Cisco IOS & Commands - caitlinmallen/TechWiki GitHub Wiki

Cisco IOS & Commands

What is Cisco IOS?

Cisco Internetworking Operating System
Now used on most Cisco switches and routers
- Some Cisco security appliances use a Linux-derived OS instead of Ciscso IOS

Cisco IOS Config File
Cisco IOS configurations are thought of as one big file

When entering a configuration command, you are essentially editing the file by adding, removing, or editing lines
Essentially two versions of the configuration file
- Starup-config
  - Last version of what was saved. If the router/switch is restarted, these configurations would still load.
- Running-config
  - Stored in memory and is not saved after power down.
  - To save running-config permanently there are two options:
    - copy running-config startup-config
    - copy run start\

CIOS Command Modes There are different "levels" of command and configuration options

User EXEC Mode
- Basic monitoring and status commands
- Would see 'Router>' displayed
Privileged EXEC Mode
- Admin/root access
- Would see 'Router>#' displayed
Global Config Mode
- Device-wide configuration settings
- Would see 'Router(config)#' displayed
Interface Config Mode
- Configure interface settings
- Would see 'Router(config-if)#' displayed\

Cisco IOS Helpful Tips

Up arrow displays last entered commands
Type '?' in current mode to see all options you can type or complete an existing command
TAB autocompletes

Access Ports
configure - terminal
- (configure-if)#interface [port_name-number]
- (configure-if)#switchport mode access
- (configure-if)#switchport access vlan [vlan-id#]
Trunk Ports
- configure - terminal
- (configure-if)#interface [port_name-number]
- (configure-if)#switchport mode trunk
- (configure-if)#switchport trunk allowed vlan [vlan-range]

ip helper-address is important to remember
When assigning the IP helper address, use the eth0 interface IP of the DHCP server, that is the server address *(config)# interface vlan [vlan_id#] *(config-if)# ip helper-address [DHCPServer_Address]

Inside is the interface connected to the private address, outside connected to the public address
interface fastEthernet 0/0
ip nat inside
exit
#interface serial 0/0/0
(config-if)# ip nat outside
exit

Configure network (if applicable)
1. Check subnets
2. Assign IPs
3. Assign proper gateways to routers, if multiple, increase last octet by 1 to make sure packets can flow between routers and to machines
  1. Check machines to make sure they have proper gateways
4. Enable interfaces on routers
5. Get wildcard masks of subnets
  1. Google it or check Wiki for how to do that if Adam says no Google :/
Configure OSPF on routers
1. Enter the Cisco IOS command line
2. enable > router ospf [instance_number] (Just put 1 for ease)
3. Network [network_address] [wildcard_mask] area 0
Do this on all routers for each subnet they are on
Make sure machines can ping
Enter back into routers to define a keychain
enable > configure terminal
key chain [name]
key [key-id]
key-string [name]
cryptographic-algorithm [algorithm]
send-lifetime [start-time] { infinite | end-time | duration seconds}
Now we need to define authentication
interface [type] [number]
ip ospf authentication key-chain [name]

Define router instance
1. router bgp AS_Number_for_Router
2. router bgp 1010
Identify peers
1. (config-router) neighbor ip_of_peer remote-as as-number_of_peer
2. (config-router) neighbor 192.168.1.2remote-as 2352
Advertise Networks
1. (config-router) network 10.10.52.0mask 255.255.255.0
If configuring redistribution of OSPF on border router
1. To advertise networks shared through OSPF, the following command needs to be included in the BGP configuration
2. redistribution ospf instance_number