topic Re: BGP route inaccessible in Routing and SD-WAN

BGP route inaccessible

KiranMalla — Tue, 06 Sep 2022 05:23:03 GMT

Hi Team,

I have configured the routers in attached format. I could not able to access the internal networks of R4 router from R1. I could the see the routes advertised in the router but not able to ping.

RTR#1:

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.10.1.2 4 600 103 99 9 0 0 01:34:52 4
192.168.1.2 4 500 100 100 9 0 0 01:34:51 6

Network Next Hop Metric LocPrf Weight Path
*> 172.21.41.0/24 0.0.0.0 0 32768 i
*> 172.21.42.0/24 0.0.0.0 0 32768 i
* i172.21.43.0/24 10.10.2.2 0 100 0 600 i
*> 10.10.1.2 0 0 600 i
* i172.21.44.0/24 10.10.2.2 0 100 0 600 i
*> 10.10.1.2 0 0 600 i
*>i172.21.45.0/24 192.168.1.2 0 100 0 i
*>i172.21.46.0/24 192.168.1.2 0 100 0 i
* i172.21.47.0/24 10.10.2.2 0 100 0 600 i
*> 10.10.1.2 0 600 i
* i172.21.48.0/24 10.10.2.2 0 100 0 600 i
*> 10.10.1.2 0 600 i

Please help me on how to access the networks 172.21.47.0/24 & 172.21.48.0/24 from R1.

Re: BGP route inaccessible

Georg Pauwen — Mon, 05 Sep 2022 16:34:27 GMT

Hello,

are you announcing both networks on R4 ? Post the full running config of R4...

Re: BGP route inaccessible

balaji.bandi — Tue, 06 Sep 2022 05:24:14 GMT

Can you post BGP config also

show ip bgp

output from all routers ?

Re: BGP route inaccessible

Harold Ritter — Tue, 06 Sep 2022 05:28:22 GMT

Hi @KiranMalla ,

The issue is that R1 does not know how to reach

next hop 10.10.2.2

On R2, You need to configure

next-hop-self

towards R1.

router bgp 500

neighbor 192.168.1.1 next-hop-self

Regards,

Re: BGP route inaccessible

KiranMalla — Mon, 05 Sep 2022 17:50:34 GMT

Hi All, Thanks for your time and replies. Here are the details request. @Harold Ritter I have tried the option but still no luck. I am not sure this is correct design, I have designed for learning and found this issue. R1 is not directly connected to R4 and there is no neighbor-ship to R4. Let me know if any outputs required.

Re: BGP route inaccessible

Harold Ritter — Tue, 06 Sep 2022 05:30:57 GMT

Hi @KiranMalla ,

Next-hop-self

is actually not needed towards R4 as it is an ebgp session. My bad.

Regards,

Re: BGP route inaccessible

KiranMalla — Tue, 06 Sep 2022 05:32:04 GMT

Hi @Harold Ritter , I have issued the command and still not working.

ASR-JS-02#sh run | sec bgp
router bgp 500
no synchronization
bgp log-neighbor-changes
network 172.21.45.0 mask 255.255.255.0
network 172.21.46.0 mask 255.255.255.0
neighbor 10.10.2.2 remote-as 600
neighbor 10.10.2.2 next-hop-self
neighbor 192.168.1.1 remote-as 500
neighbor 192.168.1.1 next-hop-self
no auto-summary
ASR-JS-02#

Re: BGP route inaccessible

Harold Ritter — Mon, 05 Sep 2022 18:15:31 GMT

Hi @KiranMalla ,

Can you please let us know exactly what is not working.

Regards,

Re: BGP route inaccessible

KiranMalla — Tue, 06 Sep 2022 05:34:47 GMT

Hi @Harold Ritter , I am on R1 and trying to ping the loopback interface's configured on R4 i.e., 172.21.47.1 & 172.21.48.1.

ASR-JS-01#sh ip bgp 172.21.47.1
BGP routing table entry for 172.21.47.0/24, version 11
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
1
600
10.10.1.2 from 10.10.1.2 (172.21.44.1)
Origin IGP, localpref 100, valid, external, best
600
192.168.1.2 from 192.168.1.2 (172.21.46.1)
Origin IGP, metric 0, localpref 100, valid, internal
ASR-JS-01#
ASR-JS-01#ping 172.21.47.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.21.47.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
ASR-JS-01#

Re: BGP route inaccessible

Harold Ritter — Tue, 06 Sep 2022 05:35:42 GMT

Hi @KiranMalla ,

R4 only knows about R1 loopback interface IP addresses. You nered to souce the ping from 172.21.41.1 or 172.21.42.1 for it to work.

Ping 172.21.47.1 source 172.21.41.1

Regards,

Re: BGP route inaccessible

MHM Cisco World — Tue, 06 Sep 2022 05:38:10 GMT

Freind you must use

source

in your ping command

The

source

must be know from the router you ping

Re: BGP route inaccessible

KiranMalla — Tue, 06 Sep 2022 05:37:18 GMT

Thank you so much @Harold Ritter for the clarification. I am able to ping now with the

source

command. Thanks for your time on helping me to understand.

Re: BGP route inaccessible

Harold Ritter — Mon, 05 Sep 2022 19:14:07 GMT

You are very welcome @KiranMalla

Re: BGP route inaccessible

KiranMalla — Tue, 06 Sep 2022 10:22:00 GMT

Hi @Harold Ritter , One more design I come up. I have deleted the eBGP between R2 & R4 now. and added the next-hop self on R2 to towards R1 and on R4 towards R3. Now I cant ping the networks in R4 from R1 using source. Any idea why it is not able to ping.

Re: BGP route inaccessible

MHM Cisco World — Tue, 06 Sep 2022 11:20:25 GMT

do hard reset and try again,
hard reset

clear ip bgp x

Re: BGP route inaccessible

Harold Ritter — Tue, 06 Sep 2022 14:23:12 GMT

Hi @KiranMalla ,

You need to check routes received via iBGP to make sure they are not considered "inaccessible". Since R3 advertises routes received from R1 to R4, you need to have next-hop-self configured there too.

Regards,

Re: BGP route inaccessible

KiranMalla — Wed, 07 Sep 2022 02:27:24 GMT

Hi @Harold Ritter , thank you for the clarification. I have configured next-hop self on R1 to R2 & R3 to R4 and it is started reaching the remote networks. Do we have any rules to identify where we need to write these next-hop-self in case we have multiple routers on the network ?

Re: BGP route inaccessible

Harold Ritter — Wed, 07 Sep 2022 13:19:59 GMT

Hi @KiranMalla ,

The general rule is that you need to use next-hop-self command whenever you advertise prefixes received from an eBGP neighbor to an iBGP neighbor, unless you redistribute the subnet used for eBGP in your IGP.

Regards,