eBGP and iBGP simple topology

esr0159

I came across this topology on the FLG Route book.



I did configure the bgp for all routers, but I'm having problems reaching network from R1 to R3 and vice versa.
On R1 I'm advertising 209.165.200.224/27
On R3 I'm advertising 192.168.33.0/24

Any help is very much appreciated thanks!


R1#ping 192.168.33.1


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.33.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

R3#ping 209.165.200.225


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 209.165.200.225, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)








========R1 config / show ip route / show ip bgp sum===========


R1#show run | sec router bgp
router bgp 65100
no synchronization
bgp log-neighbor-changes
network 209.165.200.224 mask 255.255.255.224
neighbor 192.168.2.2 remote-as 65000
neighbor 192.168.2.2 ebgp-multihop 255
neighbor 192.168.2.2 update-source Loopback0
no auto-summary

Gateway of last resort is not set


192.168.2.0/32 is subnetted, 1 subnets
S 192.168.2.2 [1/0] via 209.165.202.130
B 192.168.22.0/24 [20/0] via 192.168.2.2, 00:00:09
B 192.168.33.0/24 [20/0] via 192.168.2.2, 00:00:09
209.165.200.0/24 is variably subnetted, 2 subnets, 2 masks
C 209.165.200.224/27 is directly connected, Loopback1
L 209.165.200.225/32 is directly connected, Loopback1
209.165.201.0/32 is subnetted, 1 subnets
C 209.165.201.1 is directly connected, Loopback0
209.165.202.0/24 is variably subnetted, 2 subnets, 2 masks
C 209.165.202.128/30 is directly connected, FastEthernet0/1
L 209.165.202.129/32 is directly connected, FastEthernet0/1

R1#show ip bgp sum
BGP router identifier 209.165.201.1, local AS number 65100
BGP table version is 4, main routing table version 4
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/3 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 912 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs


Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.2.2 4 65000 6 5 2 0 0 00:01:27 2


========R2 config / show ip route / show ip bgp sum===========


R2#show run | sec router bgp
router bgp 65000
no synchronization
bgp log-neighbor-changes
network 192.168.22.0
neighbor 192.168.3.3 remote-as 65000
neighbor 192.168.3.3 update-source Loopback0
neighbor 192.168.3.3 next-hop-self
neighbor 209.165.201.1 remote-as 65100
neighbor 209.165.201.1 ebgp-multihop 255
neighbor 209.165.201.1 update-source Loopback0
no auto-summary

R2#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, + - replicated route


Gateway of last resort is not set


172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.23.0/29 is directly connected, FastEthernet0/0
L 172.16.23.2/32 is directly connected, FastEthernet0/0
192.168.2.0/32 is subnetted, 1 subnets
C 192.168.2.2 is directly connected, Loopback0
192.168.3.0/32 is subnetted, 1 subnets
D 192.168.3.3 [90/156160] via 172.16.23.3, 00:02:04, FastEthernet0/0
192.168.22.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.22.0/24 is directly connected, Loopback1
L 192.168.22.1/32 is directly connected, Loopback1
D 192.168.33.0/24 [90/156160] via 172.16.23.3, 00:02:04, FastEthernet0/0
209.165.200.0/27 is subnetted, 1 subnets
B 209.165.200.224 [20/0] via 209.165.201.1, 00:01:10
209.165.201.0/32 is subnetted, 1 subnets
S 209.165.201.1 [1/0] via 209.165.202.129
209.165.202.0/24 is variably subnetted, 2 subnets, 2 masks
C 209.165.202.128/30 is directly connected, FastEthernet0/1
L 209.165.202.130/32 is directly connected, FastEthernet0/1


R2#show ip bgp sum
BGP router identifier 192.168.22.1, local AS number 65000
BGP table version is 5, main routing table version 5
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/3 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 912 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs


Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.3.3 4 65000 6 7 5 0 0 00:02:13 1
209.165.201.1 4 65100 6 7 5 0 0 00:02:15 1







========R3 config / show ip route / show ip bgp sum===========
R3#show run | sec router bgp
router bgp 65000
no synchronization
bgp log-neighbor-changes
network 192.168.33.0
neighbor 192.168.2.2 remote-as 65000
neighbor 192.168.2.2 update-source Loopback0
no auto-summary


