Problem with BGP routing

[EAleg]

Hi guys, i dont know, but why i cannot ping R2 from RR (30.30.30.2 network or loopback), if RR knows about R2?

I shutdown on RR int gig 0/0.

Maybe i forgot type another command? Thank you for attention and answer.

R4

router bgp 300
bgp log-neighbor-changes
network 4.4.4.4 mask 255.255.255.255
network 11.11.11.0 mask 255.255.255.252
network 30.30.30.0 mask 255.255.255.252
neighbor 2.2.2.2 remote-as 300
neighbor 2.2.2.2 update-source Loopback0
neighbor 5.5.5.5 remote-as 300
neighbor 5.5.5.5 update-source Loopback0
neighbor 11.11.11.2 remote-as 300
neighbor 30.30.30.2 remote-as 300

RR

router bgp 300
bgp log-neighbor-changes
network 5.5.5.5 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 300
neighbor 2.2.2.2 update-source Loopback0
neighbor 4.4.4.4 remote-as 300
neighbor 4.4.4.4 update-source Loopback0
neighbor 11.11.11.1 remote-as 300
neighbor 11.11.11.1 update-source Loopback0
neighbor 70.70.70.1 remote-as 300

R2

router bgp 300
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
neighbor 4.4.4.4 remote-as 300
neighbor 4.4.4.4 update-source Loopback0
neighbor 5.5.5.5 remote-as 300
neighbor 5.5.5.5 update-source Loopback0
neighbor 30.30.30.1 remote-as 300
neighbor 70.70.70.2 remote-as 300

[Giuseppe Larosa]

Hello @EAleg ,

there are three important notes about your iBGP configuration :

a)   you should run an IGP to advertise loopback addresses for example OSPF having OSPF RID = BGP RID = loopback address. this will allow you to deal with single link failures. OSPF should run on all links between routers.

b) You should use only iBGP sessions terminated on loopbacks you have a mix of sessions on loopbacks and sessions on physical interfaces. This is not good. You need to be consistent and to use loopbacks as BGP endpoints with an IGP running as explained in previous point.

c) client to client iBGP sessions are not strictly needed when using Route Reflector servers in real world it is better to have two RRS serving the same set of clients ( many devices this is called a cluster) avoiding direct iBGP sessions between clients otherwise the RRS provides just a backup path.

Edit:

>> I shutdown on RR int gig 0/0.

>> why i cannot ping R2 from RR (30.30.30.2 network or loopback), if RR knows about R2?

RR : gi0/0 is the interface towards R2 looking at your network diagram.

R4 cannot propagate to R2 any  BGP info learned by RR on the direct iBGP session to R2 for the iBGP split horizon rule in other words R2 is not a route reflector client of R4.

There is an IGP running in your network or not ?

Hope to help

Giuseppe

[EAleg]

Hi, thank You Giuseppe for answer, in order:

1. What do You mean by this "you should run an IGP to advertise loopback addresses for example"? I thought this command do this network 4.4.4.4 mask 255.255.255.255

2. "You should use only iBGP sessions terminated on loopbacks you have a mix of sessions on loopbacks and sessions on physical interfaces" - Yes, first of all i must establish connection between two routers, i mean on physical interfaces. But, i dont know, how i must do, that the Routers (example R2 and R4)can speak between themselves using loopback.

3. I have not yet configured this router as Route Reflector >_<. I gave him such a name, sorry.

But, i dont understand, why i cannot pinging R2, if RR and R4 knows about all network?

[Giuseppe Larosa]

Hello @EAleg ,

attempting to use iBGP without an underlying IGP is challenging and not recommended.

>> 1. What do You mean by this "you should run an IGP to advertise loopback addresses for example"? I thought this command do this network 4.4.4.4 mask 255.255.255.255

No, I mean that iBGP checks the BGP next-hop and for example a BGP advertisement like the following:

4.4.4.4/ 32 via BGP next-hop 4.4.4.4  cannot be used . The BGP next-hop must be different from the prefix and it must be in the routing table by methods that are indipendent of BGP protocol otherwise for example you can end up with some race conditions where an iBGP session can be established only if another one is already established.

Running an IGP means adding a routing process like

router ospf 10

network 0.0.0.0 255.255.255.255 area 0

to advertise your loopbacks. This provides an indipendent way to learn other routers loopbacks avoiding race conditions.

>> 2. "You should use only iBGP sessions terminated on loopbacks you have a mix of sessions on loopbacks and sessions on physical interfaces" - Yes, first of all i must establish connection between two routers, i mean on physical interfaces. But, i dont know, how i must do, that the Routers (example R2 and R4)can speak between themselves using loopback.

if you use an IGP like OSPF underlying you don't need those iBGP sessions on physical interfaces but you just need iBGP sessions on loopbacks. 

Test it in your lab. You will see a better and clear environment that will be able to support a single link failure with no issues.

Hope to help

Giuseppe

[balaji.bandi]

we need to know the routing table, on RR how this is learning.

Try - (not sure if this fix the issue?)

neighbor x.x.x.x  next-hop-self

[MHM Cisco World]

try ping 30.30.30.1 from RR is it success ?

[EAleg]

Thank for answer, yes, is it success.

[Giuseppe Larosa]

Hello @EAleg ,

so RR can ping 30.30.30.1 that is on R4. But what source IP address are you using ?

if RR uses 11.11.11.2 R2 should be able to answer as it should have a route to 11.11.11.0/30 via 30.30.30.1

if RR uses its own loopback as source R2 cannot reply as it doesn't know RR's loopback 4.4.4.4 anymore, because R4 cannot pass prefix 4.4.4.4/32 to R2 another iBGP peer having received it on an iBGP session.

Hope to help

Giuseppe

[MHM Cisco World]

since the RR can ping .1 not .2 then the issue is R2, where the return back traffic is drop. check the R2 see if IP of source of ping is reachable or not.

[paul driver]

Hello

R4
router bgp 300
no neighbor 11.11.11.2 remote-as 300

RR
router bgp 300
neighbor 30.30.30.1 remote-as 300
neighbor 30.30.30.1 route-reflector client
neighbor 11.11.11.1 route-reflector client

R2
router bgp 300
no neighbor 30.30.30.2 remote-as 300