Though actually this simple topic is covered in CCNA, as this week just finish the teaching of CCNA, I still find that this really deserve to discuss.

The problem is about the VLAN configuration. In the new CCNA course, there is a lab about the inter-vlan router using the following topology:

Objective of the lab is quite simple, just use the Router to do inter-vlan routing. PC1 will be put on VLAN 10, while PC2 will be put on VLAN 20.
Now in SW1, create VLAN 10, configure port 0/1 to be VLAN 10. While port 0/3 and 0/13 need to be configured as trunk and allow VLAN 10,20 traffic. Configuration as below:

hostname SW1
!
vlan 10
!
interf FastEthernet 0/1
 switchport mode access
 switchport access vlan 10
 no shutdown
!
interf FastEthernet 0/3
 switchport mode trunk
 switchport trunk allowed vlan 1,10,20
 no shutdown
!
interf FastEthernet 0/13
 switchport mode trunk
 switchport trunk allowed vlan 1,10,20
 no shutdown

Similarly, in SW2, create VLAN 20, configure port 0/1 to be VLAN 20. While port 0/3 to be trunk, also allow VLAN 10,20 traffic. Configuration as below:

hostname SW2
!
vlan 20
!
interf FastEthernet 0/1
 switchport access vlan 20
 no shutdown
!
interf FastEthernet 0/3
 switchport mode trunk
 switchport trunk allowed vlan 1,10,20
 no shutdown
!

Now go to the Router, create 2 subinterfaces in interface 0/0 with VLAN 10 and 20 respectively. Configure the corresponding IP addresses - VLAN 10 uses subnet 10.1.10.0/24, while VLAN 20 uses subnet 10.1.20.0/24.

interface GigabitEthernet 0/0
 no shutdown
 description Link to LAN Switch
 ip address 10.1.1.1 255.255.255.0
!
interface GigabitEthernet 0/0.10
 encapsulation dot1q 10
 ip address 10.1.10.1 255.255.255.0
!
interface GigabitEthernet 0/0.20
 encapsulation dot1q 20
 ip address 10.1.20.1 255.255.255.0
!

Finally, for PC1 configure the corresponding IP address and default gateway as follows:

IP: 10.1.10.100 255.255.255.0
default gateway: 10.1.10.1

Similarly for PC2:

IP: 10.1.20.100 255.255.255.0
default gateway 10.1.20.1

OK, everything is ready? Should be able to ping between the PC1 and PC2.
Wait a miunte, lets first try to ping the default GW. In PC1, ping 10.1.10.1, perfectly works.
In PC2, ping 10.1.20.1. Hooops? Timeout!

So whats missing here? You may already able to figure it out. Problem is in SW1. It misses the VLAN 20. Though it doesn't has any access port on VLAN 20, it still needs to pass VLAN 20 traffic. Without the VLAN 20 definition, in fact, it won't carry VLAN 20 traffic on the trunk between it and the router. Thus VLAN 20 traffic is dropped and won't send to router.

To fix it:

sw1(config)# vlan 20

Recently, I have tested the F5 (Big IP) LTM v11.4 SNMP configuration and my snmpscan tools. Here is the steps. 

1. In the F5 LTM admin webpage, select the SNMP->Agent->Configuration

2. In the configuration page, need to add your SNMP management software subnet (or starting octets).

3. Then go to the "access (v1,v2c)" screen (of course can use v3). Create a new access.

4. In the access creation screen, you define the community string. Yet, what I want to point out is that if you want to restrict the OID branch that this community allows, first the OID syntax begins with a dot. E.g. for MIB-2, enter ".1.3.6.1.2.1". Secondly, need to select the source IP  that allow access.

5. Now, you can download my free snmpscan tools under IPtools. Enter the IP of your F5, comunity and OID. Click the start scan, now you get the values of the MIB tree branch as below: