Pruebas con anuncios BGP inter-AS e intra-AS
Fecha: 4 y 5 de mayo
del 2023
Escenario
Este laboratorio es una continuación del
escenario anterior
y se centra en las actualizaciones entre peers BGP.
Por un lado, peers en diferentes AS (sistemas
autónomos), y por otro, peers dentro de un mismo AS que reciben
actualizaciones externas y cómo se comporta el
atributo next-hop.
También se analiza la búsqueda recursiva en la
tabla de enrutamiento para poder alcanzar un destino determinado.
Los mensajes UPDATE los generamos agregando el
vecino BGP-3 dentro del AS 65531 con las redes 181.0.4.0 a 181.0.9.0/24,
este publicará hacia BGP-1 dichas redes, y BGP-1
las publicará hacia BGP-2 fuera del AS.
También BGP-1 informará a BGP-3 sobre las redes
181.0.1.0 a 181.0.3.0/24 publicadas por el mismo, y las redes publicadas por
BGP-2 que pertenecen al AS 65530, que son
200.0.1.0 a 200.0.3.0/24.
1.- Verificación inicial:
1.1.- De peer BGP en BGP-1:
BGP-1#sh ip bgp neighbors
BGP neighbor is 190.0.0.2,
remote AS 65530, external link
BGP version 4, remote router ID
190.0.0.2
BGP state = Established, up for 00:10:16
Last read 00:00:19, last write
00:00:18, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and
received(old & new)
Address family IPv4 Unicast:
advertised and received
---resumido/omitido---
BGP-1#
1.2.- De rutas en BGP-1:
BGP-1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP
external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type
1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1,
E2 - OSPF external type 2
i - IS-IS, su - IS-IS
summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * -
candidate default, U - per-user static route
o - ODR, P - periodic
downloaded static route
Gateway of last resort is not set
B 200.0.1.0/24 [20/0] via 190.0.0.2, 00:03:25
(ruta aprendida desde BGP-2)
190.0.0.0/24 is subnetted, 1 subnets
C 190.0.0.0 is directly
connected, FastEthernet0/0
B 200.0.2.0/24 [20/0] via 190.0.0.2, 00:03:25
(ruta aprendida desde BGP-2)
B 200.0.3.0/24 [20/0] via 190.0.0.2, 00:03:25
(ruta aprendida desde BGP-2)
181.0.0.0/24 is subnetted, 3 subnets
C 181.0.1.0 is directly
connected, FastEthernet0/1.1811
C 181.0.3.0 is directly
connected, FastEthernet0/1.1813
C 181.0.2.0 is directly
connected, FastEthernet0/1.1812
BGP-1#
1.3.- De rutas en BGP-2:
[admin@BGP-2] > ip route
print
Flags: X - disabled, A -
active, D - dynamic,
C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
0 ADb 181.0.1.0/24 190.0.0.1 20 (ruta aprendida desde BGP-1)
1 ADb
181.0.2.0/24 190.0.0.1 20 (ruta aprendida desde BGP-1)
2 ADb
181.0.3.0/24 190.0.0.1 20 (ruta aprendida desde BGP-1)
3 ADC
190.0.0.0/24 190.0.0.2 ether1 0
4 ADC 200.0.1.0/24 200.0.1.1 vlan201 0
5 ADC 200.0.2.0/24 200.0.2.1 vlan202 0
6 ADC 200.0.3.0/24 200.0.3.1 vlan203 0
[admin@BGP-2] >
2.- Se conecta el segmento
iBGP 181.0.0.0/24:
Este segmento actuará como backbone entre ambos
peers del AS 65531
2.1.- Declaramos el peer en
BGP-1:
BGP-1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
BGP-1(config)#router bgp
65531
BGP-1(config-router)#neighbor
181.0.0.2 remote-as 65531
BGP-1(config-router)#end
BGP-1#
2.2.- Declaramos el peer en
BGP-2:
BGP-3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
