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BGP Announcement and route selection

Rick Morris
Frequent Contributor
Frequent Contributor

I have a weird BGP issue.

The issue is I see in the routing tables and BGP table the route and where it should be routing to from other locations, however, when I run a traceroute it does not go the direction I intend it to go every time.  All output is below (I am sorry for the length but all details I thought were important.)  Looking for a little help with why this traffic is acting the way it is? 

I need to provide the output in order to understand what I am trying to say.

I am going to provide the route-views output as well as Global Crossing output for comparison.

We have 3 peers.

AS 13490

AS 3112

AS 600 (we have to sessions with this provider)

We prepend our own AS 2025 6 times to our peer AS 13490.  Interestingly after looking at what we announce I do not see the pre-pending at all

route-map AS13490-OUT, permit, sequence 10

  Match clauses:

    ip address prefix-lists: AS2025-DORM-ADV

  Set clauses:

  Policy routing matches: 0 packets, 0 bytes

route-map AS13490-OUT, permit, sequence 20

  Match clauses:

    ip address prefix-lists: AS2025-ADV

  Set clauses:

    as-path prepend 2025 2025 2025 2025 2025 2025

  Policy routing matches: 0 packets, 0 bytes

btsnoc11-br-01#sh ip prefix-list AS2025-ADV

ip prefix-list AS2025-ADV: 4 entries

   seq 5 permit 131.183.0.0/16

   seq 10 permit 136.x.x.x/16

   seq 15 permit 206.x.x.x/24

   seq 20 permit 198.x.x.x/23

btsnoc11-br-01#

router bgp 2025

no synchronization

bgp log-neighbor-changes

network 131.183.0.0

network 136.x.x.x

network 198.x.x.x

network 206.x.x.x

aggregate-address 198.x.x.x 255.255.254.0 summary-only

neighbor 72.x.x.x remote-as 13490

neighbor 72.x.x.x password 7 142201580F11387A303107

neighbor 72.x.x.x ebgp-multihop 10

neighbor 72.x.x.x send-community  <--This will be removed, there is no community string configured for this peer.(cleaning up someone else mess)

neighbor 72.x.x.x soft-reconfiguration inbound

neighbor 72.x.x.x route-map AS13490-IN in

neighbor 72.x.x.x route-map AS13490-OUT out

btsnoc11-br-01#sh ip bgp neigh 72.240.XX.XX adv | i 131.183

*> 131.183.0.0      131.187.253.94           0         32768 i

btsnoc11-br-01#sh ip route 131.183.0.0

Routing entry for 131.183.0.0/16, 3 known subnets

  Variably subnetted with 3 masks

S       131.183.222.0/23 [1/0] via 131.187.253.83

S       131.183.224.0/19 [1/0] via 72.241.59.153

S       131.183.0.0/16 [10/0] via 131.187.253.94

btsnoc11-br-01#sh run | i 131.187.253.94

ip route 131.183.0.0 255.255.0.0 131.187.253.94 10

ip route 136.247.0.0 255.255.0.0 131.187.253.94

ip route 136.247.24.0 255.255.248.0 131.187.253.94

The IP range is 131.183.0.0

route-views>sh ip bgp 131.183.1.253

BGP routing table entry for 131.183.0.0/16, version 2637983298

Paths: (36 available, best #5, table Default-IP-Routing-Table)

  Not advertised to any peer

  3549 3356 13490 2025

    208.51.134.254 (inaccessible) from 208.51.134.254 (67.17.81.150)

      Origin IGP, metric 1, localpref 100, valid, external

  3333 3356 13490 2025

    193.0.0.56 from 193.0.0.56 (193.0.0.56)

      Origin IGP, localpref 100, valid, external

  19214 2828 3356 13490 2025

    208.74.64.40 from 208.74.64.40 (208.74.64.40)

      Origin IGP, localpref 100, valid, external

  701 209 600 2025

    157.130.10.233 from 157.130.10.233 (137.39.3.60)

      Origin IGP, localpref 100, valid, external

  3356 13490 2025

    4.69.184.193 from 4.69.184.193 (4.68.3.50)

      Origin IGP, metric 0, localpref 100, valid, external, best

      Community: 3356:3 3356:22 3356:100 3356:123 3356:575 3356:2035

  2914 3356 13490 2025

    129.250.0.11 from 129.250.0.11 (129.250.0.12)

      Origin IGP, metric 6, localpref 100, valid, external

      Community: 2914:420 2914:1008 2914:2000 2914:3000 65504:3356

  1668 3356 13490 2025

    66.185.128.48 from 66.185.128.48 (66.185.128.48)

