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Re: RADB entry
From: Courtney Smith <courtneysmith () comcast net>
Date: Tue, 11 Dec 2012 21:09:40 -0500

Chuck,

If you look at the communities on 68.115.27.0/24 you will see 7018:5000.  That community means AS209 is a AT&T peering 
partner.  

route-server>sh ip bgp 68.115.217.201
BGP routing table entry for 68.115.217.0/24, version 13683280
Paths: (18 available, best #7, table Default-IP-Routing-Table)
 Not advertised to any peer
...
 7018 209 20115, (aggregated by 20115 96.34.212.29), (received & used)
   12.123.1.236 from 12.123.1.236 (12.123.1.236)
     Origin IGP, localpref 100, valid, external, atomic-aggregate, best
     Community: 7018:5000 7018:37232



Now if you look at results for 75.77.38.0/23 you will see 7018:2000.  That would mean AS7029 is an AT&T customer.  

route-server>sh ip bgp 75.77.38.0
BGP routing table entry for 75.77.38.0/23, version 26960376
Paths: (19 available, best #7, table Default-IP-Routing-Table)
 Not advertised to any peer
7018 7029 26296 26296 26296, (received & used)
   12.123.1.236 from 12.123.1.236 (12.123.1.236)
     Origin IGP, localpref 100, valid, external, best
     Community: 7018:2000 7018:34011



In AT&T's network, I believe they apply local pref 80 for peer routes and local pref 100 for customer routes.  Ignore 
the local pref values you see on the route server.

Let's look at what appears to be going on.  Per your earlier post, you verified Charter(AS20115) has the prefix.  
Charter does not appear to have a interconnect with AT&T(7018) so they send to Centurlink/Qwest(AS209).  We see 
Centurylink(AS209) accepts per their looking glass at https://kai04.centurylink.com/PtapRpts/Public/BackboneReport.aspx.


BGP routing table entry for 75.77.38.0/23
    20115 26296
    Nexthop 205.171.0.93 (via 207.109.19.150) from chi-core-01 (205.171.0.144)
    Origin IGP, metric 0, localpref 100, internal, valid
    Last update: 13:30:09 ago
    Communities: 209:209 209:14520 20115:3200 20115:63004
    Originator Id: 205.171.0.93
    Cluster ID List: 207.109.19.145 205.171.0.149


Now Centurylink(AS209), sends the /23 to their peer AT&T(AS7018).  AT&T accepts the /23 from Centurylink.  Since 
Centurylink is their peer, AT&T assigns local pref 80.  That's lower than the 100 assigned to the Windstream.  Highest 
local pref wins.  Your prepends are never part of the decision.  So AT&T continues to pref the path via their customer 
Windstream(AS7029).  

I suspect this is really your problem instead of route registry data.  Hopefully, Windstream offers their customers 
some BGP communities to allow traffic engineering.  

Finally, the WISP has a AS number from ARIN, they should be able to create their own maintainer on rr.arin.net.  The 
RADB fee might be a little much for your WISP.  https://www.arin.net/resources/routing/

Make sense?

 
On Dec 11, 2012, at 7:07 PM, Chuck Church wrote:

Courtney,

      This is from the AT&T 7018 route server.  The first one is our WAN
IP address, part of our ISP's ASN.  The second one is our own /23.  The
first one goes through Century Link, then Charter.  The second one I would
think would take same path, with one additional AS (our own).  But that one
isn't present at AT&T.  Level 3 shows the same thing.  Century Link
themselves see our /23 through Charter...

route-server>sh ip bgp 68.115.217.201
BGP routing table entry for 68.115.217.0/24, version 13683280
Paths: (18 available, best #7, table Default-IP-Routing-Table)
 Not advertised to any peer
...
 7018 209 20115, (aggregated by 20115 96.34.212.29), (received & used)
   12.123.1.236 from 12.123.1.236 (12.123.1.236)
     Origin IGP, localpref 100, valid, external, atomic-aggregate, best
     Community: 7018:5000 7018:37232

route-server>sh ip bgp 75.77.38.0
BGP routing table entry for 75.77.38.0/23, version 26960376
Paths: (19 available, best #7, table Default-IP-Routing-Table)
 Not advertised to any peer
7018 7029 26296 26296 26296, (received & used)
   12.123.1.236 from 12.123.1.236 (12.123.1.236)
     Origin IGP, localpref 100, valid, external, best
     Community: 7018:2000 7018:34011


Thanks,

Chuck


-----Original Message-----
From: Courtney Smith [mailto:courtneysmith () comcast net] 
Sent: Tuesday, December 11, 2012 5:38 PM
To: nanog () nanog org
Subject: Re: RADB entry



Anyone,



              Hopefully this is a simple question about RADB.  I'm 
supporting a small wireless ISP, they just recently added a second 
upstream connection - Charter (AS 20115).  The IP space was originally 
issued by the other upstream Windstream (AS 7029).  Looking at a few 
resources such as the bgp.he.net to see who peers with who and looking 
glasses, it seems that not all of AS 20115 peers are accepting our 
prefix.  AT&T is an example - AS7018.  In one case, it's an upstream 2 
levels up - Century Link accepts from Charter, but Level 3 doesn't 
accept it from Century Link.  Charter uses RADB.  The entry for the prefix
looks like this:




What makes you think Level3 is not accepting from CenturyLink?  I suspect
Century Link may be a peer of Level3 instead of a customer.   Windstream
appears to be a customer of Level3.  Level3 will put a higher local pref on
customer routes.



Courtney Smith
courtneysmith () comcast net

()  ascii ribbon campaign - against html e-mail 
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Courtney Smith
courtneysmith () comcast net

()  ascii ribbon campaign - against html e-mail 
/\  www.asciiribbon.org   - against proprietary attachments




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