BGP Next Hop Self


(Rene Molenaar) #1

This topic is to discuss the following lesson:


(ammar a) #2

Hi Rene,
Thanks a lot for explaining the next hop self. That was very detailed. I really appreciate it Sir. Also i have a question, what rental lab racks do you recommend? i know there are a lot but what you think is the best and the cheapest?
Thanks

Ammar,
CCIE R&S - in progress


(Rene Molenaar) #3

Hi Ammar,

Hmm the first thing I would look for is what topology they support. If you use the INE workbooks, make sure the rack rental is cabled for their topology AND has all the startup-configs.

Also if possible, check if they are located close to you…a high delay can be annoying since the console will be a bit slow.

Rene


(ammar a) #4

Rene,
Thanks for you advice. Yes, i will start looking soon. As you know written is not interesting as the lab study. I am focusing now on the written to pass it so i can be fully prepared for the lab. Thanks

Ammar,
CCIE R&S - in progress


(Hamood R) #5

Rene,
Great lesson however, I have question. I tried the lab in GNS3 when I make R2 NEXTHOP for R1 and R3. I can see R3 learns about 3.3.3.0/24 network from R2 and it also installs in BGP table.
When I do “sh ip route bgp” I can see 3.3.3.0/24 with next hop of 192.168.12.2.
When I ping from R3 it is not ping-able. As soon as I advertized 192.168.23.0 and 192.168.12.0 on R2 it starts pinging. Hope I am not missing any key stuff from the lesson.
Please advice.
Thanks
Hamood


(Rene Molenaar) #6

Hi Hamood,

R1 will know how to reach 3.3.3.3 but there will be one problem left. R3 doesn’t have a clue how to reach 192.168.12.0 /24.

This is something you’ll have to fix by advertising 192.168.12.0 /24 in BGP on R2.

Rene


(Hamood R) #7

Thank you Rene, I just wanted to confirm.

Hamood


(Shinu V) #8

Hi Rene

Can we install a static route for network 192.168.23.0 on R1 with next hop R2 to reach network 3…3.3.0/24

Will this work?


(Rene Molenaar) #9

Hi Shinu,

It will work, with static routes you can make anything work but it’s not a really scalable solution…you always have to configure things manually.

Rene


(aaron b) #10

issue with BGP

bgp router can ping interface 126.89.120.106 but unable to ping 126.89.120.105 which is on the same router ?

any ideas !


(Rene Molenaar) #11

Hi Aaron,

What do you mean exactly? :slight_smile: Are these two /32 addresses?

Rene


(aaron b) #12

/ 27
when run sh ip route 126.89.120.106 , it has a route to the host but still unable to ping


(Rene Molenaar) #13

See if the router on the other side knows how to reach your network. It’s possible that you can send your packets one way but that they can’t return.


(Ziad K) #14

Rene, can you explain this comment above in bit more detail:
“We use iBGP between R1/R2 and eBGP between R2/R3”

in earlier lessons you said ibgp is eigrp/ospf. but in the config above r1/r2 are directly connected with only bgp configured.
so you are treating bgp as an ibgp then?
or because they are in the same AS, you have to call it internal vs external.


(Rene Molenaar) #15

Hi Ziad,

iBGP is when you run BGP when using the same AS number, eBGP is when we use different AS numbers.

When I refer to OSPF/RIP/EIGRP I talk about IGPs (Interior Gateway Protocols). Don’t mix this up with iBGP :slight_smile:

Rene


(Ziad K) #16

Rene, thanks for the above and i thought i was good to go until i read the local pref section and you mentioned: “I’ll configure OSPF within AS2 to prepare it for IBGP.”
and now i am confused again! why are you calling OSPF IBGP? when it should be IGP.


(Rene Molenaar) #17

Hi Ziad,

When we use IBGP, we typically use loopback interfaces to establish the IBGP neighbor adjacency. To advertise the loopbacks, we use an IGP like OSPF.

Take a look at this lesson, it explains everything:

Rene


(Ganesh D) #18

Hi Rene,

I see BGP doesn’t change the next hop ip for the routes it advertise and the above mentioned solutions would work around the reach-ability issues if needed?
Can you please explain what could be the reason for such an option in design of BGP protocol by default.

Thanks
ganesh


(Rene Molenaar) #19

Hi Ganesh,

Good question, i’m not sure why this is the default behavior. I’ll see if I can find something.

Rene


(Georgi T) #20

hey Rene

when i configure the R2 as a next-hop-self , I can see the R1 has 192.168.12.2 as *> in its routing table but I cant ping the 3.3.3.3 network .but I when advertise the networks in R2 as you explained the first example ,I can ping it easily . Do you have any idea about this problem ?