BGP route advertisement and received routes issue

[KevA]

BGP advertised and received routes issue

Can someone explain to me what I am missing my configuration given the issues below? I have attached devices mentioned below as well as others in the AS-PATH as well as the section of topology relevant to my issue.

Objective:
• R7 and R12 are peering (eBGP) with R200 and must only receive a BGP default route from it.
• R7 and R8 must advertise only a BGP default route to their eBGP neighbors. This default route must only be advertised if a default route is already installed on their routing tables.
• R9 should see the default route from it eBGP neighbors R8 and R23 but route is only being received from R8.

ISSUE #1:

On R7, when I run the command

show ip bgp neighbors 10.0.100.1

advertised-routes I get the following output with Total number of prefixes 0. Shouldn't the total number of prefixes be 1 given when I run

show ip bgp

command I can see the prefix in the bgp table?:

R7#sh ip bgp neighbors 10.0.100.1 advertised-routes
BGP table version is 3, local router ID is 10.1.7.7
<Output omitted for brevity>
Originating default network 0.0.0.0

Network Next Hop Metric LocPrf Weight Path

Total number of prefixes 0

However, I can see the prefix exist in the BGP table:

R7#sh ip bgp
BGP table version is 3, local router ID is 10.1.7.7
<Output omitted for brevity>
RPKI validation codes: V valid, I invalid, N Not found

       Network          Next Hop       Metric    LocPrf     Weight     Path
*>   0.0.0.0            10.1.100.1     0                                         65001 i

ISSUE #2:

R9 should be learning this prefix from both its eBGP neighbors but the prefix is being ignored from R23 because it
is already being received from R8. How do I resolve this issue?

R9#sh ip bgp summary
BGP router identifier 10.2.9.9, local AS number 65002
<Output omitted for brevity>
Neighbor          V     AS          MsgRcvd     MsgSent     TblVer    InQ    OutQ   Up/Down      State/PfxRcd
10.1.100.1      4    65001         278            278            4            0       0         04:03:23         1
10.2.10.10      4    65002         44              46              4            0       0         00:37:00         0
172.16.100.9  4     65000          111              117             4               0        0          01:31:57           0

R9#clear ip bgp * soft
*Dec 8 01:23:24.637 EET: BGP: nbr_topo global 10.1.100.1 IPv4 Unicast:base (0xF5AB8BD8:1) refresh_epoch is 3
*Dec 8 01:23:24.640 EET: BGP(0): 10.1.100.1 rcvd UPDATE w/ attr: nexthop 10.1.100.1, origin i, merged path 65001, AS_PATH
*Dec 8 01:23:24.640 EET: BGP(0): 10.1.100.1 rcvd 0.0.0.0/0...duplicate ignored

[MHM Cisco World]

clear and debug twice and check again 
it not relate to any prefix it relate to BGP table version
MHM

[KevA]

MHM Cisco World,

One of the issues was I had to change R4 next-hop with R23 given R23 now
using the same AS#65000 as R4. Follow the conversation with Harold whereas
he instructed me as to the reason for the issue and how to troubleshoot and
resolve.

I am still not finished with the lab so will let you know if there are any
other issues that come up and I cannot resolve.

Thanks for the responses and help!!

[Harold Ritter]

Hi @KevA ,

> I would imagine then I will still need the route-map local-only configuration that you provided if I

> was to change the AS# on R23 back to AS65111 and should not need the next-hop-self

> configured on R4. 

The config I suggested won't hurt whether R23 is in AS65000 or AS65111. The next-hop-self is not required if R23 is in AS65111, as next-hop-self is the default behavior for eBGP neighbors.

Regards,

[KevA]

Harold,

Thanks for your help and explanations as to probable causes. 

Yes, I mentioned R4 will not need the next-hop-self if this was an eBGP relationship. R23 will not require the next-hop-self  cause like you mentioned, its in a different AS so would be eBGP neighbors which the default behaviour is next-hop-self. 

I still have more tasks to complete in this lab so I will let you know if I get stuck with any other config issues but try to resolve on my own at first. 

Stay tuned and thanks again!!

[Harold Ritter]

Hi @KevA ,

Good luck with the rest of the labs and it will be a pleasure to help you out if you run into any additional issues.

