Troubleshooting. Vecinos BGP (IBGP o EBGP) no se conectan a través de la ruta por defecto.

Un gran amigo me llama para hacerme una pregunta de BGP. Al ver la situación pensé que no había problema en la configuración que me dice, pero menciona que no levanta la sesión. Me pareció raro, por lo que me adentre al problema:

Se coloca un escenario para que se conecten a través de BGP, pero no funciona. La configuración y el diagrama es como sigue:

BGP_Default_Route.JPG

Al parecer todo parece estar en orden e incluso se puede realizar ping entre ellos, pero la sesión BGP no levanta:

R1#ping 2.2.2.2 source loopback0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/44/80 ms
R1#
R1#show ip bgp summar
BGP router identifier 1.1.1.1, local AS number 65001
BGP table version is 1, main routing table version 1

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
2.2.2.2         4 65001       2       2        0    0    0 never    Active
R1#

Cuando se activa el comando debug ip bgp, se observa lo siguiente:

R1#
*Mar  1 00:47:41.587: BGP: 2.2.2.2 active open failed - no route to peer, open active delayed 27980ms (35000ms max, 28% jitter)
R1

Solución:

Se debe agregar la ruta en alguno de los dos puntos. El problema es que BGP no utiliza las rutas por defecto para su inicio de conexión BGP.

R1#config t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#ip route 2.2.2.2 255.255.255.255 12.12.12.2
R1(config)#end
R1#
*Mar  1 00:48:31.459: %SYS-5-CONFIG_I: Configured from console by console
R1#
*Mar  1 00:48:36.307: BGP: 2.2.2.2 open active, local address 1.1.1.1
*Mar  1 00:48:36.427: BGP: 2.2.2.2 went from Active to OpenSent
*Mar  1 00:48:36.427: BGP: 2.2.2.2 sending OPEN, version 4, my as: 65001, holdtime 180 seconds
*Mar  1 00:48:36.431: BGP: 2.2.2.2 send message type 1, length (incl. header) 45
*Mar  1 00:48:36.607: BGP: 2.2.2.2 rcv message type 1, length (excl. header) 26
*Mar  1 00:48:36.607: BGP: 2.2.2.2 rcv OPEN, version 4, holdtime 180 seconds
*Mar  1 00:48:36.607: BGP: 2.2.2.2 rcv OPEN w/ OPTION parameter len: 16
*Mar  1 00:48:36.611: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 6
*Mar  1 00:48:36.611: BGP: 2.2.2.2 OPEN has CAPABILITY code: 1, length 4
*Mar  1 00:48:36.611: BGP: 2.2.2.2 OPEN has MP_EXT CAP for afi/safi: 1/1
*Mar  1 00:48:36.611: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
*Mar  1 00:48:36.611: BGP: 2.2.2.2 OPEN has CAPABILITY code: 128, length 0
*Mar  1 00:48:36.615: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability(old) for all address-families
*Mar  1 00:48:36.615: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2 (Capability) len 2
*Mar  1 00:48:36.615: BGP: 2.2.2.2 OPEN has CAPABILITY code: 2, length 0
*Mar  1 00:48:36.615: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability(new) for all address-families 
BGP: 2.2.2.2 rcvd OPEN w/ remote AS 65001
*Mar  1 00:48:36.615: BGP: 2.2.2.2 went from OpenSent to OpenConfirm
*Mar  1 00:48:36.619: BGP: 2.2.2.2 went from OpenConfirm to Established
*Mar  1 00:48:36.619: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up 
R1#
R1#show ip bgp summ
BGP router identifier 1.1.1.1, local AS number 65001
BGP table version is 1, main routing table version 1

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
2.2.2.2         4 65001       6       6        1    0    0 00:00:55        0
R1#

Este escenario sucede en iBGP y eBGP. Este problema ya fue documentado, por lo que nos hubieramos ahorrado un poco de tiempo si lo hubiera leido anteriormente :p :
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093fb8.shtml#noroutes

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License