questin about the output sh ip bgp command...

xine xine · ‎01-16-2010

Hi !

I'm currently doing some lab for my CCNP BSCI certification exam.

I would like to understand why in the output of command "show ip bgp" on router PXR2 I see :

Network Next Hop Metric LocPrf Weight Path

192.168.200.2 0

64999 64997 i

* i 192.168.200.4 0 100 0

64998 64997 i

*> 192.168.200.4 0 64998 64997 i

The path are'nt learned for AS 65001 (why the "i" is there) and the path do not pas throw the AS 64997. The AS 64998 and 64999 are directly neigbor router of the local router AS frame cloud is layer 2 network....

Also some line have only a neigbor address router but no network ! What those lines are meaning ??

In same ouput, some line have an i at the start to the line, what is this meaning ?

Some one can explain thoses behavior ?

in the attached file the output of all router and a visio (in PDF format) of my lab setup. all router running BGP have also an show ip bgp output command in there sh running configuration files.

Thanks a lot in advanced !

Edison Ortiz · ‎01-17-2010

I'm currently doing some lab for my CCNP BSCI certification exam.

I would like to understand why in the output of command "show ip bgp" on router PXR2 I see :

Network    Next Hop            Metric LocPrf Weight Path

                192.168.200.2    0

                               64999 64997 i

* i             192.168.200.4    0        100     0

64998 64997 i

*>             192.168.200.4    0                               64998 64997 i

The path are'nt learned for AS 65001 (why the "i" is there) and the path do not pas throw the AS 64997. The AS 64998 and 64999 are directly neigbor router of the local router AS frame cloud is layer 2 network....

Router PXR2 has 3 BGP peers announcing the same network and one peer is chosen as best route (192.168.200.4).

From those peers, you also learn from your iBGP neighbor (65001) but the AS Path information isn't included on iBGP peer exchange and that's the reason you don't see this information. It seems you aren't modifying the next-hop on the iBGP peering as the next-hop remained unchanged (192.168.200.4).

Regarding your other queries, the answer is the same. You will have an entry from each BGP peer that is announcing the network to you.

One entry will be considered as best route. In the case of the 'i', in the output - it indicates the route was learned from an iBGP peer.

Regards,

Edison.

xine xine · ‎01-17-2010

Hi Edison,

I not sure I'm fully understanding you, (Excuse me my primary language is French) or maybe I had missed explain myself....

In this output.... (I had moved a little bit moved the text over each other because of the limitation of this interface)

Here what was'nt clear te me is why the first column is empty inm the blue oblong, those next hop are use full to reach which network ? But by I wrote the answer to you I had seam the answer to my question, all thoses 4 next hop address are usefull to reach 200.200.200.200 network. But a new question in the same oblong we have twice time the same next hop address with same path but with different value under column metric and local preference, one of them have no value there, could you explain to me why we have twice time the same next hop addre with different value as metric and local preference ?

Why AS

Edison Ortiz · ‎01-17-2010

xine32@gmail.com

Hi !

I'm currently doing some lab for my CCNP BSCI certification exam.

I would like to understand why in the output of command "show ip bgp" on router PXR2 I see :

Network Next Hop Metric LocPrf Weight Path

192.168.200.2 0

64999 64997 i

* i 192.168.200.4 0 100 0

64998 64997 i

*> 192.168.200.4 0 64998 64997 i

The path are'nt learned for AS 65001 (why the "i" is there) and the path do not pas throw the AS 64997. The AS 64998 and 64999 are directly neigbor router of the local router AS frame cloud is layer 2 network....

Router PXR2 has 3 BGP peers announcing the same network and one peer is chosen as best route (192.168.200.4).

From those peers, you also learn from your iBGP neighbor (65001) but the AS Path information isn't included on iBGP peer exchange and that's the reason you don't see this information. It seems you aren't modifying the next-hop on the iBGP peering as the next-hop remained unchanged (192.168.200.4).

Regarding your other queries, the answer is the same. You will have an entry from each BGP peer that is announcing the network to you.

One entry will be considered as best route. In the case of the 'i', in the output - it indicates the route was learned from an iBGP peer.

Regards,

Edison.

xine xine · ‎01-18-2010

Hi Edison,

On previous post you had answered me an "i" at the start of the line is meaning this path or network was learnedfrom an iBGP.

When path is learn from iBGP AS path information is not available.

I refer back to my last post with blue oblong, the network 200.200.200.200/32 was learned from an iBGP and used path throught 192.168.200.4 learned from iBGP or an eBGP ?

because AS path is always available I think is by an eBGP same as all other path to this network. Also I had remark I have only a local preference value when the entry as start with an "i". We have always an metric value except for the last two entry (in the order of the output), where one of then was duplicated with metric and local preference value And I still do not understand thoses differences between them...

Thanks a lot in advance !

xine xine · ‎01-19-2010

Hi !

I had add the command neighbor next-hop-self command on all of my BGP router in my configuration. Also, I had removed network command for network 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24 from bgp configuration. The 10 network are a part of network where BGP is not running, but only EIGRP is running (see in the attached file in the first post)

The new routing table I have now makes sense to me, but definitely thoses previously posted do not.