BGP-3(config)#router bgp
65531
BGP-3(config-router)#neighbor
181.0.0.1 remote-as 65531
BGP-3(config-router)#end
BGP-3#
*May 4 18:00:41.784:
%BGP-5-ADJCHANGE: neighbor 181.0.0.1 Up
BGP-3#
2.3.- Verificamos vecindad en BGP-3:
BGP-3#sh ip bgp neighbors
BGP neighbor is 181.0.0.1,
remote AS 65531, internal link (router BGP-1)
BGP version 4, remote router ID
190.0.0.1
BGP state = Established, up for 00:06:08
Last read 00:00:08, last write
00:00:23, hold time is 180, keepalive interval is 60 seconds
Neighbor sessions:
1 active, is not multisession
capable (disabled)
Neighbor capabilities:
Route refresh: advertised and
received(new)
Four-octets ASN Capability:
advertised
Address family IPv4 Unicast:
advertised and received
Enhanced Refresh
Capability: advertised
---resumido/omitido---
BGP-3#
2.4.- Verificamos vecindad
en BGP-1:
BGP-1#sh ip bgp neighbors
BGP neighbor is 181.0.0.2,
remote AS 65531, internal link (router BGP-3)
BGP version 4, remote router ID
181.0.0.2
BGP state = Established, up for 00:07:17
Last read 00:00:41, last write
00:00:17, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and
received(old & new)
Address family IPv4 Unicast:
advertised and received
---resumido/omitido---
BGP neighbor is 190.0.0.2,
remote AS 65530, external link (router BGP-2)
BGP version 4, remote router ID
190.0.0.2
BGP state = Established, up for 00:20:19
Last read 00:00:29, last write
00:00:18, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and
received(old & new)
Address family IPv4 Unicast:
advertised and received
---resumido/omitido---
BGP-1#
3.- Se agregan nuevas redes
en el AS 65531:
BGP-3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
BGP-3(config)#router bgp
65531
BGP-3(config-router)#network
181.0.4.0 mask 255.255.255.0
BGP-3(config-router)#network
181.0.5.0 mask 255.255.255.0
BGP-3(config-router)#network
181.0.6.0 mask 255.255.255.0
BGP-3(config-router)#network
181.0.7.0 mask 255.255.255.0
BGP-3(config-router)#network
181.0.8.0 mask 255.255.255.0
BGP-3(config-router)#network
181.0.9.0 mask 255.255.255.0
BGP-3(config-router)#end
BGP-3#
4.- Verificamos:
4.1.- En BGP-1:
BGP-1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP
external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type
1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1,
E2 - OSPF external type 2
i - IS-IS, su - IS-IS
summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * -
candidate default, U - per-user static route
o - ODR, P - periodic
downloaded static route
Gateway of last resort is not set
B 200.0.1.0/24 [20/0] via 190.0.0.2, 00:22:11
(ruta aprendida desde BGP-2)
190.0.0.0/24 is subnetted, 1 subnets
C 190.0.0.0 is directly
connected, FastEthernet0/0
B 200.0.2.0/24 [20/0] via 190.0.0.2, 00:22:11
(ruta aprendida desde BGP-2)
B 200.0.3.0/24 [20/0] via 190.0.0.2, 00:22:11
(ruta aprendida desde BGP-2)
181.0.0.0/24 is subnetted, 10 subnets
B 181.0.5.0 [200/0] via 181.0.0.2,
00:01:31 (ruta aprendida
desde BGP-3)
B 181.0.4.0 [200/0] via 181.0.0.2,
00:01:31 (ruta aprendida
desde BGP-3)
B 181.0.7.0 [200/0] via 181.0.0.2,
00:01:31 (ruta aprendida
desde BGP-3)
B 181.0.6.0 [200/0] via 181.0.0.2,
00:01:31 (ruta aprendida
