vlan not working correctly

[Joli Martinez]

Hello,

I have an 1841 router where interface 0/0 is connected to my DSL connection.  0/1.10 is one of my assisnged public IP's and 0/1.20 is my LAN ip.  When I physically connect my internet direct to 0/0 everything works correctly.  But when I plug 0/0 into my 3560 switch and a cable back to 0/0 it stops working.  

I have created a sparate vlan for my DSL connection and just those two ports are on them.  Why does it not work?  What am I missing?

It works for a couple of minutes then just dies.  I have tried to rearp the devices and sometimes it works for a couple of min then pinging 4.2.2.2 ttl time goes up and up to about 4000ms then eventually dies.

Router

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

interface FastEthernet0/0
ip address dhcp
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
no cdp enable
!
interface FastEthernet0/1
no ip address
ip virtual-reassembly
duplex auto
speed auto
!
interface FastEthernet0/1.20
encapsulation dot1Q 20 native
ip address 10.21.20.254 255.255.255.0
ip nat inside
ip virtual-reassembly
!
interface FastEthernet0/1.10
encapsulation dot1Q 10
ip address 1.1.1.1 255.255.255.248
ip virtual-reassembly

Switch

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

interface GigabitEthernet0/47

description Router Connection
switchport access vlan 50
switchport mode access
spanning-tree portfast
!
interface GigabitEthernet0/48
description MAIN INTERNET CONNETCION
switchport access vlan 50
switchport mode access
spanning-tree portfast

[paul driver]

Hello

I can see vlan 50 created on switch but not on the router - only vlan 10-20

On switch:

1) configure a trunk interface on the switch port that connects to the router

2) disable IP routing

3) create  l2 vlan 10,20

4)assign an access port  to eeither vlan  10 or 20

Res

paul

[Joli Martinez]

Vlan 10 and 20 is for my LAN side.  This is working correctly.  This is on interface 1.10 and 1.20.  My issue is on interface 0/0.  My switch has all three vlans configured.

10,20, and 50.  but only 50 has no ip on the switch and two ports on it.  this should just be L2 traffic.

[Iulian Vaideanu]

When things stop working, are all interfaces involved in Vlan50 up, and does Fa0/0 on the 1841 still have an IP address?  What does "show ip dhcp snooping" look like on the switch?

[Joli Martinez]

I have routing turned on on the switch for my other vlans to route to each other.  When I plug the DSL modem to the switch it doesnt automatically come up.  I have to initiate a ping to the DSL modem, then it comes up for a while and ping times start increasing and then eventually dies.  From the LAN side of the router I am still able to ping the internet, but on the switch I am not able to ping out or to the LAN side of the DSL.

This is the output of the dhcp snooping on the switch.

L3Switch#sh ip dhcp snooping
Switch DHCP snooping is disabled
DHCP snooping is configured on following VLANs:
none
DHCP snooping is operational on following VLANs:
none
Smartlog is configured on following VLANs:
none
Smartlog is operational on following VLANs:
none
DHCP snooping is configured on the following L3 Interfaces:

Insertion of option 82 is enabled
circuit-id default format: vlan-mod-port
remote-id: 0016.4689.4180 (MAC)
Option 82 on untrusted port is not allowed
Verification of hwaddr field is enabled
Verification of giaddr field is enabled
DHCP snooping trust/rate is configured on the following Interfaces:

Interface Trusted Allow option Rate limit (pps)
----------------------- ------- ------------ ----------------
L3Switch#

[paul driver]

Hello

But when I plug 0/0 into my 3560 switch and a cable back to 0/0 it stops working.

So you are plugging the iISP dsl  connection from the router into the switch  then cabling an access port back to the dsl correct?

[Joli Martinez]

yes that is correct.