Regards,

[KevA]

Hey Harold,

So far the rest of the lab is going well except two things which I will try
to figure out the other again on my own but the issue below I cannot
resolve.

*ISSUE:* SW7 in Office 1 Network is not learning the default route
originated by any of its neighbors. I included the routing protocols
configs for all the devices in office 1 network.

*SW7#sh run | section router*
r




*outer ospf 1 router-id 10.4.7.7 passive-interface Loopback0 network
10.4.7.7 0.0.0.0 area 0 network 10.4.200.254 0.0.0.0 area 0 network
10.4.201.254 0.0.0.0 area 0*

*SW7#sh ip ospf nei*
Neighbor ID Pri State Dead Time Address Interface
*10.4.11.11 1 FULL/BDR 00:00:31 10.4.201.1 Vlan201*
10.4.12.12 1 FULL/DR 00:00:32 10.4.201.2 Vlan201


*SW7#sh ip route 0.0.0.0% Network not in table*

*R11#sh run | section router*






*router ospf 1 router-id 10.4.11.11 area 10 stub no-summary network
10.4.11.11 0.0.0.0 area 0 network 10.4.201.1 0.0.0.0 area 0 network
10.5.100.11 0.0.0.0 area 10 default-information originate*


*R11#sh ip ospf nei*
Neighbor ID Pri State Dead Time Address Interface
*10.4.7.7 1 FULL/DROTHER 00:00:35 10.4.201.254
Ethernet0/0*
10.4.12.12 1 FULL/DR 00:00:37 10.4.201.2
Ethernet0/0


*R11#sh ip route 0.0.0.0Routing entry for 0.0.0.0/0 <>,
supernet*
Known via "bgp 65001", distance 200, metric 0, candidate default path
Tag 20000, type internal
Last update from 10.4.12.12 04:34:00 ago
Routing Descriptor Blocks:
** 10.4.12.12, from 10.4.12.12, 04:34:00 ago*
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 20000
MPLS label: none


*R12#sh run | section router*



*router ospf 1 router-id 10.4.12.12 network 10.4.12.12 0.0.0.0 area
0 network 10.4.201.2 0.0.0.0 area 0*

R12#sh ip ospf nei
Neighbor ID Pri State Dead Time Address Interface

*10.4.7.7 1 FULL/DROTHER 00:00:38 10.4.201.254
Ethernet0/010.4.11.11 1 FULL/BDR 00:00:38 10.4.201.1
Ethernet0/0*



*R12#sh ip route 0.0.0.0Routing entry for 0.0.0.0/0 <>,
supernet*
Known via "bgp 65001", distance 20, metric 0, candidate default path
Tag 20000, type external
Last update from 200.1.100.5 04:35:35 ago
Routing Descriptor Blocks:
* 200.1.100.5, from 200.1.100.5, 04:35:35 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 20000
MPLS label: none

[KevA]

Harold,

I shutdown the interfaces that connect the routers to SW7 to restart the
ospf process and now I can see the default route on SW7.

*SW7#sh ip route | inc O*E2 E1 - OSPF external type 1, E2 - OSPF
external type 2O*E2 0.0.0.0/0 <> [110/1] via 10.4.201.1,
00:03:36, Vlan201*

*KevA*

[MHM Cisco World]

Issue 2 is difficult

There is config make next-hop of both prefix same 

So one of router either use route-map to change next-hop or it router-server (router server dont modify the next hop) or it use next-hop unchanged.

These case can make your router duplicate.

MHM

[KevA]

R8 and R23 forms eBGP neighborship with R9 and neither of them has the next-hop-self configured for the neighborship with R9.

[MHM Cisco World]

Can I see config if it lab?

MHM

[KevA]

I attached the configs and topology snapshot for the devices in the original post. 

[MHM Cisco World]

There is no attachment 

MHM

[KevA]

I will attach again. Let me know if you receive them. 

[MHM Cisco World]

Send my as private message 

MHM

[M02@rt37]

Hello @KevA 

For issue 1, check the

route-map on R7 with its neighbor 10.0.100.1. Route-map

applied in outboud.

For issue 2, add

 maximum-path ebgp 2 

command under router bgp process on R9.