Cisco IOS configuration examples

While getting ready for my CCNP exams, I purchased quite a few Cisco devices from our national eBay-clone site. While some folks don't really understand, why I don't just use GNS3 and be happy with it, I prefer the hands-on stuff very much. Here's why:

• Things don't go wrong in the simulated stuff as often as they should, to help you learn;
• I have a hardware technician past, so I just like the boxes;
• You don't have to learn memory constraints and upgrades on a simulated router: you just set it to max RAM, best-newest image, boot, done. Real world is not this nice;
• You don't have to recover from a failed IOS upgrade, or do a password recovery;
• And your configs are just too clear.

The last part is one of my problems with official CCNP study materials too: they only config what the chapter wants you to learn. If, for example, you study EIGRP, there won't be serious security configured on the box.

Now this is the part where the second-hand Cisco gear comes in: if you buy it from non-IT people, who didn't use it in their own home lab, chances are, the original config will be there. And that's the way I managed to acquire some live configs from ISPs and corporations. It's not guaranteed that these configs are perfect, but they were running in production networks, every day. So I think they are worth checking out.

Now, before we begin, the usual disclaimer: I deleted sensitive data from the configs, like usernames and passwords, and phone numbers, but not IP addresses (except for AAA servers). Most of these IP addresses are still in use by these organizations, so please be a grow-up, and don't try to hack them. They have some smart guys to track you down, and you don't really want that.

So, let's begin.

For warm-up, a good ol' Cisco 1005 with a serial connection and EIGRP.

Nothing really fancy here, but it gets the job done.

Second, a Cisco 801 with brutal ISDN config, and a kick-ass login banner.

Isn't that just beautiful?

Highlights include:

interface Dialer2

ip unnumbered Ethernet0

interface Dialer10

ip address 194.48.122.236 255.255.255.0

interface Dialer61

ip unnumbered Ethernet0

interface Dialer99

ip address negotiated

Next, a Cisco 3620 as a terminal server, but I'm not sure about the hardware config.

This was used by an ISP.

Highlights include:

interface Virtual-Template1

interface Group-Async1

A Cisco 2500 in a private WAN environment, with EIGRP, serial with ISDN backup.

A Cisco 1601, Frame relay and ISDN backup.

Highlights include:

priority-list 1 protocol ip high list 150

priority-list 1 protocol ip medium list 151

priority-list 1 protocol ip normal list 152

priority-list 1 protocol ip low list 153

And finally, a nice MC3810 config, after migrating to PPP from frame relay, with E&M voice ports. Used by another Telco/ISP.

Highlights include:

interface Multilink1

voice-port 1/1

dial-peer voice 1 vofr

dial-peer voice 2 pots

And so, this is the current state of my little collection. If you want to share your own stuff, I'm very much interested.

The ultimate console cable

Forget my previous post on the Foundry console cable...

This is the stuff, that gets everything done:

http://routerjockey.com/2011/06/17/my-toolbag/

CCNP home lab serial connections: T1 is the way to go!

As I'm building my home lab for the ROUTE exam, I find the DB60 DTE-DCE cables increasingly problematic, because:

• they cost money,
• they are bulky,
• they are as flexible as a flagpole.

After playing around with different back-to-back connections, eBay provided the ultimate solution: WIC-1DSU-T1 cards.

They are cheaper than WIC-1T and WIC-2T cards, and use regular UTP cables (not with ethernet pinout, mind you!) for connection. Everything I need for a neat, organized rack. Only downside: they need modular routers, and can't be used with the built-in interfaces of my 1005, 1605R and 2500 series boxes.

The command to remember:

service-module t1 clock source {line | internal}

Default is line, so set one end of the link to internal.

Foundry/Brocade console cable

A few months ago I managed to buy a Foundry FWS24 switch. It comes with a DB9 serial port, but it does not work with a standard rollover DB9-RJ45 cable + RJ45-DB9 adapter combo.

Turns out it needs a straight serial cable instead of a rollover, but the built-in DB9 port is male, and I don't have female-female straight cables on hand.

At first I did an ugly hack with a DB9-DB25 modem cable, but I didn't like it very much, so I sacrificed one of my baby-blue Cisco cables, cut off the RJ45 plug on the end, and crimped a new one upside-down on it (black wire to pin 8), making it a straight cable. Using that cable and a standard Cisco DB9-RJ45 adapter (74-0495-01), the Foundry box works like a charm.

Linux bridge STP long path cost (802.1t-2001)

A few years ago, we had to implement STP on Linux boxes, using the long path cost standard. If changing the cost values from userspace is not really your thing, here's a patched br_if.c source (mind you, it's for an old kernel version, probably 2.6.17 or something).

Edit: for those who are interested in the actual numbers, not the Linux code:

http://en.wikipedia.org/wiki/Spanning_tree_protocol#Data_rate_and_STP_path_cost