This article was first written in August 2004 for the BeezNest technical website (http://glasnost.beeznest.org/articles/167).
GRE tunnels between Cisco and Linux (2.4 and up) routers are possible.
Given the following two routers, each one gateway for its network:
Public IP: 126.96.36.199
Private network: 192.168.4.0/24
IP on that private network: 192.168.4.4
Public IP: 188.8.131.52
Private network: 192.168.10.0/24
IP on that private network: 192.168.10.4
See IP in IP or GRE tunnel using iproute for the Linux configuration part.
For the Cisco part, it is quite similar, as the needed portion of configuration is something like this:
interface Tunnel1 description connection to Linux Network ip address 192.168.10.4 255.255.255.0 tunnel source Dialer1 tunnel destination 184.108.40.206 tunnel mode gre ip
Where Dialer1 is the name of the interface of the Cisco router connected to Internet (it’s used to always match the actual and current public IP of the router).
This article was first written in April 2004 for the BeezNest technical website (http://glasnost.beeznest.org/articles/121)
Log into the machine (using telnet for example).
Change to enable mode.
Change to configuration terminal mode:
# conf term
Issue the following command to redirect port 22/tcp from the outside interface (address) to the inside machine you would like the connection to get to:
(config)# ip nat inside source static tcp 192.168.0.7 22 220.127.116.11 22
First IP is the inside local IP address (inside the LAN, only reachable locally, so internal IP addressing) then the inside port on which to connect followed by the IP address of the outside global IP address then the port on which you want to reach that device.
Press <<ctrl-Z>> to exit the configuration terminal mode.
Issue the following command to apply and save the configuration on the flash (disk):
# write running
This article was first written in July 2005 for the BeezNest technical website (http://glasnost.beeznest.org/articles/280).
Here is an example on how to configure a DHCP server on a Cisco router.
ip domain-name 18.104.22.168 ip dhcp excluded-address 192.168.64.1 ip dhcp excluded-address 192.168.1.7 ip dhcp pool DHCPPool import all network 192.168.64.0 255.255.255.0 dns-server 22.214.171.124 126.96.36.199 default-router 192.168.64.253 option 150 ip 10.31.1.107
Note that the DHCP pool is 192.168.64.0/24 and that there are excluded addresses. Note also there is an extra option (here TFTP-server) configured. Everything else should be straight-forward for anybody accustomed with DHCP servers configuration.
This article was first written in April 2005 for the BeezNest technical website (http://glasnost.beeznest.org/articles/224).
To replace a Cisco Remote Access Router, which is only a kind of network serial ports server, you could use a Linux box with Serial to Network Proxy (ser2net).
This article was first written in April 2005 for the BeezNest technical website (http://glasnost.beeznest.org/articles/223).
To manage a bunch of Cisco routers or equipments, a lot of free software have been written over time. Most of them are really useful to ease or improve the management of Cisco material.
Most of the time, they are hopefully not limited to Cisco, but provide support for more.