desde BGP-3)
C 181.0.1.0 is directly
connected, FastEthernet0/1.1811
C 181.0.0.0 is directly
connected, FastEthernet0/1.1810
C 181.0.3.0 is directly
connected, FastEthernet0/1.1813
C 181.0.2.0 is directly
connected, FastEthernet0/1.1812
B 181.0.9.0 [200/0] via 181.0.0.2,
00:01:33 (ruta aprendida
desde BGP-3)
B 181.0.8.0 [200/0] via 181.0.0.2,
00:01:33 (ruta aprendida
desde BGP-3)
BGP-1#
4.2.- En BGP-2:
[admin@BGP-2] > ip route
print
Flags: X - disabled, A - active, D - dynamic,
C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
0 ADb 181.0.1.0/24
190.0.0.1 20 (ruta publicada por BGP-1)
1 ADb
181.0.2.0/24
190.0.0.1 20 (ruta publicada por BGP-1)
2 ADb
181.0.3.0/24
190.0.0.1 20 (ruta publicada por BGP-1)
3 ADb 181.0.4.0/24
190.0.0.1 20 (ruta ruta publicada por BGP-3
pero aprendida desde BGP-1)
4 ADb
181.0.5.0/24
190.0.0.1 20 (ruta ruta publicada por BGP-3
pero aprendida desde BGP-1)
5 ADb
181.0.6.0/24
190.0.0.1 20 (ruta ruta publicada por BGP-3
pero aprendida desde BGP-1)
6 ADb
181.0.7.0/24
190.0.0.1 20 (ruta ruta publicada por BGP-3
pero aprendida desde BGP-1)
7 ADb
181.0.8.0/24
190.0.0.1 20 (ruta ruta publicada por BGP-3
pero aprendida desde BGP-1)
8 ADb
181.0.9.0/24 190.0.0.1 20 (ruta ruta publicada por BGP-3 pero aprendida desde
BGP-1)
9 ADC
190.0.0.0/24 190.0.0.2 ether1 0
10 ADC 200.0.1.0/24 200.0.1.1 vlan201 0
11 ADC 200.0.2.0/24 200.0.2.1 vlan202 0
12 ADC
200.0.3.0/24 200.0.3.1 vlan203 0
[admin@BGP-2] >
4.3.- En BGP-3:
Nos encontramos con que no “aparecen” en la tabla
las rutas publicadas por BGP-2 (AS 65530).
BGP-3#sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP
external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type
1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF
external type 2
i - IS-IS, su - IS-IS
summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * -
candidate default, U - per-user static route
o - ODR, P - periodic
downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % -
next hop override
Gateway of last resort is not set
181.0.0.0/16 is variably
subnetted, 17 subnets, 2 masks
C 181.0.0.0/24 is directly
connected, Vlan1810
L
181.0.0.2/32 is directly connected, Vlan1810
B 181.0.1.0/24 [200/0] via 181.0.0.1,
00:14:59 (ruta publicada por
BGP-1)
B 181.0.2.0/24 [200/0] via 181.0.0.1,
00:14:59 (ruta publicada por
BGP-1)
B 181.0.3.0/24 [200/0] via 181.0.0.1,
00:14:59 (ruta publicada por
BGP-1)
C 181.0.4.0/24 is directly
connected, Vlan1814
L 181.0.4.1/32 is directly
connected, Vlan1814
C 181.0.5.0/24 is directly
connected, Vlan1815
L 181.0.5.1/32 is directly connected, Vlan1815
C 181.0.6.0/24 is directly
connected, Vlan1816
L 181.0.6.1/32 is directly
connected, Vlan1816
C 181.0.7.0/24 is directly
connected, Vlan1817
L 181.0.7.1/32 is directly
connected, Vlan1817
C 181.0.8.0/24 is directly
connected, Vlan1818
L 181.0.8.1/32 is directly
connected, Vlan1818
C 181.0.9.0/24 is directly
connected, Vlan1819
L 181.0.9.1/32 is directly
connected, Vlan1819
BGP-3#
5.- Verificamos en la tabla
de BGP-3:
Podemos ver que las rutas efectivamente se
encuentran en la tabla BGP, pero con el next-hop real del router BGP-2,
que no es vecino de BGP-3 sino que está a un
salto de distancia, vía el router BGP-1.
