BGP:Using route-map to set Local Preference and metric?

[blackhat2020]

Hi every one.I want to know that can i use a route map and set local preference in it to changing Local Preference when im SENDING(out bond) traffic to a neighbor or i can use this kind of route map on INBOND because in a situation i tried to apply a route map to a neighbor on outbond direction but in neighbor i check the  routes and it did not recieved the route with new local Preference? am i right our im doing something wrong if im right i think i should use as prepending ?

2- when using MED does it apply only with eBGP peers? because i tried to change the metric when sending updates to my iBGP peer but it didnt work(with route map) so i thought that it works only when challenging with eBGP peer?is this true

thanks.

[Jon Marshall]

Local prefernce is used with an AS to influence the exit path for traffic. So because it is used within an AS you cannot influence another ASs eBGP routers with local preference. Local preference is sent throughout the AS using IGBP.

MED is used to influence the entry path for traffic from a remote AS. So it doesn't make any sense for the MED to passed within the same AS using IBGP.

Jon

[blackhat2020]

Thanks Jon.about the MED you are right but what about the Local Preference within the AS i mean if i want to chage the routes LP that im Advertising to my iBGP peer can i use route-map in out direction(to my peer) to set the Local Preference? because in iBGP peering when i get updates i can use route-map in IN direction from y peer to change the LP when the routes are coming from my peer but i tried it to change the LP another time when I AM sending updates to another peer and it didnt worked.

[KARUPPUCHAMY MALAIYANDI]

Hi,

Local preference is applicable within the AS.Either we can change the LP value for the outbound updates to the neighbor or inbound updates from the neighbor.

Take example that R1 and R2 are configured as iBGP neighbors.Now if R2 want the routes from R1 with high local preference then we can do the following methods

1.write a route map in R1 and match the routing updates then increase the LP value after that apply this route map into neighbor R2 as outbound

2.write a route map in R2 and match the routing updates then increase the LP value after that apply this route map into neighbor R1 as inbound.

I hope it should work,

Thanks & Regards

Karuppu

[william.lipsit]

Some service providers allow you to send them a community string and they will set local preference on their network for your routes. Contact your Service Provider to see their policy.

Here is Sprint's Inofrmation:

LOCAL PREFERENCE

You can control the local preference for your announcements on the Sprint router using a community string which you may pass to Sprint in your BGP session. The following table lists the community strings and the corresponding local preference that Sprint will set in the network. Remember that community strings are not exported by default, so be sure to add whatever export command is neccessary for your router.

---

String	Resulting Local Pref
1239:70	70
1239:80	80
1239:90	90
1239:100	100
1239:110	110

Here is the link from Sprint:

https://www.sprint.net/index.php?p=policy_bgp