Cisco Router
# help
?
# enable the privileged exec
enable
# exit from the privileged exec
disable
# modify system wide configuration, should enter global configuration mode
configure terminal# change interface
interface FastEthernet0/0# enable ip forwarding
ip routing
# disable ip forwarding
no ip routing# enable or disable an network interface
no shutdown
shutdown# set subnet
ip address 10.0.1.1 255.255.255.0# check interface setting
show ip int brief# Privilege mode
# show ip route
show ip route
# clear all ip route
clear ip route *
# show ip cache
show ip cache# static route setting
# Means 10.0.3.0/24 are from 10.0.2.2
ip route 10.0.3.0 255.255.255.0 10.0.2.2#arp#in privileged exec
show arp
clear arp-cache# global config# set router default gateway
ip default-gateway xxx.xxx.xxx.xxx
PC
# set Network mask
ifconfig eth0 netmask 255.255.255.0# set up static route
# make it permanent use -> /etc/sysconfig/static-routes# add static route in host
# 10.0.1.0 => other subnet
# 255.255.255.0 => netmask
# 10.0.3.1 => router interface
route add –net 10.0.1.0 netmask 255.255.255.0 gw 10.0.3.1
# display route
route -e
Problem Solving
Q: A change in the routing table has no effect on the flow of traffic.
A: The ARP table has old entry. arp -d ip_addr
Q: Traffic does not reach destinations on local subnet.
A: Network interface does not configure correctly
Q: ICMP request messages reaches destination, but ICMP reply does not reach source.
A: Reverse Routing table has some IP forwarding problem
# trace route
traceroute 10.0.1.1
Save settings in GNS3
VM Config
# eth0 as an exampleauto eth0iface eth0 inet staticaddress 10.0.1.10netmask 255.255.255.0gateway 10.0.1.1# up echo nameserver 192.168.0.1 > /etc/resolv.confpost-up route add -net 10.0.2.0 netmask 255.255.255.0 gw 10.0.1.1
Router config
# exec mode
copy running-config startup config