BGP-3#sh ip bgp
BGP table version is 16, local router ID is 181.0.0.2
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S
Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a
additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*>i 181.0.1.0/24 181.0.0.1 0 100
0 I (ruta publicada por BGP-1)
*>i
181.0.2.0/24 181.0.0.1 0 100 0 i (ruta publicada por BGP-1)
*>i
181.0.3.0/24 181.0.0.1 0 100 0 i (ruta publicada por BGP-1)
*>
181.0.4.0/24 0.0.0.0 0 32768 i
*> 181.0.5.0/24 0.0.0.0 0 32768 i
*> 181.0.6.0/24 0.0.0.0 0 32768 i
*> 181.0.7.0/24 0.0.0.0
0 32768 i
*> 181.0.8.0/24 0.0.0.0 0 32768 i
*> 181.0.9.0/24 0.0.0.0 0 32768 i
* i 200.0.1.0 190.0.0.2 0 100
0 65530 i (ruta publicada por BGP-2)
* i 200.0.2.0 190.0.0.2 0 100
0 65530 I (ruta
publicada por BGP-2)
* i 200.0.3.0 190.0.0.2 0 100
0 65530 I (ruta
publicada por BGP-2)
BGP-3#
BGP-3#sh ip route 200.0.1.0
% Network not in table
BGP-3#
Si el router “no sabe” cómo llegar al siguiente salto
de una ruta, la búsqueda recursiva fallará y la ruta BGP no se podrá agregar a
la tabla.
BGP-3 recibe las rutas con un atributo NEXT_HOP
de 190.0.0.2, pero como no tiene una entrada en su tabla de enrutamiento para
una
subred que incluya 190.0.0.2, la ruta BGP no se
podrá agregar a la tabla.
Si hipotéticamente las rutas se instalaran en la
tabla de enrutamiento sucedería lo siguiente:
6.- Esto se solucionaría de
dos maneras:
6.1.- Implementando
una ruta estática, BGP (tanto iBGP o eBGP), o vía IGP (EIGRP, OSPF, etc…) pero
no es el caso en este lab.
6.2.- Implementando
el atributo next-hop-self en el router BGP-1 para reemplazar el next-hop
190.0.0.2 por la dirección IP
alcanzable por el peer (que esté en su tabla de
enrutamiento), en este caso 181.0.0.1 que es alcanzable ya que es el peer BGP.
7.- Solución:
Si no se va a declarar la red 190.0.0.0/24 en el
BGP, o con algún IGP o ruta estática, se deberá especificar el atributo
NEXT_HOP en el peer BGP.
7.1.- Configuramos el
atributo NEXT-HOP:
BGP-1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
BGP-1(config)#router bgp
65531
BGP-1(config-router)#neighbor
181.0.0.2 next-hop-self
BGP-1(config-router)#end
BGP-1#
7.2.- Verificamos:
7.2.1.- En la tabla BGP de
BGP-3:
BGP-3#sh ip bgp
BGP table version is 31, local router ID is 181.0.0.2
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S
Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a
additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*>i 181.0.1.0/24 181.0.0.1 0 100
0 i
*>i 181.0.2.0/24 181.0.0.1 0 100
0 i
*>i 181.0.3.0/24 181.0.0.1 0 100
0 i
*> 181.0.4.0/24 0.0.0.0 0 32768 i
*> 181.0.5.0/24 0.0.0.0 0 32768 i
*> 181.0.6.0/24 0.0.0.0 0 32768 i
*> 181.0.7.0/24 0.0.0.0 0 32768 i
*> 181.0.8.0/24 0.0.0.0 0 32768 i
*> 181.0.9.0/24 0.0.0.0 0 32768 i
*>i 200.0.1.0
181.0.0.1 0 100
0 65530 I (ahora el
next-hop es el segmento de backbone entre BGP-1 y BGP-3)
*>i 200.0.2.0 181.0.0.1 0 100
0 65530 i
*>i 200.0.3.0 181.0.0.1 0 100
0 65530 i
BGP-3#
7.2.1.- En la tabla de enrutamiento
de BGP-3:
BGP-3#sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP
external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type
1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1,
E2 - OSPF external type 2
i - IS-IS, su - IS-IS
summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * -
candidate default, U - per-user static route
o - ODR, P - periodic
downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % -
next hop override
Gateway of last resort is not set
181.0.0.0/16 is variably
subnetted, 17 subnets, 2 masks
C 181.0.0.0/24 is directly
connected, Vlan1810
L
181.0.0.2/32 is directly connected, Vlan1810
B 181.0.1.0/24 [200/0] via 181.0.0.1,
00:04:08 (ruta publicada por
BGP-1)
B 181.0.2.0/24 [200/0] via 181.0.0.1,
00:04:08 (ruta publicada por
BGP-1)
B 181.0.3.0/24 [200/0] via 181.0.0.1,
00:04:08 (ruta publicada por
BGP-1)
C 181.0.4.0/24 is directly
connected, Vlan1814
L 181.0.4.1/32 is directly
connected, Vlan1814
C 181.0.5.0/24 is directly
connected, Vlan1815
L 181.0.5.1/32 is directly
connected, Vlan1815