R3#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, + - replicated route


Gateway of last resort is not set


172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.23.0/29 is directly connected, FastEthernet0/0
L 172.16.23.3/32 is directly connected, FastEthernet0/0
192.168.2.0/32 is subnetted, 1 subnets
D 192.168.2.2 [90/156160] via 172.16.23.2, 00:02:48, FastEthernet0/0
192.168.3.0/32 is subnetted, 1 subnets
C 192.168.3.3 is directly connected, Loopback0
D 192.168.22.0/24 [90/156160] via 172.16.23.2, 00:02:48, FastEthernet0/0
192.168.33.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.33.0/24 is directly connected, Loopback1
L 192.168.33.1/32 is directly connected, Loopback1
209.165.200.0/27 is subnetted, 1 subnets
B 209.165.200.224 [200/0] via 192.168.2.2, 00:01:54

R3#show ip bgp sum
BGP router identifier 192.168.33.1, local AS number 65000
BGP table version is 5, main routing table version 5
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/3 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 912 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs


Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.2.2 4 65000 8 7 5 0 0 00:02:56 2


=======

atorven

post the output of sh ip bgp

rjon17469

Try:

R1# ping 192.168.33.1 so lo1

esr0159

@atroven
it's posted already.

@rjon17469
woah it works so I'm missing the source command on the ping thanks! R3 can ping R1 with so lo1 now. I thought I messed up my configs on this one.

rjon17469

The next question is, do you understand why it didn't work without the source interface specified? And as an added bonus, try making it work from both R1 and R3 without specifying the source interface.

esr0159

@rjon17469
Yep but I think I still need to go more on the BGP section for the route exam for this one :X.

I was able to make R1 and R3 ping without specifying the source command work by adding the redistribute connected command on R2. Is this solution allowed or is there another way that I'm missing? :

@atroven

I missed your post earlier, here's the sho ip bgp of the routers.

R1

R1#show ip bgp
BGP table version is 12, local router ID is 209.165.201.1
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
*> 192.168.22.0 192.168.2.2 0 0 65000 i
*> 192.168.33.0 192.168.2.2 0 65000 i
*> 209.165.200.224/27
0.0.0.0 0 32768 i



R2
R2#sho ip bgp
BGP table version is 11, local router ID is 192.168.22.1
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
*> 192.168.22.0 0.0.0.0 0 32768 i
r>i192.168.33.0 192.168.3.3 0 100 0 i
*> 209.165.200.224/27
209.165.201.1 0 0 65100 i


R3

R3#show ip bgp
BGP table version is 13, local router ID is 192.168.33.1
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
r>i192.168.22.0 192.168.2.2 0 100 0 i
*> 192.168.33.0 0.0.0.0 0 32768 i
*>i209.165.200.224/27
192.168.2.2 0 100 0 65100 i
R3#

VinnyCisco

Another way I would do it without redistributing the routes is on Router 1 - you can set a default route since there is only one way out.

The problem is that router 1 does not know about the 172.16.13.0 /29 network between R2 and R3. When you used the redistribution, it now injects the connected route.

Great way to see the issue and resolution in action - Run a 'debug ip packet' on Router 1 before you fix it and after. You will see the ping come into Router 1, but show that the destination network as unrouteable. Then after you create the default route on Router 1, repeat the ping and see the difference.

networker050184

In the real world you're likely to be advertising the block your infrastructure is addressed out of so its not a big deal. You're also likely to be doing most of your reach ability testing from non infrastructure blocks.

rjon17469

esr0159 wrote: »

I was able to make R1 and R3 ping without specifying the source command work by adding the redistribute connected command on R2. Is this solution allowed or is there another way that I'm missing?

That's one way to do it, and as you saw it worked fine. Other ways involve specifying a default route on R1/R3, specifying the connected networks under the BGP processes on R1/R3 or R2, redistributing connected routes, static routes, etc.

The more important takeaway is the understanding of why it didn't work - each router had reachability information to the remote loopback address, but not the remote connected interface. When you issue a ping command, the default source address is that of the interface which the packet is leaving, in this case the connected interface. So to make it work you either specify the source address as an address which has reachability from the destination, or you make the connected interface which is used as the source address have reachability from the destination.

These are the types of nuances which Cisco leverages frequently.

esr0159

Hi all,

Thanks for your help for this one. I just really want to mix the eBGP and iBGP for the route studies.

We do work on BGP at work but my current role is only allowed for the neighbor peering (ebGP), and I can't edit the routers at work (or else everything goes down ).

I've been banging my head the past few days (crossing out default routes + redistribution) until I was able to get some advice from the masters here in the forum .

Now I do understand why the route redistribution topic is handled first before the BGP topic.

Thanks again guys, I hope you don't mind if I post other topologies that I'll try to recreate for the route studies.