      Origin IGP, metric 2, localpref 100, valid, external

  852 174 13490 2025

    154.11.98.225 from 154.11.98.225 (154.11.98.225)

      Origin IGP, metric 0, localpref 100, valid, external

      Community: 852:180

  2828 209 13490 2025

    65.106.7.139 from 65.106.7.139 (66.239.189.139)

      Origin IGP, metric 3, localpref 100, valid, external

  852 174 13490 2025

    154.11.11.113 from 154.11.11.113 (154.11.11.113)

      Origin IGP, metric 0, localpref 100, valid, external

      Community: 852:180

  7500 2516 3356 13490 2025

    202.249.2.86 from 202.249.2.86 (202.249.2.86)

      Origin IGP, localpref 100, valid, external

  1239 3356 13490 2025

    144.228.241.130 from 144.228.241.130 (144.228.241.130)

      Origin IGP, localpref 100, valid, external

  3277 3267 50139 20965 11537 3112 2025

    194.85.102.33 from 194.85.102.33 (194.85.4.4)

      Origin IGP, localpref 100, valid, external

      Community: 3277:3267 3277:65100 3277:65320 3277:65326 3277:65330

  5459 174 13490 2025

    195.66.232.239 from 195.66.232.239 (195.66.232.239)

      Origin IGP, localpref 100, valid, external

      Community: 5459:1 5459:60

  3561 174 13490 2025

    206.24.210.102 from 206.24.210.102 (206.24.210.102)

      Origin IGP, localpref 100, valid, external

  3267 50139 20965 11537 3112 2025

    194.85.40.15 from 194.85.40.15 (193.232.80.7)

      Origin IGP, localpref 100, valid, external

  286 174 13490 2025

    134.222.87.1 from 134.222.87.1 (134.222.85.99)

      Origin IGP, localpref 100, valid, external

      Community: 286:18 286:19 286:28 286:29 286:49 286:800 286:888 286:3031

  3257 174 13490 2025

    89.149.178.10 (inaccessible) from 89.149.178.10 (213.200.87.91)

      Origin IGP, metric 10, localpref 100, valid, external

      Community: 3257:8012 3257:30153 3257:50001 3257:54900 3257:54901

  6453 209 13490 2025

    66.110.0.86 from 66.110.0.86 (66.110.0.86)

      Origin IGP, localpref 100, valid, external

  16150 174 13490 2025

    217.75.96.60 from 217.75.96.60 (217.75.96.60)

      Origin IGP, metric 0, localpref 100, valid, external

      Community: 174:21001 174:22013 16150:63392 16150:65320 16150:65326

  7660 22388 11537 3112 2025

    203.181.248.168 from 203.181.248.168 (203.181.248.168)

      Origin IGP, localpref 100, valid, external

      Community: 7660:10 7660:3000 11537:950 22388:100

  2497 209 13490 2025

    202.232.0.2 from 202.232.0.2 (202.232.0.2)

      Origin IGP, localpref 100, valid, external

  1221 4637 174 13490 2025

    203.62.252.186 from 203.62.252.186 (203.62.252.186)

      Origin IGP, localpref 100, valid, external

  6079 11164 600 2025

    207.172.6.1 from 207.172.6.1 (207.172.6.1)

      Origin IGP, metric 0, localpref 100, valid, external

  812 11164 600 2025

    64.71.255.61 from 64.71.255.61 (64.71.255.61)

      Origin IGP, localpref 100, valid, external

  6079 11164 600 2025

    207.172.6.20 from 207.172.6.20 (207.172.6.20)

      Origin IGP, metric 0, localpref 100, valid, external

  6539 11164 600 2025

    66.59.190.221 from 66.59.190.221 (66.59.190.221)

      Origin IGP, localpref 100, valid, external

  4436 11164 600 2025

    69.31.111.244 from 69.31.111.244 (69.31.111.244)

      Origin IGP, metric 0, localpref 100, valid, external

      Community: 4436:21216 11164:1140 11164:7500 11164:51240 11164:52100 11164:52200

  6939 11164 600 2025

    216.218.252.164 from 216.218.252.164 (216.218.252.164)

      Origin IGP, localpref 100, valid, external

  7018 3356 13490 2025

    12.0.1.63 from 12.0.1.63 (12.0.1.63)

      Origin IGP, localpref 100, valid, external

      Community: 7018:5000

  3303 174 13490 2025

    164.128.32.11 from 164.128.32.11 (138.187.128.158)