C 181.0.6.0/24 is directly
connected, Vlan1816
L 181.0.6.1/32 is directly
connected, Vlan1816
C 181.0.7.0/24 is directly
connected, Vlan1817
L 181.0.7.1/32 is directly
connected, Vlan1817
C 181.0.8.0/24 is directly
connected, Vlan1818
L 181.0.8.1/32 is directly
connected, Vlan1818
C 181.0.9.0/24 is directly
connected, Vlan1819
L 181.0.9.1/32 is directly
connected, Vlan1819
B 200.0.1.0/24 [200/0] via 181.0.0.1,
00:00:46 (ruta ruta
publicada por BGP-2 pero aprendida desde BGP-1)
B 200.0.2.0/24 [200/0] via 181.0.0.1,
00:00:46 (ruta ruta
publicada por BGP-2 pero aprendida desde BGP-1)
B 200.0.3.0/24 [200/0] via 181.0.0.1,
00:00:46 (ruta ruta
publicada por BGP-2 pero aprendida desde BGP-1)
BGP-3#
8.- Análisis del atributo
NEXT-HOP en los anuncios BGP:
8.1.- Anuncio eBGP (external
BGP o entre diferentes AS):
Breve descripción del asunto (obtenido del RFC 4271 que
define el BGP):
The NEXT_HOP is a well-known
mandatory attribute that defines the IP address of the router that SHOULD be
used as the next hop to the
destinations listed in the
UPDATE message. The NEXT_HOP attribute
is calculated as follows:
2) When sending a message to
an external peer, X, and the peer is one IP hop away from the
speaker:
- If the route being
announced was learned from an internal peer or is locally originated, the BGP
speaker can use an
interface address of the
internal peer router (or the internal router) through which the announced
network is reachable
for the speaker for the
NEXT_HOP attribute, provided that
peer X shares a common subnet with this address.
This is a form of
"third party" NEXT_HOP attribute. (o sea BGP-2 y BGP-3 deberían compartir la misma red/subred)(no aplica)
- Otherwise, if the route being announced was
learned from an external peer, the speaker can use an IP address of any
adjacent router (known
from the received NEXT_HOP attribute) that the speaker itself uses for local
route calculation in
the NEXT_HOP attribute,
provided that peer X shares a common subnet with this address. This is a second form of "third
party" NEXT_HOP
attribute. (no aplica)
- Otherwise, if the
external peer to which the route is being advertised shares a common subnet with one of the interfaces
of the announcing BGP speaker, the speaker MAY use the IP address associated with such an
interface in the NEXT_HOP
attribute. This is known as a "first party"
NEXT_HOP attribute. (sí aplica)
- By default (if none of the above conditions apply), the BGP speaker SHOULD use the IP address of the interface that the
speaker uses to establish the BGP connection to peer X in the NEXT_HOP attribute. (también aplica)
Este es el anuncio (UPDATE) entre BGP-1 y BGP-2
para las redes que publica BGP-3, se puede ver que el next-hop no es el
del router BGP-3 sino que es el mismo BGP-1 que
se declara next-hop:
Frame 1: 99 bytes on wire (792 bits), 99 bytes captured (792 bits)
Ethernet II, Src: 00:17:95:c0:ac:a2, Dst: d4:ca:6d:a4:2e:22
Internet Protocol Version 4, Src: 190.0.0.1, Dst: 190.0.0.2
Transmission Control Protocol, Src Port: 15525, Dst Port: 179, Seq: 1,
Ack: 1, Len: 45
Border Gateway Protocol - UPDATE Message
Marker:
ffffffffffffffffffffffffffffffff
Length: 45
Type: UPDATE Message (2)
Withdrawn Routes Length: 0
Total Path Attribute Length: 18
Path attributes
Path Attribute - ORIGIN:
IGP
Path Attribute - AS_PATH:
65531
Path Attribute - NEXT_HOP: 190.0.0.1
Network Layer Reachability
Information (NLRI)
181.0.4.0/24
181.0.5.0/24
181.0.6.0/24
8.2.- Anuncios iBGP
(internal BGP o dentro del mismo AS):
Breve descripción del asunto (obtenido del RFC 4271 que
define el BGP):
The NEXT_HOP is a well-known
mandatory attribute that defines the IP address of the router that SHOULD be
used as the next hop to the
destinations listed in the
UPDATE message. The NEXT_HOP attribute
is calculated as follows:
1) When sending a message to an internal
peer, if the route is not locally originated, the BGP speaker SHOULD NOT modify the
NEXT_HOP attribute unless it has been
explicitly configured to announce its own IP address as the
NEXT_HOP.
