Route map explaination

[Steven Williams]

                   Can anyone describe a route map in some beginners terms? What is, what it does, and why we use it, and maybe a simple common route map example. I am new to BGP so it is a lot to grasp at one time.

Thanks.

[Firuz Azimov · Accepted solution]

Hello. I  remember from CBT Nuggest. That route-map like programm script. It has variety functions

For Example

route-map test permit 10

match ip address 100

set metric 100

All routes matched access-list 100 will have metric 100

Routes that do not match acl 100 will be blocked, because like access-list route-map has rule Implicit deny

So If you do not want to block other routes need to add  this statement to above route-map test

route-map test permit 50

If route-map has no match statement it means match-all

There many documents in cisco.com about route-map

Hope this help

[Vivek Ganapathi]

Hi Steven,

Let me explain you this in my way. Route-maps is basically a function to customize traffic management beyond the boundaries of the routing table. This is a feature which can be used with any routing protocol like EIGRP, OSPF, BGP etc etc. Examples would be achieve a policy based routing (influencing specific hosts / subnets to take certain path), for traffic engineering to influence outbound traffic (Local preference in BGP), to influence inbound traffic (MED in BGP). Apply route-tags etc etc. Overall a very useful function. 

Assume you have a corporate office & the company name is XYZ. Recently, company XYZ took over a company ABC & the employees are now sitting within the same corporate office as of XYZ.

XYZ & ABC have seperate internet connection. Now till the complete acquisition process is completed, you have been tasked to implement a solution which requires to segregate XYZ & ABC internet traffic. So, how do you do this? What would be a way to achieve this. We can do something called Policy Based Routing (PBR). We determine based on the source IP address / subnet, where to deliver the traffic to. PBR is accomplished using route-map function.

Above is one of an example. Another one would be, your office has two internet links. You would need to utilize both links (load share). You may use to send internet bound traffic out on Link A, but the return traffic on Link B. This is again achieved using a route-map function with different BGP features like AS Path prepending, MED etc.

Hope this helps.

Regards

Vivek

[Giuseppe Larosa]

Hello Steven,

route-maps are special composite filters that allow to select routes to be sent to a neighbor or received by a neighbor and at the same time they can modify all BGP attributes of the selected IP prefix.

The route-map allows use different match conditions that can match on:

IP prefixes with access-lists or IP prefix-lists.

BGP attributes:

extended filtering on AS path attribute seen as a string like "1000 2000 55 i" using regular expressions

match on local preference or MED ( metric)

match on BGP community and so on.

all BGP attributes can also be manipulated

Hope to help

Giuseppe