Injecting IGP routes into BGP

Posted in NETWORKING/IP ROUTING by edeguzman on October 3, 2007

This is a configuration wherein routes in the routing table is place in the BGP table.
The routes in the BGP table will be advertised to its BGP peer whether its inter-AS or
intra-AS. Below is the configuration.

router eigrp 200
passive-interface s0
network 192.168.1.0
network 192.168.100.0
!
router bgp 200
redistribute eigrp 200
neighbor 192.168.1.226 remote-as 100
!

The configuration shows that I used the EIGRP as my IGP running within the AS 200,
a passive-interface is configured in its process, wherein it means that in the interface serial 0 it will not advertise neither receives updates and it will not even send a hello packet in that interface.

In the BGP process, a redistribute eigrp 200 is configured this will simply redistribute the routes learned via EIGRP into the BGP table. You can see its results by making a show ip bgp, from there you can see the routes of EIGRP that is distributed into the BGP table. This configuration is not that good because there are drawbacks using this kind of configuration. Because all the routes learned in EIGRP is place in the BGP table in which in some cases this is unacceptable. There are routes in EIGRP that you might not consider to be part of your BGP table. Another reason is the problem of route feedback, when using redistribution the route feedback is always a possibility in your network. Because of this you must apply route policies to compensate the
situation.

Below is another configuration of injecting IGP routes into BGP.

router eigrp 200
passive-interface s0
network 192.168.1.0
network 192.168.100.0
!
router BGP 200
network 192.168.1.216 mask 255.255.255.252
network 192.168.100.0
network 192.168.200.0
neighbor 192.168.1.226 remote-as 100

As you observe in the BGP process, that a network command replaced the
redistribution command. This is better way than redistributing because you
had fully control on the networks that you want to include in your BGP table.

Advertisements

IBGP over IGP

Posted in NETWORKING/IP ROUTING by edeguzman on October 3, 2007

This configuration is one of the router within the AS 100. Basically on the laboratory there are 3 routers present within the AS. Two routers serve as the Border Gateway, each of them runs a BGP process and at the same time an OSPF process runs as its IGP. One of the Border Gateway is connected to a stub AS and the other Border Gateway is connected by two stub AS. The other router within the AS just runs an OSPF connecting the two Border Gateway.

Below is the configuration of one of the border gateway.

interface Loopback0
ip address 192.168.255.254 255.255.255.255
!
interface Ethernet0/0
ip address 192.168.1.221 255.255.255.252
!
interface Ethernet0/1
ip address 192.168.1.193 255.255.255.252
!
interface Serial1/0
ip address 192.168.1.226 255.255.255.252
no fair-queue
clockrate 64000
!
interface Serial1/1
ip address 192.168.1.209 255.255.255.252
clockrate 64000
!
interface Serial1/2
no ip address
shutdown
!
interface Serial1/3
no ip address
shutdown
!
router ospf 100
redistribute bgp 100 subnets
network 192.168.1.193 0.0.0.0 area 0
network 192.168.1.221 0.0.0.0 area 0
network 192.168.255.254 0.0.0.0 area 0
!
router bgp 100
timers bgp 3 9
neighbor 192.168.1.210 remote-as 300
neighbor 192.168.1.210 default-originate
neighbor 192.168.1.225 remote-as 200
neighbor 192.168.255.253 remote-as 100
neighbor 192.168.255.253 update-source Loopback0
neighbor 192.168.255.253 next-hop-self
!
ip classless
no ip http server
!
!
!
line con 0
transport input none
line aux 0
line vty 0 4
password passkey
login
!
end

Neighbor 192.168.255.253 update-source Loopback0 – this command simply causes the BGP messages to be sourced from the IP address of the loopback interface rather than from the physical interface. Without this command, the TCP source of the TCP sessions would be the outgoing interface and not the loopback interface.

timers bgp 3 9 – this command basically change the time of the keepalive message
being send to a peer and the holddown time. 3 is the keepalive message and 9 is the holddown time.

neighbor 192.168.1.210 default-originate – this command simply advertise a default-
route to the neighboring peer.

The other commands are already explained from my previous post. I got heavy day thats why I felt tired. This one is quick post in one of configuration I did for the day.