(Até a parte fácil é difícil)
Existem três formas de adicionar uma rota default na tabela BGP.
Vamos usar a topologia e as configurações abaixo, como ponto de partida, e mostrar estas opções.
R1:
interface Ethernet0/0
ip address 10.1.1.1 255.255.255.0
!
interface Ethernet0/1
ip address 10.10.0.1 255.255.255.0
!
interface Ethernet0/2
ip address 172.16.0.1 255.255.255.0
!
router bgp 10
redistribute connected
redistribute static
neighbor 10.1.1.2 remote-as 10
neighbor 10.1.1.2 next-hop-self
neighbor 10.10.0.2 remote-as 30
!
ip route 0.0.0.0 0.0.0.0 172.16.0.2
ip route 4.4.4.4 255.255.255.255 172.16.0.2R2:
interface Ethernet0/0
ip address 10.1.1.2 255.255.255.0
!router bgp 10
redistribute connected
neighbor 10.1.1.1 remote-as 10R3:
interface Ethernet0/1
ip address 10.10.0.2 255.255.255.0
!
router bgp 30
redistribute connected
neighbor 10.10.0.1 remote-as 10R4:
interface Loopback4
ip address 4.4.4.4 255.255.255.255
!
interface Loopback200
ip address 200.1.1.1 255.255.255.255
!
interface Ethernet0/2
ip address 172.16.0.2 255.255.255.0
!
ip route 10.1.1.0 255.255.255.0 172.16.0.1
ip route 10.10.0.0 255.255.255.0 172.16.0.1
Redistribute + Default-Information
Podemos inserir uma rota default no BGP usando os comandos redistribute e default-information originate.
Observe que no roteador R1 temos uma rota default (estática) e também o comando redistribute static já configurado (redistribuindo a outra rota estática). No entanto a rota default não está na tabela BGP dos roteadores R1, R2 e R3.
R1#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 172.16.0.2 to network 0.0.0.0
S* 0.0.0.0/0 [1/0] via 172.16.0.2
4.0.0.0/32 is subnetted, 1 subnets
S 4.4.4.4 [1/0] via 172.16.0.2
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Ethernet0/0
L 10.1.1.1/32 is directly connected, Ethernet0/0
C 10.10.0.0/24 is directly connected, Ethernet0/1
L 10.10.0.1/32 is directly connected, Ethernet0/1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.0.0/24 is directly connected, Ethernet0/2
L 172.16.0.1/32 is directly connected, Ethernet0/2
R1#
R1#sh ip bgp
BGP table version is 11, local router ID is 172.16.0.1
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
*> 4.4.4.4/32 172.16.0.2 0 32768 ?
*> 10.1.1.0/24 0.0.0.0 0 32768 ?
* i 10.1.1.2 0 100 0 ?
*> 10.10.0.0/24 0.0.0.0 0 32768 ?
* 10.10.0.2 0 0 30 ?
*> 172.16.0.0/24 0.0.0.0 0 32768 ?
R1#
R2#sho ip bgp
BGP table version is 20, local router ID is 10.1.1.2
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 4.4.4.4/32 10.1.1.1 0 100 0 ?
* i 10.1.1.0/24 10.1.1.1 0 100 0 ?
*> 0.0.0.0 0 32768 ?
*>i 10.10.0.0/24 10.1.1.1 0 100 0 ?
*>i 172.16.0.0/24 10.1.1.1 0 100 0 ?
R2#
R3#sh ip bgp
BGP table version is 16, local router ID is 10.10.0.2
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
*> 4.4.4.4/32 10.10.0.1 0 0 10 ?
*> 10.1.1.0/24 10.10.0.1 0 0 10 ?
* 10.10.0.0/24 10.10.0.1 0 0 10 ?
*> 0.0.0.0 0 32768 ?
*> 172.16.0.0/24 10.10.0.1 0 0 10 ?
R3#
Vamos agora inserir o comando default-information originate para que a rota default também seja redistribuída (sem esse comando o BGP redistribui as rotas estáticas, mas não a rota default).
R1#conf t
R1(config)#router bgp 10
R1(config-router)# default-information originate
R1(config-router)#end
R1#
R1#sh ip bgp
BGP table version is 12, local router ID is 172.16.0.1
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
*> 0.0.0.0 172.16.0.2 0 32768 ?
*> 4.4.4.4/32 172.16.0.2 0 32768 ?
*> 10.1.1.0/24 0.0.0.0 0 32768 ?
* i 10.1.1.2 0 100 0 ?
*> 10.10.0.0/24 0.0.0.0 0 32768 ?
* 10.10.0.2 0 0 30 ?
