Scott,
I think the problem is with you putting 'no synchronization' in
router1. I would also say that if you did a ping to 33.33.33.1 from
router2 it would work because the 192 net is reachable from router2. When
you issue a 'no synchronization' you are saying that if this route is
being announced to me via an IBGP peer, I will install it into the
routing
table regardless. Keep in mind it will go into the routing
table without any
knowledge of whether the next-hop address is reachable. You would need an
IGP or static routes to ensure that all next-hop
addresses are reachable from all IBGP peers. It's your responsibility to
verify that a next-hop route exists for every bgp route.
> This is my confusion: I was under the impression that routes do not
> get installed into routing tables if there is no route for the next-hop
> address. Specifically, since R1 does not know how to get to
> 192.1.1.1, the 33.33.33.0 route should not get installed.
You have described the normal behavior, but you have also overridden this
behavior with 'no synchronization'.
hope this helps,
On Tue, 20 Feb 2001, scott wrote:
> Hello all - I may have been working on this too long. Take a look
> at the following network.
>
> AS100 iBGP AS100
> 22.22.22.0 11.11.11.0
> R2-173.4.175.19------173.4.175.17-R1 <synchronization turned
>
>
> 192.1.1.2
> off on R1 and R2
> |
> |
> | eBGP
> |
> |
> |
> 192.1.1.1
> R3
> AS300
> |
> 33.33.33.0
>
> Router3
> router bgp 300
> network 33.33.33.0 mask 255.255.255.0
> neighbor 192.1.1.2 remote-as 100
>
> Router2
> router bgp 100
> no synchronization
> network 22.22.22.0 mask 255.255.255.0
> neighbor 173.4.175.17 remote-as 100
> neighbor 192.1.1.1 remote-as 300
>
> Router1
> router bgp 100
> no synchronization
> network 11.11.11.0 mask 255.255.255.0
> neighbor 173.4.175.19 remote-as 100
>
>
> If I do a show ip route on R1 I will get the following information
> on the 33.33.33.0 network.
> B 33.33.33.0 [200/0] via 192.1.1.1
>
> If I do a ping to 33.33.33.1 (loopback on R3), the ping will fail and
> that is
> expected. The 192 network is not advertised so R1 does not have a
> route to it.
>
> This is my confusion: I was under the impression that routes do not
> get installed into routing tables if there is no route for the next-hop
> address. Specifically, since R1 does not know how to get to
> 192.1.1.1, the 33.33.33.0 route should not get installed.
>
> Also take a look at the Cisco Press BSCN study guide -pp 347
> to 348. It too seems to indicate that the route, in its example,
> should not get installed.
>
> **So why am I seeing the 33.33.33.0 route if I don't have a route
> to 192.1.1.1?**
>
> What am I missing here?
>
> Thank you!
>
> Scott Chapin
>
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