Editing Cisco Commands (section)

= Routing =

Routing is the process of forwarding packets between different networks using routing tables and routing protocols.

=== Enable IP Routing (Layer 3 Switch) ===
Required on multilayer switches to allow routing between VLANs.

 ip routing

=== Enable IPv6 Routing (Routers) ===

 ipv6 unicast-routing

== Static Routing ==

=== Configure a Static Route ===
Manually define a path to a remote network. Here's an example using the default administrative distance value.

 ip route 192.168.2.0 255.255.255.0 192.168.1.1

Manually define a path to a remote network and specify the administrative distance.

 ip route 192.168.2.0 255.255.255.0 192.168.1.1 10

Format:

 ip route <destination-network> <subnet-mask> <next-hop-ip> <administrative-distance (optional)>


=== Configure a Fully Specified Static Route ===
A fully specified static route includes both the next-hop IP address and the exit interface. This is commonly used on multi-access networks.

Example:

 ip route 192.168.2.0 255.255.255.0 GigabitEthernet0/0 192.168.1.1

You can also specify the administrative distance:

 ip route 192.168.2.0 255.255.255.0 GigabitEthernet0/0 192.168.1.1 10

Format:

 ip route <destination-network> <subnet-mask> <exit-interface> <next-hop-ip> <administrative-distance (optional)>

=== Configure a Default Route / Default Gateway ===
Route used when no specific route matches the destination.

 ip route 0.0.0.0 0.0.0.0 192.168.1.1

 ipv6 route ::/0 2001:ABC:33:44::1

== Administrative Distance ==

Determines which route is preferred when multiple routes to the same destination exist.

Common values:
 Connected – 0
 Static – 1
 EIGRP – 90
 OSPF – 110
 RIP – 120

Chart pulled from https://en.wikipedia.org/wiki/Administrative_distance#Default_administrative_distances
{| class="wikitable" style="text-align:center"
! Routing protocol !! Administrative distance
|-
| Directly connected interface || 0 (Only the interface itself has an administrative distance of 0, since a route cannot have a distance of less than 1.)
|-
| Static route || 1
|-
| Dynamic Mobile Network Routing (DMNR) || 3
|-
| EIGRP summary route || 5
|-
| External BGP || 20
|-
| EIGRP internal route || 90
|-
| IGRP || 100
|-
| Open Shortest Path First (OSPF) || 110
|-
| Intermediate System to Intermediate System (IS-IS) || 115
|-
| Routing Information Protocol (RIP) || 120
|-
| Exterior Gateway Protocol (EGP) || 140
|-
| On Demand Routing (ODR) || 160
|-
| EIGRP external route || 170
|-
| Internal BGP || 200
|-
| Next Hop Resolution Protocol (NHRP) || 250
|-
| Default static route learned via DHCP || 254
|-
| Unknown and unused || 255 (An administrative distance of 255 causes the router to remove the route from the routing table and not use it.)
|}

== Dynamic Routing ==

Dynamic routing protocols automatically exchange routing information between routers.

=== Configure RIP v2 ===
Uses hop count as metric (maximum 15 hops).

 router rip
  version 2
  no auto-summary
  network 192.168.1.0


=== Configure EIGRP ===
Uses bandwidth and delay as composite metric.

 router eigrp 100
  no auto-summary
  network 192.168.1.0 0.0.0.255


=== Configure OSPF ===
Link-state protocol using cost as metric.

 router ospf 1
  network 192.168.1.0 0.0.0.255 area 0


== Route Summarization ==

Route summarization (aggregation) reduces routing table size by advertising one route that represents multiple networks.

Example networks:
 192.168.0.0/24
 192.168.1.0/24
 192.168.2.0/24
 192.168.3.0/24

Can be summarized as:
 192.168.0.0/22


=== Configure Manual Summarization (EIGRP) ===
Applied on the outgoing interface.

 interface GigabitEthernet0/0
  ip summary-address eigrp 100 192.168.0.0 255.255.252.0


=== Configure Manual Summarization (OSPF ABR) ===
Configured under the OSPF process (on an ABR).

 router ospf 1
  area 0 range 192.168.0.0 255.255.252.0


== Show Routing Information ==

=== View Routing Table ===

 show ip route


=== View Specific Route ===

 show ip route 192.168.1.0


=== View Routing Protocol Information ===

 show ip protocols