Friday, February 26, 2010

Advertise maps in BGP

A recent discussion on groupstudy pushed me into labbing BGP again.
In BGP, Advertise maps are used for two functions;
1. Conditional Advertisement
2. Route aggregation.

In conditional advertisement, Advertise maps are with an EXIST-MAP (or NON-EXIST map) to perform conditonal advertisement. Here the advertise-map specifies a route-map that matches the prefixes that would be advertised ONLY if the prefixes in the EXIST-MAP exist in the routing table.

The syntax is "neighbor ip-address advertise-map map-name {exist-map|non-exist} map-name"

The other use of advertise-maps is in specifying what attribute would be carried along in the as-set attributes of an aggregate during summarization.

Assume we have R1, R2,R3 and R4 in AS 1, 2,3 and 4 respectively
R1 -- R4 --- R3

R1, R2, and R3 advertise 150.1.x.0/24 into bgp where x is the router number.

R4 aggregates the routes to 150.1..0.0/16 with as-set attribute.
By default, none of the routers get the update anymore since their
individual routes are a part of the summary.

Using advertise map, we want to make R1 and R3 get the summary; so we only advertise the attributes of the prefix form R2 with the summary.

Using as path access-lists and route-maps on R4 we have,

ip as-path access-list 1 permit ^2$
route-map adv permit 10
match as-path 1

router bgp 4
aggregate-address as-set summary-only advertise-map adv

Now, R1 and R3 get the summary, R2 doesn't because its AS number is carried along with the summary

R1(config-router)#do sh ip bg | i
*> 0 0 4 2 i

R2(config-router)#do sh ip bg | i

Ok. That's it for now. Back to security :-) I was trying to look into NAC with the CTA and CSA. Fun stuff :D


Friday, February 5, 2010

Death of Dynamips...or NOT?

Hi All,

Cisco has introduces software licensing with the IOS 15.0
My first reaction was to mourn the exiit of my faithful friend...DYNAMIPS.

But on a closer look, the IOS licensing DOES NOT directly affect dynamips.

"Cisco Software Activation is a simplified approach to software deployment and management, and is implemented on Cisco Catalyst 3750-E and 3560-E Switches and Cisco Integrated Services Routers Generation 2"

Dynamips CANNOT emulate the devices with licenses yet.

The Licensing hasn't been implemented on the 7200s yet so we can still run the 15.0 on the 7200 routers.

Thanks to Ivan of "Cisco IOS Hints and Tricks" for pointing this out.

I guess we can still have fun studying afterall :-)

Tuesday, February 2, 2010

Creating a Loopback Adapter on Windows 7

The Microsoft Loopback Adapter is a very useful tool for setting up networks with dynamips/gns3 when you need to connect the emulated network to the life system.
Instances include; setting up a terminal Server, connecting to a AAA server, using a VPN Client etc.

With Windows XP/Vista, creating a Loopback Adapter is Pretty Easy;

1. Go to control Panel
2. Click Add Hardware
3. Select Install Hardware from list,
4. Select Network Adapters
5. Select Microsoft as the Manufacturer
6. Select Microsoft loopback Adapter
7. Click Next and Install...
With Windows 7, there is a slight problem; "Add Hardware" is no longer in the Control Panel.
It is now a hidden feature that has to be run by an adminstrator from command prompt.

To get to the Add Hardware program;

1. Run command prompt as Administrator.
2. From command prompt, Run "hdwwiz.exe"

To install the Loopback Adapter, Follow steps 3 through 7 above.

Have fun studying.