*> 172.16.0.0/24 0.0.0.0 0 32768 ?
R1#
R2#sh ip bgp
BGP table version is 21, local router ID is 10.1.1.2
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 0.0.0.0 10.1.1.1 0 100 0 ?
*>i 4.4.4.4/32 10.1.1.1 0 100 0 ?
* i 10.1.1.0/24 10.1.1.1 0 100 0 ?
*> 0.0.0.0 0 32768 ?
*>i 10.10.0.0/24 10.1.1.1 0 100 0 ?
*>i 172.16.0.0/24 10.1.1.1 0 100 0 ?
R2#
R3#sh ip bgp
BGP table version is 17, local router ID is 10.10.0.2
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
*> 0.0.0.0 10.10.0.1 0 0 10 ?
*> 4.4.4.4/32 10.10.0.1 0 0 10 ?
*> 10.1.1.0/24 10.10.0.1 0 0 10 ?
* 10.10.0.0/24 10.10.0.1 0 0 10 ?
*> 0.0.0.0 0 32768 ?
*> 172.16.0.0/24 10.10.0.1 0 0 10 ?
R3#
Também podemos redistribuir uma rota default aprendida via protocolo de roteamento, usando o mesmo conceito (redistribute + default-information).
Vamos remover a rota default do R1 e configurar OSPF entre ele e o R4 (que divulgará a rota default).
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#no ip route 0.0.0.0 0.0.0.0 172.16.0.2
R1(config)#interface Ethernet0/2
R1(config-if)# ip ospf 40 area 0
R1(config-if)#
R4#conf t
R4(config)#interface Ethernet0/2
R4(config-if)# ip ospf 40 area 0
R4(config-if)#exit
R4(config)#router ospf 40
R4(config-router)# default-information originate always
R1#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 172.16.0.2 to network 0.0.0.0
O*E2 0.0.0.0/0 [110/1] via 172.16.0.2, 00:00:15, Ethernet0/2
4.0.0.0/32 is subnetted, 1 subnets
S 4.4.4.4 [1/0] via 172.16.0.2
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Ethernet0/0
L 10.1.1.1/32 is directly connected, Ethernet0/0
C 10.10.0.0/24 is directly connected, Ethernet0/1
L 10.10.0.1/32 is directly connected, Ethernet0/1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.0.0/24 is directly connected, Ethernet0/2
L 172.16.0.1/32 is directly connected, Ethernet0/2
R1#
Agora que R1 tem um rota default em sua tabela de roteamento (aprendida via OSPF), basta redistribuir o OSPF no BGP.
R1#conf t
R1(config)#router bgp 10
R1(config-router)#redistribute ospf 40 match external
R1(config-router)#end
R1#sh ip bgp
BGP table version is 14, local router ID is 172.16.0.1
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
*> 0.0.0.0 172.16.0.2 1 32768 ?
*> 4.4.4.4/32 172.16.0.2 0 32768 ?
*> 10.1.1.0/24 0.0.0.0 0 32768 ?
* i 10.1.1.2 0 100 0 ?
*> 10.10.0.0/24 0.0.0.0 0 32768 ?
* 10.10.0.2 0 0 30 ?
*> 172.16.0.0/24 0.0.0.0 0 32768 ?
R1#
R2# sh ip bgp
BGP table version is 23, local router ID is 10.1.1.2
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 0.0.0.0 10.1.1.1 1 100 0 ?
*>i 4.4.4.4/32 10.1.1.1 0 100 0 ?
* i 10.1.1.0/24 10.1.1.1 0 100 0 ?
*> 0.0.0.0 0 32768 ?
*>i 10.10.0.0/24 10.1.1.1 0 100 0 ?
*>i 172.16.0.0/24 10.1.1.1 0 100 0 ?
R2#
R3#sh ip bgp
BGP table version is 19, local router ID is 10.10.0.2
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
*> 0.0.0.0 10.10.0.1 1 0 10 ?
*> 4.4.4.4/32 10.10.0.1 0 0 10 ?
*> 10.1.1.0/24 10.10.0.1 0 0 10 ?
* 10.10.0.0/24 10.10.0.1 0 0 10 ?
*> 0.0.0.0 0 32768 ?
*> 172.16.0.0/24 10.10.0.1 0 0 10 ?
R3#
Usando o comando network
Outra opção para divulgar uma rota default via BGP, é usando o comando network.
Utilizando nosso exemplo, vamos remover a redistribuição do OSPF e colocar o comando network 0.0.0.0.
Importante notar que para que a divulgação funcione é preciso que R1 tenha uma rota default em sua tabela de roteamento (e temos, aprendida via OSPF).
