eBGP host cant Communicate eBGP Host over iBGP mesh

[TangoAlfa]

Hi All,

Refer to the diagram Host-A can communicate Host-B and Host-C can communicate with Host-D but Host-A and Host-B can not communicate with Host-C and D. Where as every where route is available.

NOTE:

From R-3 and 4 I can reach Host-C and D

From R-1 and 2 I can reach Host-A and B

Please refer attached diagram.

[MHM Cisco World]

This other issue, 

For first one did you clear

 ip bgp x 

and test again?

[TangoAlfa]

I have done

clear ip bgp *

But not solving

[TangoAlfa]

Router config and

show 

command attached.

[MHM Cisco World]

please in 

10.10.10.10 do trace to 172.16.1.10 host

share the trace here 
you config is OK as I see

[TangoAlfa]

Hi MHM,

I am bit surprise from host I am able to reach each other host but from router I cant. I observed during your trace collection. Please check attached snap.

[MHM Cisco World · Accepted solution]

Yes as I mention before you config is correct, 
Now you can ping/trace from host to host 
BUT why router can not ? because in router you need to add source to ping/trace, this source must know from all router in path to destination. 

[paul driver]

Hello
Your configuration is NOT correct @MHM Cisco World  as you do not show any IGP or static routing, as such the bgp is failing due to lack of NLRI . 
As i have stated previously you need to provide a underlay transit network for next hop reachability for full mesh ibgp something that seems to missing in the cfg files you have posted.

[TangoAlfa]

Hi Paul,

Thanks for your reply. You mean in the iBGP mesh I have to configure default route as well? if yes then shall I put each router under the iBGP mesh? where to put? Please guide me

[paul driver]

Hello

---

@TangoAlfa wrote:

Hi Paul,

Thanks for your reply. You mean in the iBGP mesh I have to configure default route as well? if yes then shall I put each router under the iBGP mesh? where to put? Please guide me

---

No.. I mean you need a internal routing process like ospf/eigrp (IGP) to advertsie the transit networks, something you do not have at this time

example:
rtr1-4
router eigrp 100
no auto-summary
network 0.0.0.0 0.0.0.0

[MHM Cisco World]

if he direct connect and use cross connect between iBGP he dont need any IGP.

[TangoAlfa]

My iBGP mesh is cross connect(refer:diagram)

[paul driver]

Hello

---

@MHM Cisco World wrote:

if he direct connect and use cross connect between iBGP he dont need any IGP.

---

How is reachability made to all IBGP rtrs in a full mesh without any static routing or IGP?
The IBGP rtrs may know where to go but probably won’t have the correct information how to get there, also Split horizon wont allow IBGP learned routes to be advertised to another ibgp peer. So this is where IGP comes into play, it will provide that reachability 

In essence its recommended to run an igp, Additionally the peering is usually made with loopbacks as well..