Administrative Distance, Access Lists, Route Manipulation, and IP Multicast - CCIE Routing and Switching Exam Certification Guide - page 475

Administrative Distance Configuration
To change the administrative distance for routing protocols, use the distance number command.
The number value ranges from 0 to 255. For OSPF, separate distances are configured for
external, intra-area, and internal routes. The command examples in Table 10-2 change the
administrative distances of routing protocols to a number between 40 and 50. (Don't do this on
a real internetwork!)

Use of the distance Command for Routing Protocols

Table 10-2

Protocol Commands

RIP

router rip
distance 49

IGRP

router igrp 100
distance 48

EIGRP

router eigrp 100
distance 41

IS-IS

router isis
distance 42

OSPF

router ospf 100
distance external 45
distance inter-area 46
distance intra-area 44

BGP

router bgp 6000
distance 47

Static routes have a default administrative distance of 1. There is one exception. If the static
route points to a connected interface, it inherits the administrative distance of connected inter-
faces, which is 0. Static routes can be configured with a different distance by appending the
distance value to the end of the command. The following command gives an administrative dis-
tance of 250 to the static route:

ip route 1.0.0.0 255.0.0.0 3.3.3.3 250 250

IP Access Lists
Many uses exist for IP access lists on Cisco routers and switches. You use access lists to control
access to networks and virtual local-area networks (VLANS), to redistribute or filter routes in
route maps, and so on. An access list defines a set of criteria that can be applied to every packet
processed by the router or switch.

When applied to an interface, an access list can block or permit traffic forwarding. The access
list can be applied at the ingress (inbound) or at the egress (outbound) of a network. If the list
is applied inbound, the system checks the access list's statements for a match when the router
receives a packet. If the packet is permitted, the system continues processing the packet
(checking the routing table and so on). If the packet is denied, it is discarded.