Hi Rene,
Firstly I appreciate your knowledge and skills to explain topics in easy way.
My question is we are observing two paths to reach network 4.4.4.4 on R3 router and just one path from R2. Both of them are just one hop away so why this difference is seen in two outputs. Please reply to this question…
Hi Sachin,
The answer is in the output of R1:
R1#show ip bgp
BGP table version is 2, local router ID is 192.168.13.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* 4.4.4.4/32 192.168.13.3 0 3 4 i
*> 192.168.12.2 0 2 4 i
It has installed R2 as the best path to get to 4.4.4.4, so it doesn’t advertise the route through 192.168.13.3 to R2.
Rene
Hi Rene,
Thank you for the lesson. I set up your topology and ran the configuration but the routers did not learn BGP route until i added the command “Network x.x.x.x Mask x.x.x.x” for each router for connecting network. Is it suppose to be so?
Hello Aduma
Yes, that is the case. Notice in Rene’s initial configuration, the routers become BGP neighbors but there is only a single route being advertised between the four routers, that is the 4.4.4.4 network on R4. If you go into all the BGP tables of all the routers, only that route will be indicated.
So unless you explicitly configure the network command, no routes will be advertised.
I hope this has been helpful!
Laz
Thanks Laz, your explanation is helpful.
Hi Rene, i have also the same question, could you please explain
Hello Samit and Tejashri
This is a very good question. That’s why I labbed this one up and in the routers that I set up, it seems that R1, R2 and R3 all have two routes to the destination. I don’t see why R2 should only have one route. I’ll ask Rene to take a look at this one and if needed, the lesson can be modified appropriately.
Thanks for bringing it up!
Laz
Hello @samit.nsn @tejashreedeshmukh021 @lagapidis,
It makes sense why R2 only has one route. Let’s take a look:
R1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
* 4.4.4.4/32 192.168.13.3 0 3 4 i
*> 192.168.12.2 0 2 4 iR1 has two paths, one through R2 and another one through R3. The one through R2 is installed so that’s why R1 never advertises the path through R3 to R2:
R1#show ip bgp neighbors 192.168.12.2 advertised-routes
Network Next Hop Metric LocPrf Weight Path
*> 4.4.4.4/32 192.168.12.2 0 2 4 i
Total number of prefixes 1 You can test this by changing the weight so R1 prefers R3:
R1(config)#route-map PREFER_R3 permit 10
R1(config-route-map)#set weight 1000
R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.13.3 route-map PREFER_R3 inR1 now uses R3:
R1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 4.4.4.4/32 192.168.13.3 1000 3 4 i
* 192.168.12.2 0 2 4 iThe path through R3 is installed and R1 advertises it to R2:
R1#show ip bgp neighbors 192.168.12.2 advertised-routes
Network Next Hop Metric LocPrf Weight Path
*> 4.4.4.4/32 192.168.13.3 1000 3 4 iR2 has it now:
R2#show ip bgp
Network Next Hop Metric LocPrf Weight Path
* 4.4.4.4/32 192.168.12.1 0 1 3 4 i
*> 192.168.24.4 0 0 4 iI hope this helps!
Rene
hi René and staff,
this is a basic question about this lesson (sorry)
Using looking glass servers, I don’t understand how you could filter the routes with | exclude *
What symbol did you use ?
Thanks
Hello Dominique
You are correct that this should not work. This is because the ‘*’ character is a special character used in regular expressions and cannot be used as a single character pattern to be searched for and found. In order to make it work, you must precede each character with a backslash ‘’. The command would work if you entered
show ip bgp | exclude \*
More details about this syntax can be found on the second page of the following Cisco documentation:
I will let Rene know to revise the lesson appropriately.
Thanks for bringing this to our attention!
Laz
Hi Dominique,
I did the exclude example in my lesson on a Cisco router where the exclude parameter looks for a string. The looking glass server you used requires a regular expression and in that case, you need to ignore the * with a slash like @lagapidis explained.
On a Cisco router, you can also use regex but you have to specify it like this:
route-server.ams2>show ip bgp regexp \*Hope this helps!
Rene
Thanks a lot Rene and Laz to spend time in replying me,
I am playing with looking glass servers and show ip bgp regexp \* don’t work as show ip bgp | exclude \*
Hi Rene,
I tried to lab your given example, I would like to confirm with you why 4.4.4.4 is not reachable in R1? Even I tried to advertised 192.168.24.0/24 in R2 and 192.168.34.0/24 in R3.
Best Regard,
Fritz Macahilig
Network Diagram
Hi,
i am not Rene neither his staff, but i think
to understand your question, you will have to put the configs of the routers in your lab (not only the network diagram)
Then I’ll try to answer
Regards
Hello Dominique,
Are you still having issues with this? Like you mentioned, regex for BGP only works for AS numbers:
route-views.optus.net.au>show ip bgp regexp ?
LINE A regular-expression to match BGP AS paths. Use "ctrl-v ?" to enter "?"If you want to filter anything else then you should use the “include” command instead. You can also use regex for the include command. For example:
route-views.optus.net.au>show ip bgp | include _10_
* 1.0.0.0/24 203.13.132.7 10 0 7474 4826 13335 i
* 202.139.124.130 10 0 7474 4826 38803 56203 i
* 202.139.124.130 10 0 7474 4826 38803 56203 iThe example above applies regex to the entire output of the show command. You can get pretty creative with that.
The things you can do a on a looking glass server are limited. On your own routers, you can also combine show ip bgp with a route-map if you want to see specific things:
show ip bgp route-map ?
WORD A route-map to match onDoes this help?
Rene
Hi Fritz ,
Did you use my exact configs? If not, it’s best to paste the output of your BGP tables here.
Rene
Basically, R4 doesn’t have the R1’s interface subnets in its routing table. In order to make it work, you will have to advertise the network interfaces of R1 into BGP.
R1(config)#router bgp 1
R1(config-router)#network 192.168.12.0 mask 255.255.255.0
R1(config-router)#network 192.168.13.0 mask 255.255.255.0
Now ping from R1, it should work.
Hi,
On NXOS9kv ive configured eBGP to multipath up to 2 spines.
leaf1# sh run bgp
!Command: show running-config bgp
!Time: Thu Jun 27 09:53:11 2019
version 7.0(3)I7(1)
feature bgp
router bgp 64521
router-id 3.3.3.3
address-family ipv4 unicast
network 172.16.1.0/24
maximum-paths 2
neighbor 1.1.1.1
remote-as 64520
description eBGP peer spine1
update-source loopback0
ebgp-multihop 2
address-family ipv4 unicast
send-community
next-hop-self
neighbor 2.2.2.2
remote-as 64520
description eBGP peer spine2
update-source loopback0
ebgp-multihop 2
address-family ipv4 unicast
send-community
next-hop-self
However can you confirm why the bgp table shows a blank entry by the network like so,
Thanks,
Hello Rick
If I understand your question correctly, you are asking why the value under the Network column is empty, where you have placed the blue box correct? If that is the case, then when the BGP table has a blank in the network section, what this means is that the network is the same as the one above it. In this case, it is showing that to get to network 172.16.2.0/24 you have either a next hope of 1.1.1.1 or 2.2.2.2. If there was a third choice to reach that network, it would appear below in the next line with an empty Network entry, showing another Next Hop value.
Take a look at this lesson that details this information more fully.
I hope this has been helpful!
Laz
Hi,
If in the BGP Table the best path failed, how it select the second best path ?
