Need help with DHCP and intervlan on cisco switch 3550

Question:

I am trying to WS-C3560X-48P-S setup my 3550 layer 3 switch to do hand out dhcp addresses for different vlans.  It is connected to my router address 192.168.1.1.  I setup a new vlan 3 and the dhcp pool.. The client gets a 192.168.3.2 address but am not able to ping the router and other clients and get out to the internet.  What am I doing wrong?  I will appreciate any help or advice.  Here is the config that I have.  I deleted the other ports because I am not using them.  The vlan 3 client is on port fast Ethernet 0/17 and the router is connected to the fastethernet 0/1.  Thanks in advance.

version 12.2

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname SW3

!

no aaa new-model

ip subnet-zero

ip routing

no ip domain-lookup

!

ip dhcp pool VOICE_VLAN

   network 192.168.3.0 255.255.255.0

   default-router 192.168.3.1

   dns-server 192.168.1.1

   option 150 ip 192.168.3.1

!

no file verify auto

spanning-tree mode pvst

spanning-tree extend system-id

!

vlan internal allocation policy ascending

!

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

!

!

interface FastEthernet0/17

switchport access vlan 3

switchport mode access

spanning-tree portfast

!

interface GigabitEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

!

interface GigabitEthernet0/2

switchport trunk encapsulation dot1q

switchport mode trunk

!

interface Vlan1

ip address 192.168.1.223 255.255.255.0

!

interface Vlan3

ip address 192.168.3.1 255.255.255.0

!

ip default-gateway 192.168.1.1

ip classless

ip route 0.0.0.0 0.0.0.0 192.168.1.1

ip http server

ip http secure-server

!

!

!

control-plane

!

!

line con 0

exec-timeout 0 0

line vty 0 4

no login

line vty 5 15

no login

!

end

Answer:

YFor VLAN 1 - default gateway is 192.168.1.1 (Router)

For VLAN 3 - default gateway is 192.168.3.1 (SW)

so when VLAN 3 users try to talk to Router IP 192.168.1.1, then the traffic goes to the Router (via the SW which is the default gateway for users in VLAN 3)

But as you specified that there is no back route for 192.168.3.0/24 on router - the traffic destined to this subnet on Router will go the default route and the pings are never going to work between these 2 VLAN's.

So to avoid this, you will need to have the default gateway for both the VLAN's on the SW (as the router is not managed)

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