Very basic layer 3 setup on 3550?

[isparks_curtis]

We recently added another colocation provider to our operation and this new provider required us to provide and configure our own layer 3 switch so that our network traffic (arp requests and such) stay off their router.   We got a used 3550 upon their recommendation.

I've got the switch on the rack and am just starting the configuration (which I'm doing remotely). I thought that since it's such a basic setup that we need, that it would be a pretty simple process.  However the switch has so many features, I'm not sure where to start.

Our provider gave us the following information for configuring the switch (ips masked for security):

Public IP:

xxx.xxx.xxx.32/30
xxx.xxx.xxx.32 Network address – unusable
xxx.xxx.xxx.33 Provider's Interface
xxx.xxx.xxx.34 cisco switch external IP
xxx.xxx.xxx.35 Broadcast address – unusable

They also gave us another block of IPs in a separate subnet for assigning to our servers.  When I first brought up the CLI (via a serial console) it went right into a basic configuration tool.  Assuming the above IP was what I used for the management interface, I responded to the switch's basic configuration questions as follows:

-------------------------------------------------------------------------------------------
Enter interface name used to connect to the
management network from the above interface summary: FastEthernet0/48

Configuring interface FastEthernet0/48:
  Configure IP on this interface? [no]: yes
    IP address for this interface: xxx.xxx.xxx.34
    Subnet mask for this interface [255.0.0.0] : 255.255.255.252
    Class A network is 108.0.0.0, 30 subnet bits; mask is /30
Would you like to enable as a cluster command switch? [yes/no]: no

-------------------------------------------------------------------------------------------

Questions:

1. Why does it think I configured a class A network when I entered a mask of 255.255.255.252?

2. Do I need to tell the switch about the IP block assigned to our servers?  If so, how?

3. What do I do to enable the layer 3 routing so that arp requests, etc from our servers stay off our provider's router?

Thanks,

Curtis

[sansarav720e]

Hi Curtis ,

Here is ur config for ue requirement

connected your new provider to your L3 switch as directly routed interface

interface fastethernet 0/48

no switchport

ip address xxx.xxx.xxx.34 255.255.255.252

no shut

you created an l3 SVI on your switch for server block (eg u have got block : 192.168.1.0/29)

interface vlan 80

no shutdown

ip address 192.168.1.1 255.255.255.248

interface range fastethernet 0/1 - 5

switchport mode access

switch port access vlan 80

connect your server to interface 0/1 - 5 assign ip address .2 to 6 with SM 255.255.255.248 and GW 192.168.1.1

for ip routing enable command

ip routing

similarly u need to have default route pointing ur service provider

ip route 0.0.0.0 0.0.0.0 xxx.xxx.xxx.33

Questions:

1. Why does it think I configured a class A network when I entered a mask of 255.255.255.252? : Service provider always use VLSM 

2. Do I need to tell the switch about the IP block assigned to our servers?  If so, how? : As i said before use SVI config

3. What do I do to enable the layer 3 routing so that arp requests, etc from our servers stay off our provider's router?: ip routing

HTH

Thanks

san

[isparks_curtis]

Very helpful... thanks, San! :-)

Curtis

[isparks_curtis]

San, thanks to your help, the setup of the switch went very smoothly.

Another question... if we get a second block of IPs from our provider that are in a different subnet, what would be the best way to make the additional ips available on the same ports as the first block?

Thanks again,

Curtis

[sansarav720e]

Hi Curtis ,

                If have a additonal block for ur segment you can define another L3 SVI on your switch  ( IP BLock : 192.168.100.0 /28)

interface vlan 90

no shut
ip address 192.168.100.1 255.255.255.240

if u want have on same port where first block is connected . u can enable trunk on switch ports (Note : if u enable trunk also only one VLAN will work when its connected to workstation or server ) . On trunk port u can have your native vlan pointing vlan 80 or 90 ,if trunk fails it has priority to vlan 80 or 90  ,But only native vlan works , not both vlan will work at a time . Better to have separate switch port for this extra ip block

interface range fastethernet 0/1 - 5
switch mode trunk
switch mode trunk native vlan 80

simialrly reverse route is to pointed from your service router to your L3 Switch for this extra ip block

SR router # ip route 192.168.100.0 255.255.255.240 x.x.x.34 (interface of ur L3 switch )

HTH

THanks
SAN