      Origin IGP, localpref 100, valid, external

      Community: 3303:1004 3303:1006

  22388 11537 3112 2025

    192.203.116.253 from 192.203.116.253 (192.203.116.253)

      Origin IGP, localpref 100, valid, external

      Community: 11537:950 22388:100

  8075 174 13490 2025

    207.46.32.34 from 207.46.32.34 (207.46.32.34)

      Origin IGP, localpref 100, valid, external

  4826 6939 11164 600 2025

    114.31.199.1 from 114.31.199.1 (114.31.199.1)

      Origin IGP, metric 0, localpref 100, valid, external

  101 101 11537 3112 2025

    209.124.176.223 from 209.124.176.223 (209.124.176.223)

      Origin IGP, localpref 100, valid, external

      Community: 101:20200 101:20210 101:22210 11537:950

      Extended Community: RT:101:22210

  3582 4600 11537 3112 2025

    128.223.253.10 from 128.223.253.10 (128.223.253.10)

      Origin IGP, localpref 100, valid, external

      Community: 3582:567 4600:99

route-views>

Global Crossing Output:

BGP routing table entry for 131.183.0.0/16, version 455605753
Paths: (25 available, best #20, table default)
  Not advertised to any peer
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.ATL1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2454 3549:30840 (North American; United States)
      Originator: loop0.ar4.ATL2.gblx.net, Cluster list: 0.0.0.91
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.ATL1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2454 3549:30840 (North American; United States)
      Originator: loop0.ar4.ATL2.gblx.net, Cluster list: 0.0.0.91
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.JFK1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2355 3549:30840 (North American; United States)
      Originator: loop0.ar5.NYC1.gblx.net, Cluster list: 0.0.0.71
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.NYC1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2355 3549:30840 (North American; United States)
      Originator: loop0.ar5.NYC1.gblx.net, Cluster list: 0.0.0.71
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.CDG2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2623 3549:31250 (Europe; France)
      Originator: loop0.ar3.CDG2.gblx.net, Cluster list: 0.0.0.131
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.CDG2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2623 3549:31250 (Europe; France)
      Originator: loop0.ar3.CDG2.gblx.net, Cluster list: 0.0.0.131
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.AMS2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2682 3549:31528 (Europe; Netherlands)
      Originator: loop0.ar2.AMS1.gblx.net, Cluster list: 0.0.0.121
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.HAM1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2724 3549:31276 (Europe; Germany)
      Originator: loop1.ar4.FRA4.gblx.net, Cluster list: 0.0.0.141
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.AMS2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2682 3549:31528 (Europe; Netherlands)
      Originator: loop0.ar2.AMS1.gblx.net, Cluster list: 0.0.0.121
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.LON3.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2529 3549:31826 (Europe; United Kingdom)
      Originator: loop1.ar9.LON3.gblx.net, Cluster list: 0.0.0.111
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.LON3.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2529 3549:31826 (Europe; United Kingdom)
      Originator: loop1.ar9.LON3.gblx.net, Cluster list: 0.0.0.111
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.FRA4.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2724 3549:31276 (Europe; Germany)
      Originator: loop1.ar4.FRA4.gblx.net, Cluster list: 0.0.0.141
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.SFO1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2145 3549:30840 (North American; United States)
      Originator: loop1.ar5.SJC2.gblx.net, Cluster list: 0.0.0.21
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.LAX1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2022 3549:30840 (North American; United States)
      Originator: loop0.ar2.LAX2.gblx.net, Cluster list: 0.0.0.11
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.MIA1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2474 3549:30840 (North American; United States)
      Originator: loop1.ar4.MIA2.gblx.net, Cluster list: 0.0.0.92
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.PAO2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2145 3549:30840 (North American; United States)
      Originator: loop1.ar5.SJC2.gblx.net, Cluster list: 0.0.0.21
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.PHI1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2407 3549:30840 (North American; United States)
      Originator: ar7.DCA3.gblx.net, Cluster list: 0.0.0.81
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.WDC2.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2407 3549:30840 (North American; United States)
      Originator: ar7.DCA3.gblx.net, Cluster list: 0.0.0.81
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.PHX1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2022 3549:30840 (North American; United States)
      Originator: loop0.ar2.LAX2.gblx.net, Cluster list: 0.0.0.11  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.CHI1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal, best
      Community: 3549:2205 3549:30840 (North American; United States)
      Originator: loop0.ar5.CHI2.gblx.net, Cluster list: 0.0.0.41  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.MIA1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2474 3549:30840 (North American; United States)
      Originator: loop1.ar4.MIA2.gblx.net, Cluster list: 0.0.0.92
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.HOU1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2296 3549:30840 (North American; United States)
      Originator: 67.17.83.0, Cluster list: 0.0.0.61
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.DAL1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2296 3549:30840 (North American; United States)
      Originator: 67.17.83.0, Cluster list: 0.0.0.61
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir2.SEA1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2176 3549:30840 (North American; United States)
      Originator: loop1.ar6.SEA1.gblx.net, Cluster list: 0.0.0.31
  3356 13490 2025, (received & used)
    ge4-12-1000M.ar6.PHX1.gblx.net from loop0.ir1.SEA1.gblx.net
      Origin IGP, metric 100, localpref 201, valid, internal
      Community: 3549:2176 3549:30840 (North American; United States)
      Originator: loop1.ar6.SEA1.gblx.net, Cluster list: 0.0.0.31

