BGP Community String for Level3(Legacy WilTel) AS7911

   March 4, 2007  Leave a comment

Attention

This BGP Community string information might be outdated. Please contact Level3(Legacy WilTel)  AS7911 to get more recent one. This BGP communites is ONLY for the customer who has BGP with Level3(Legacy WilTel)  AS7911. www.ipbalance.com is not maintaining this BGP Community string.

 

Received (Internal) BGP Community String


Wiltel Level 3
7911:7 — 3356:123 – Customer Routes
7911:2 — 3356:666 – Peer Routes
7911:3 — none – Transit Routes

Local Pref Adjustments:
Wiltel Level 3
7911:90 — 3356:70 – Below peer (applicable for both 7911 & 3356)
7911:100 — 3356:80 – Equal peer (applicable for 7911, but below peer for 3356)
7911:110 — 3356:90 – Higher than peer, lower than customer default (applicable for both 7911 & 3356)


** Level 3 does not offer a local preference setting equal to peer

Customer Setable BGP Community String


Announcement Adjustments Wiltel:
Start with 7911:2000
Add the following for action to take:
0 – Do not adverstise
100 – Prepend once
200 – Prepend twice
300 – Prepend thrice


Add the following for peer to take this action on:
11 – AS7018
12 – AS3561
13 – AS6461
14 – AS4544 **
15 – AS3549
16 – AS3356 **
17 – AS209
18 – AS1239
19 – AS2914
20 – AS701
21 – AS19548 **
22 – AS174
23 – AS22273 **

** This network is not a peer of the Level 3 network therefore this action is not available


EXAMPLE(s): 7911:2128 would prepend 7911 once towards 1239 (Sprint)
7911:2019 would surpress announcement towards 2914 (NTT/Verio)

General Peer Route Suppression:
Wiltel Level(3)
7911:999 — 65000:0 – announce to customers but not to peers

General "no-export" Surpression:
WilTel Level(3)
7911:888 — no-export

 

 

Applying BGP Community string with sample configuration

1. Get the latest BGP community string from your ISP/upstream provider or check www.ShowipBGP.com.

2. Pick the best BGP community string for your traffic shaping plan (mainly incoming traffic). Most of ISPs are providing BGP community string with local preference and AS prepending option. Cannot tell which one is better than the other. It will depend on your global traffic shaping plan.

3. Follow the below commands ( Cisco only )

The below Sample configuration will tag the 10.0.0.0/24 route with [ISP AS]:120 or [ISP AS]:3 and will not tag any other routes.


router#config t
router(config)#ip bgp-community new-format
router(config)#access-list 10 permit 10.0.0.0 0.0.0.255
router(config)#access-list 10 deny any

router(config)#route-map [to-ISP] permit 10
router(config-route-map)#match ip address 10
router(config-route-map)#set community [ISP AS]:120 <—- using Local Preference

or

router(config-route-map)#set community [ISP AS]:3 <——- using AS prepending
router(config-route-map)#route-map [to-ISP] permit 20
router(config-route-map)#exit

router(config)#router bgp [xxxx] <——————————- xxxx = customer’s ASN
router(config-router)#neighbor x.x.x.x send-community
router(config-router)#neighbor x.x.x.x route-map [to-ISP] out
router(config-router)#exit
router(config)#exit
router#copy running-config startup-config


4. And then, go to www.RouteServer.org and pick one of route server on the map to see your announcement. If you are using AS prepending option, you will see your AS prepends on route servers. Sometime you might not see your route with particular ISP path.
In most of case it might not be any routing problem, just the route path was dropped at somewhere by BGP best path selection scheme. Try Oregon route server, if you can see your route. The Oregon route server is providing many possible and available paths between BGP speakers and neighbors.
If you don’t see your route on there? check other route servers and also check your
BGP configuration. You might need to contact your upstream provider to check what they are learning BGP route from you.

 

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