---
# System prepended metadata

title: 11-LAN security concepts
tags: [CCNA]

---

# Switch Security Configuration
## Secure Unused Ports
- To help secure the network from unauthorized access is to disable all unused ports on a switch.
```
Switch(config)# interface range type module/first-number – last-number
```
```
S1(config)# interface range fa0/8 - 24
S1(config-if-range)# shutdown
```
## Mitigate MAC address table attacks
- The most effective to prevent MAC address table overflow attack is to enable port security.
=> can control authorized access.
## Enable Port Security
- By default, Layer 2 switch ports are set to dynamic auto (trunking on) (choosing access or trunk mode).
=> use `switchport mode access` => allow to connect 1 VLAN or 1 device.
```
S1(config)# interface f0/1
S1(config-if)# switchport port-security
Command rejected: FastEthernet0/1 is a dynamic port.
S1(config-if)# switchport mode access
S1(config-if)# switchport port-security
S1(config-if)# end
S1#
```
```
S1# show port-security interface f0/1
Port Security              : Enabled
Port Status                : Secure-down
Violation Mode             : Shutdown
Aging Time                 : 0 mins
Aging Type                 : Absolute
SecureStatic Address Aging : Disabled
Maximum MAC Addresses      : 1
Total MAC Addresses        : 0
Configured MAC Addresses   : 0
Sticky MAC Addresses       : 0
Last Source Address:Vlan   : 0000.0000.0000:0
Security Violation Count   : 0
```
## Limit and Learn MAC addresses
```
S1(config-if)# switchport port-security ?
  aging        Port-security aging commands
  mac-address  Secure mac address
  maximum      Max secure addresses
  violation    Security violation mode  
```
 - `switch port-security maximum ...` => maximum number of MAC addresses allowed on a port.
 - `switchport port-security mac-address mac-address`=> manually configured MAC address for a port.
 - `switchport port-security` => dynamically learned.
 -  `switchport port-security mac-address sticky` => dynamically learned and "stick" them to configuration.
## Port Security Aging
```
Switch(config-if)# switchport port-security aging { static | time time | type {absolute | inactivity}}
```
![image](https://hackmd.io/_uploads/B1cwxVyVC.png)
```
S1(config)# interface fa0/1
S1(config-if)# switchport port-security aging time 10 
S1(config-if)# switchport port-security aging type inactivity 
S1(config-if)# end
S1# show port-security interface fa0/1
Port Security              : Enabled
Port Status                : Secure-up
Violation Mode             : Shutdown
Aging Time                 : 10 mins
Aging Type                 : Inactivity
SecureStatic Address Aging : Disabled
Maximum MAC Addresses      : 2
Total MAC Addresses        : 2
Configured MAC Addresses   : 1
Sticky MAC Addresses       : 1
Last Source Address:Vlan   : a41f.7272.676a:1
Security Violation Count   : 0
```
## Port Security Violation Modes
```
Switch(config-if)# switchport port-security violation { protect | restrict | shutdown} 
```
![image](https://hackmd.io/_uploads/HyLabVkER.png)
![image](https://hackmd.io/_uploads/rJaW7Vk4R.png)


# Mitigate VLAN Attacks
![image](https://hackmd.io/_uploads/B1Uzu4kVR.png)
## Step to mitigate VLAN Hopping Attacks
![image](https://hackmd.io/_uploads/B1zNuEk40.png)
![image](https://hackmd.io/_uploads/rk5VuNkEA.png)
![image](https://hackmd.io/_uploads/rJso_NJN0.png)

# Mitigate DHCP Attack
![image](https://hackmd.io/_uploads/HyzsQS1NR.png)
## DCHP snooping
![image](https://hackmd.io/_uploads/SkgRQSy4R.png)
## Steps to implement DHCP snooping
![image](https://hackmd.io/_uploads/rkRrESyER.png)
## Example
![image](https://hackmd.io/_uploads/BJMOVSkNC.png)
```
S1(config)# ip dhcp snooping
S1(config)# interface f0/1
S1(config-if)# ip dhcp snooping trust
S1(config-if)# exit
S1(config)# interface range f0/5 - 24
S1(config-if-range)# ip dhcp snooping limit rate 6
S1(config-if-range)# exit
S1(config)# ip dhcp snooping vlan 5,10,50-52
S1(config)# end
```
![image](https://hackmd.io/_uploads/rk01rByV0.png)
# Mitigate ARP Attacks
## Dynamic ARP Inspection
![image](https://hackmd.io/_uploads/ByVE8SyE0.png)
## DAI Implementation Guidelines
![image](https://hackmd.io/_uploads/H1PoYSkVA.png)
```
S1(config)# ip dhcp snooping
S1(config)# ip dhcp snooping vlan 10
S1(config)# ip arp inspection vlan 10
S1(config)# interface fa0/24
S1(config-if)# ip dhcp snooping trust
S1(config-if)# ip arp inspection trust
```
# Mitigate STP Attacks
![image](https://hackmd.io/_uploads/BkQrsry4C.png)
![image](https://hackmd.io/_uploads/r1kJhBJE0.png)
## Configure PortFast

=> **a risk of creating a spanning-tree loop**.

- PortFast can be enabled on an interface by using the spanning-tree portfast interface configuration command. Alternatively, Portfast can be configured globally on all access ports by using the spanning-tree portfast default global configuration command.

```
S1(config)# interface fa0/1
S1(config-if)# switchport mode access
S1(config-if)# spanning-tree portfast
%Warning: portfast should only be enabled on ports connected to a single
 host. Connecting hubs, concentrators, switches, bridges, etc... to this
 interface when portfast is enabled, can cause temporary bridging loops.
 Use with CAUTION
%Portfast has been configured on FastEthernet0/1 but will only
 have effect when the interface is in a non-trunking mode.
S1(config-if)# exit
S1(config)# spanning-tree portfast default
%Warning: this command enables portfast by default on all interfaces. You
 should now disable portfast explicitly on switched ports leading to hubs,
 switches and bridges as they may create temporary bridging loops.
S1(config)# exit
S1# show running-config | begin span
spanning-tree mode pvst
spanning-tree portfast default
spanning-tree extend system-id
!
interface FastEthernet0/1
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/2
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
! 
(output omitted)
S1#
```
## Configure BPDU Guard
- Even though PortFast is enabled, the interface will still listen for BPDUs. Unexpected BPDUs might be accidental, or part of an unauthorized attempt to add a switch to the network.
- If any BPDUs are received on a BPDU Guard enabled port, that port is put into error-disabled state. This means the port is shut down and must be manually re-enabled or automatically recovered through the errdisable recovery cause bpduguard global command.
- BPDU Guard can be enabled on a port by using the spanning-tree bpduguard enable interface configuration command. Alternatively, Use the spanning-tree portfast bpduguard default global configuration command to globally enable BPDU guard on all PortFast-enabled ports.
```
S1(config)# interface fa0/1
S1(config-if)# spanning-tree bpduguard enable
S1(config-if)# exit
S1(config)# spanning-tree portfast bpduguard default
S1(config)# end
S1# show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID           is enabled
Portfast Default             is enabled
PortFast BPDU Guard Default  is enabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is disabled
EtherChannel misconfig guard is enabled
UplinkFast                   is disabled
BackboneFast                 is disabled
Configured Pathcost method used is short
(output omitted)
```
# Some questions:
![image](https://hackmd.io/_uploads/SknlBL14C.png)
![image](https://hackmd.io/_uploads/ryquSIkEC.png)
![image](https://hackmd.io/_uploads/H1zcHUJVC.png)
![image](https://hackmd.io/_uploads/SkA9rLJ40.png)