XO output:

show ip bgp  131.183.0.0 

BGP routing table entry for 131.183.0.0/16, version 845319987

* * *  Not advertised to any peer

   2828 209 600 2025, (received & used)

     216.156.2.165 from 216.156.2.165 (216.156.2.165)

       Origin IGP, metric 2, localpref 100, valid, external

Traceroutes

rviews

route-views>traceroute 131.183.1.253

Type escape sequence to abort.

Tracing the route to 131.183.1.253

  1 vl-51.uonet1-gw.uoregon.edu (128.223.51.2) [AS 3582] 0 msec 0 msec 0 msec

  2 3.xe-1-3-0.uonet10-gw.uoregon.edu (128.223.3.10) [AS 3582] 0 msec 0 msec 0 msec

  3 vl-105.ge-2-0-0.core0-gw.pdx.oregon-gigapop.net (198.32.165.89) [AS 4600] 0 msec 4 msec 4 msec

  4 vl-101.abilene-losa-gw.oregon-gigapop.net (198.32.165.66) [AS 4600] 24 msec 28 msec 24 msec

  5 xe-0-1-0.0.rtr.hous.net.internet2.edu (64.57.28.97) [AS 11537] 56 msec 60 msec 56 msec

  6 64.57.28.113 [AS 11537] 80 msec 100 msec 120 msec

  7 ae-8.10.rtr.wash.net.internet2.edu (64.57.28.7) [AS 11537] 96 msec 96 msec 92 msec

  8 clevs-r0-xe-1-0-0s359.core.oar.net (192.88.192.137) [AS 3112] 100 msec 104 msec 100 msec

  9 toldb-r9-xe-4-3-0s101.core.oar.net (192.153.39.14) [AS 3112] 128 msec 104 msec 104 msec

10 192.148.242.186 [AS 3112] 104 msec 100 msec 104 msec

11  *  *  *

12  *  *  *

savvis

traceroute to 131.183.1.253 (131.183.1.253), 30 hops max, 40 byte packets
Hop #Router NameIP Address Time
1 ges1.Phoenix3px.savvis.net 208.172.225.10.654 ms
2 acr1-ge-7-2-0.phoenix3px.savvis.net 208.172.227.90.542 ms
3 cr2-pos-0-3-2-2.losangeles.savvis.net 204.70.193.23410.159 ms
4 205.171.1.13 205.171.1.1310.023 ms
5 205.171.32.9 205.171.32.99.853 ms
6 67.14.8.86 67.14.8.8660.318 ms
7 208-47-34-194.dia.static.qwest.net 208.47.34.19466.847 ms
8 core2.buckeyecom.net 72.240.0.20599.830 ms
7 Replies 7

Eugene Khabarov
Rising star
Rising star

Did you cleared bgp session after as-path prepend configuration?

I had asked the people here who set this up and they beleive that it had been done already.  This is something I needed to do for another change I just made.  I will need to schedule that for our maint. window.

I think you don't need to schedule maintaince window to try this one:

clear ip bgp 72.x.x.x soft out

because soft reconfigration outboutn wouldn't lead to downtime.

Please let me know.

Also please be aware of filtering of excessive prepends by upstpream ISPs:

http://wiki.nil.com/Filter_excessively_prepended_BGP_paths

Please rate if it was helpful. "Correct answer" will be also helpful. Thank you.

I had already done that and no change.

I will reply back once changes have been made and bgp session has been hard cleared.

Are you weighting your routes?

There are couple of attributes that is currently configured, local pref and the as prepend.

I am at the point of reconfiguring it all after I have an understanding of what the organization is wanting to accomplish.  This way it will clean up the mess from a previous employee who may or may not have had much understanding of BGP.

Lol yeah, sounds about right

Might be an idea.

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