BGP Help

rakem

Hey guys... im just getting into BGP for the first time... i have set up the following lab in dynamips:



Im having issues with getting connectivity between the two AS'. Here is the config from routers 2, 3 and 4

R2
interface Serial1/0
ip address 192.168.1.2 255.255.255.252
serial restart-delay 0
!
interface Serial1/1
ip address 100.1.1.1 255.255.255.252
serial restart-delay 0
!
router ospf 10
log-adjacency-changes
network 100.1.1.0 0.0.0.3 area 0
network 192.168.1.0 0.0.0.3 area 0
!
router bgp 65100
no synchronization
bgp log-neighbor-changes
neighbor 100.1.1.2 remote-as 65300
no auto-summary

---

R3
interface Serial1/0
ip address 100.1.1.2 255.255.255.252
serial restart-delay 0
!
interface Serial1/1
ip address 200.1.1.1 255.255.255.252
serial restart-delay 0
!
router bgp 65300
no synchronization
bgp log-neighbor-changes
neighbor 100.1.1.1 remote-as 65100
neighbor 200.1.1.2 remote-as 65200
no auto-summary

---

R4
interface Serial1/0
ip address 200.1.1.2 255.255.255.252
serial restart-delay 0
!
interface Serial1/1
ip address 192.168.20.1 255.255.255.252
serial restart-delay 0

router ospf 20
log-adjacency-changes
network 192.168.20.0 0.0.0.3 area 0
network 200.1.1.0 0.0.0.3 area 0
!
router bgp 65200
no synchronization
bgp log-neighbor-changes
neighbor 200.1.1.1 remote-as 65300
no auto-summary


the routing table on R3 only has its directly connected routes... im obviously missing something here, as mentioned this is the first time i have looked at BGP.... any pointers from you learned people would be great!

until then i will do some research.

mikej412

You don't have any BGP network statements, so BGP has nothing to advertise.

georgemc

How about BGP network statements to tell BGP what to advertise?

George

EDIT: lol, Mike beat me to it...

rakem

right... that would make sense. hahah.. So im guessing its like other routing protocols where you just advertise your directly connected networks?

EdTheLad

rakem wrote:

right... that would make sense. hahah.. So im guessing its like other routing protocols where you just advertise your directly connected networks?

You guess wrong, you advertise either directly connected networks or networks learned via the igp,the main thing to watch is that the next-hop address of the address learned via an igp is reachable,otherwise bgp wont advertise it.

mikej412

Nope. Other routing protocols use the network statement to determine the interfaces that participate in the routing process.

In BGP the network statement defines the networks that will be advertised. You can also redistribute into BGP or summarize to get BGP to advertise routes.

Keep reading.... BGP is lots of fun!

georgemc wrote:

EDIT: lol, Mike beat me to it...

Well I know how you feel, Ed beat me to the "valid next hop" .... just because you tell BGP to advertise something doesn't mean it will listen to you At least synchronization is now disabled by default on the more recent IOS versions.... which makes it even easier to mess things up with BGP if you're not careful.

rakem

right thanks for that guys... so i did some more reading and the cisco press self study books says:

"This command (the network command) does not identify the interfaces on which to run BGP; it states the networks that are available within the AS"

So here is my new configs: i also had to do a bunch of redistribution to get the routing tables on 1 and 5 to have full connectivity. Let me know what you guys think:

(note R1 has network 11.0.0.0 connected and R5 has 15.0.0.0)

R2
router ospf 10
log-adjacency-changes
redistribute bgp 65100 metric 600 subnets
network 100.1.1.0 0.0.0.3 area 0
network 192.168.1.0 0.0.0.3 area 0
!
router bgp 65100
synchronization
bgp log-neighbor-changes
network 11.1.0.0 mask 255.255.0.0
network 100.1.1.0 mask 255.255.255.252
network 192.168.1.0 mask 255.255.255.252
redistribute ospf 10 metric 300
neighbor 100.1.1.2 remote-as 65300
no auto-summary

---

R3
router bgp 65300
synchronization
bgp log-neighbor-changes
network 100.1.1.0 mask 255.255.255.252
network 200.1.1.0 mask 255.255.255.252
neighbor 100.1.1.1 remote-as 65100
neighbor 200.1.1.2 remote-as 65200
no auto-summary

---

R4
router ospf 20
log-adjacency-changes
redistribute bgp 65200 metric 600 subnets
network 192.168.20.0 0.0.0.3 area 0
network 200.1.1.0 0.0.0.3 area 0
!
router bgp 65200
synchronization
bgp log-neighbor-changes
network 15.1.0.0 mask 255.255.0.0
network 192.168.20.0 mask 255.255.255.252
network 200.1.1.0 mask 255.255.255.252
redistribute ospf 20 metric 300
neighbor 200.1.1.1 remote-as 65300
no auto-summary
!