R1#conf t
R1(config)#router bgp 10
R1(config-router)#no redistribute ospf 40 match external
R1(config-router)#network 0.0.0.0
R1(config-router)#end
R1#
R1#sh ip bgp
BGP table version is 16, local router ID is 172.16.0.1
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
*> 0.0.0.0 172.16.0.2 1 32768 i
*> 4.4.4.4/32 172.16.0.2 0 32768 ?
*> 10.1.1.0/24 0.0.0.0 0 32768 ?
* i 10.1.1.2 0 100 0 ?
*> 10.10.0.0/24 0.0.0.0 0 32768 ?
* 10.10.0.2 0 0 30 ?
*> 172.16.0.0/24 0.0.0.0 0 32768 ?
R1#
R2#sh ip bgp
BGP table version is 25, local router ID is 10.1.1.2
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 0.0.0.0 10.1.1.1 1 100 0 i
*>i 4.4.4.4/32 10.1.1.1 0 100 0 ?
* i 10.1.1.0/24 10.1.1.1 0 100 0 ?
*> 0.0.0.0 0 32768 ?
*>i 10.10.0.0/24 10.1.1.1 0 100 0 ?
*>i 172.16.0.0/24 10.1.1.1 0 100 0 ?
R2#
R3#sh ip bgp
BGP table version is 21, local router ID is 10.10.0.2
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
*> 0.0.0.0 10.10.0.1 1 0 10 i
*> 4.4.4.4/32 10.10.0.1 0 0 10 ?
*> 10.1.1.0/24 10.10.0.1 0 0 10 ?
* 10.10.0.0/24 10.10.0.1 0 0 10 ?
*> 0.0.0.0 0 32768 ?
*> 172.16.0.0/24 10.10.0.1 0 0 10 ?
R3#
Neighbor default-originate
Por fim, podemos anunciar uma rota default via BGP usando o comando neighbor x.x.x.x default-originate.
Neste caso o roteador anuncia a rota default para o neighbor especificado, mas não insere a rota default na tabela de roteamento local.
Quando usamos este comando o roteador faz o anuncio da rota default sem verificar se ele tem uma rota default em sua tabela de roteamento, mas essa verificação pode ser configurada usando route-map.
R1#conf t
R1(config)#int et0/2
R1(config-if)#no ip ospf 40 area 0
R1(config-if)#exit
R1(config)#router bgp 10
R1(config-router)#no network 0.0.0.0
R1(config-router)#no default-information originate
R1(config-router)#neighbor 10.1.1.2 default-originate
R1(config-router)#end
R1#
R1#sh ip bgp
BGP table version is 18, local router ID is 172.16.0.1
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 0.0.0.0 0.0.0.0 0 i
*> 4.4.4.4/32 172.16.0.2 0 32768 ?
*> 10.1.1.0/24 0.0.0.0 0 32768 ?
* i 10.1.1.2 0 100 0 ?
*> 10.10.0.0/24 0.0.0.0 0 32768 ?
* 10.10.0.2 0 0 30 ?
*> 172.16.0.0/24 0.0.0.0 0 32768 ?
R1#sh ip route 0.0.0.0
% Network not in table
R1#
R2#sh ip bgp
BGP table version is 27, local router ID is 10.1.1.2
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 0.0.0.0 10.1.1.1 0 100 0 i
*>i 4.4.4.4/32 10.1.1.1 0 100 0 ?
* i 10.1.1.0/24 10.1.1.1 0 100 0 ?
*> 0.0.0.0 0 32768 ?
*>i 10.10.0.0/24 10.1.1.1 0 100 0 ?
*>i 172.16.0.0/24 10.1.1.1 0 100 0 ?
R2#
R3#sh ip bgp
BGP table version is 22, local router ID is 10.10.0.2
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
*> 4.4.4.4/32 10.10.0.1 0 0 10 ?
*> 10.1.1.0/24 10.10.0.1 0 0 10 ?
* 10.10.0.0/24 10.10.0.1 0 0 10 ?
*> 0.0.0.0 0 32768 ?
*> 172.16.0.0/24 10.10.0.1 0 0 10 ?
R3#
OBS: Em alguns documentos fala que quando usamos o comando neighbor x.x.x.x default-originate o roteador não insere a rota default na tabela BGP local. O que vi (usando o UNL) é que a rota é sim inserida na tabela BGP, mas ela não é a best route. Acredito que essa mudança no comportamento se deve a versão do IOS (ou talvez por conta do simulador).
Até a próxima.
(Postado originalmente em: http://brainwork.com.br/2016/11/04/rota-default-no-bgp/)
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