When announcing a locally-originated
route to an internal peer, the BGP speaker SHOULD use the interface address of
the router
through which the announced network is
reachable for the speaker as the NEXT_HOP.
If the route is directly connected to
the speaker, or if the interface address of the router through which the
announced network is
reachable for the speaker is the
internal peer's address, then the BGP speaker SHOULD use its own IP address for
the NEXT_HOP
attribute (the address of the
interface that is used to reach the peer).
8.2.1.- Captura del update
sin next-hop-self declarado:
Frame 1: 113 bytes on wire (904 bits), 113 bytes captured (904 bits)
Ethernet II, Src: 00:17:95:c0:ac:a3, Dst: cc:46:d6:2b:5a:54
Internet Protocol Version 4, Src: 181.0.0.1, Dst: 181.0.0.2
Transmission Control Protocol, Src Port: 179, Dst Port: 31055, Seq: 1,
Ack: 1, Len: 59
Border Gateway Protocol - UPDATE Message
Marker:
ffffffffffffffffffffffffffffffff
Length: 59
Type: UPDATE Message (2)
Withdrawn Routes Length: 0
Total Path Attribute Length: 32
Path attributes
Path Attribute - ORIGIN:
IGP
Path Attribute - AS_PATH: 65530
Path Attribute - NEXT_HOP: 190.0.0.2
Path Attribute -
MULTI_EXIT_DISC: 0
Path Attribute -
LOCAL_PREF: 100
Network Layer Reachability
Information (NLRI)
200.0.3.0/24
En el caso de que la red 190.0.0.0/24 estuviese
publicada o alcanzable:
En el caso de que la red 190.0.0.0/24 no estuviese publicada o fuese inalcanzable:
8.2.2.- Captura del update
con next-hop-self:
Frame 1: 113 bytes on wire (904 bits), 113 bytes captured (904 bits)
Ethernet II, Src: 00:17:95:c0:ac:a3, Dst: cc:46:d6:2b:5a:54
Internet Protocol Version 4, Src: 181.0.0.1, Dst: 181.0.0.2
Transmission Control Protocol, Src Port: 179, Dst Port: 31055, Seq: 236,
Ack: 39, Len: 59
Border Gateway Protocol - UPDATE Message
Marker:
ffffffffffffffffffffffffffffffff
Length: 59
Type: UPDATE Message (2)
Withdrawn Routes Length: 0
Total Path Attribute Length: 32
Path attributes
Path Attribute - ORIGIN:
IGP
Path Attribute - AS_PATH:
65530
Path Attribute - NEXT_HOP: 181.0.0.1
Path Attribute -
MULTI_EXIT_DISC: 0
Path Attribute - LOCAL_PREF:
100
Network Layer Reachability
Information (NLRI)
200.0.3.0/24
Recordemos que en este escenario la red/subred
190.0.0.0/24 no está publicada en el BGP, y por lo tanto utilizaremos 181.0.0.1
como next-hop.
BGP-1#sh runn | sec bgp (no esta declarada la red/subred 190.0.0.0/24)
router bgp 65531
no synchronization
bgp log-neighbor-changes
network 181.0.1.0 mask
255.255.255.0
network 181.0.2.0 mask
255.255.255.0
network 181.0.3.0 mask
255.255.255.0
neighbor 181.0.0.2 remote-as 65531
neighbor 181.0.0.2 next-hop-self
neighbor 190.0.0.2 remote-as 65530
no auto-summary
BGP-1#
(2023) Who need
information ?
Rosario, Argentina