As a result of this config R1 has this routing table:
Gateway of last resort is not set

100.0.0.0/30 is subnetted, 1 subnets
O 100.1.1.0 [110/128] via 192.168.1.2, 00:40:23, Serial1/0
200.1.1.0/30 is subnetted, 1 subnets
O E2 200.1.1.0 [110/600] via 192.168.1.2, 00:40:23, Serial1/0
192.168.20.0/30 is subnetted, 1 subnets
O E2 192.168.20.0 [110/600] via 192.168.1.2, 00:40:23, Serial1/0
11.0.0.0/24 is subnetted, 2 subnets
C 11.1.2.0 is directly connected, Loopback2
C 11.1.1.0 is directly connected, Loopback1
192.168.1.0/30 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, Serial1/0
15.0.0.0/32 is subnetted, 2 subnets
O E2 15.1.2.1 [110/600] via 192.168.1.2, 00:14:18, Serial1/0
O E2 15.1.1.1 [110/600] via 192.168.1.2, 00:14:27, Serial1/0
R1#

R5 has this:
Gateway of last resort is not set

100.0.0.0/30 is subnetted, 1 subnets
O E2 100.1.1.0 [110/600] via 192.168.20.1, 00:21:21, Serial1/0
200.1.1.0/30 is subnetted, 1 subnets
O 200.1.1.0 [110/128] via 192.168.20.1, 00:21:21, Serial1/0
192.168.20.0/30 is subnetted, 1 subnets
C 192.168.20.0 is directly connected, Serial1/0
11.0.0.0/32 is subnetted, 2 subnets
O E2 11.1.2.1 [110/600] via 192.168.20.1, 00:01:28, Serial1/0
O E2 11.1.1.1 [110/600] via 192.168.20.1, 00:01:28, Serial1/0
192.168.1.0/30 is subnetted, 1 subnets
O E2 192.168.1.0 [110/600] via 192.168.20.1, 00:21:21, Serial1/0
15.0.0.0/24 is subnetted, 2 subnets
C 15.1.2.0 is directly connected, Loopback2
C 15.1.1.0 is directly connected, Loopback1
R5#

so they have full connectivity between them... I could have done this with static routes too a suppose. So does this look ok? have I used the network command correctly in BGP?

cheers.

mikej412

Save the redistribution for later..... a lot later.

With Synchronization enabled, the networks in the BGP network statement must also be learned by an IGP before they will be advertised.... but the first check BGP does is the "next-hop reachable check."

Keep reading and try to keep your labs as simple as possible to start

rakem

mikej412 wrote:

Save the redistribution for later..... a lot later.

With Synchronization enabled, the networks in the BGP network statement must also be learned by an IGP before they will be advertised..

so in AS65300 where there is no IGP running what would be the best way to set that up?

and should i be able to this this network design working correctly without redistribution? I only needed it to get the 11.0.0.0 to show up int R5 routing table and for 15.0.0.0 to show up in R1 table..

I suppose a default route on the end routers would be better than redistribution.

EdTheLad

If you dont have an IGP running in AS65300 you dont have any routes to advertise into bgp so you dont need to do anything.Redistribution is a big no no in bgp, 99% of the time you wont even consider using it.
In your config under bgp you have "network 15.1.0.0 mask 255.255.0.0" and " network 11.1.0.0 mask 255.255.0.0" . If you do a "sh ip route" do you have routes 15.1.0.0/16 and 11.1.0.0/16, if you dont have an exact match bgp will not advertise the routes,you must be careful on mask length.
From your questions its apparent that you are configuring bgp without understanding how it works, i suggest you do as mike suggested earlier and start reading multiple sources and have a goal of what you want to accomplish when it comes to labbing it up.