupid… Because when I rolled back my changes and took out the lines I specifically mentioned above, everything goes back to normal. The only thing that changed with my changes is that the default router for our networks changes from the C3640 to the C3750. I'm 99.9% sure that something is wrong specifically with the EIGRP configuration. The C3640 is aware of the statically routed networks, but it's not being redistributed through EIGRP. That distribute-list line is an access list with a bunch of subnets (ours included) defined on it, so I'm pretty sure it has nothing to do with access.

What do you think?

Which interface connects to the main office on your WAN router ?

The reason you couldn't connect to the main office is because the 172.x.x.x networks have moved to the 3750 so your 3640 no longer advertises them to the main office.

Apologies, should have taken this into account.

There are 2 ways around this although i still need to know a bit more info about the distribute list.

1) On the 3640 under the EIGRP config add the following line -

router eigrp 20

redistribute static

this will make your EIGRP process tell the main office about the 172.x.x.x subnets that you have added static routes for on the 3640

2) Run EIGRP between the 3640 and the 3750. Again as i said this does depend on the image on your 3750. Perhaps best to try 1) first.

Good luck.

Jon

Hey Jon. I assumed solution #1 after I wrote you and did some research. however, I notice some examples on Cisco.com specify the metric in EIGRP when redistributing across other routing protocols.

Specifically: default-metric 10000 100 255 1 1500

Do I have to specify the default metric? If so, does the above line look ok? I got it from Cisco's site for an ethernet link... however I'm wondering why the load is specified as a 1.

Thanks again!

Oh, I forgot to mention that our WAN link goes out of interface f0/1, which only has an ip address specified in its configuration.

I'll try the suggested changes and let you know how it goes.

Thanks again for your help.

Just seen this additional post.

You need to check the distribute list because it applies to routes going out to the main office. Make sure it does not filter any of your internal networks although it shouldn't as it obviously worked before.

Jon

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