4.6 Configure and verify single-homed branch connectivity using eBGP IPv4 (limited to peering and route advertisement using Network command only)



Using the above topology we will configure a single homed eBGP. Download lab here.
On ISP1:

router bgp 101
 no synchronization
 bgp log-neighbor-changes
 neighbor remote-as 3
 no auto-summary

On ENT1:

router bgp 3
 no synchronization
 bgp log-neighbor-changes
 neighbor remote-as 101
 no auto-summary

All that is left is to use OSPFv2 to distribute routes from FIREWALL to ENT1.


To verify just use the following “show” commands.

ISP1#show ip bgp neighbors
BGP neighbor is,  remote AS 3, external link
  BGP version 4, remote router ID
  BGP state = Established, up for 00:00:42
  Last read 00:00:42, last write 00:00:42, hold time is 180, keepalive interval is 60 seconds
... <rest of output deleted>
ISP1#show ip route
Codes: 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
Gateway of last resort is not set
B [20/2] via, 00:00:50
C is directly connected, GigabitEthernet0/0
B [20/2] via, 00:00:50
ISP1#show ip protocols
Routing Protocol is "bgp 101"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  IGP synchronization is disabled
  Automatic route summarization is disabled
    Address          FiltIn FiltOut DistIn DistOut Weight RouteMap
  Maximum path: 1
  Routing Information Sources:
    Gateway         Distance      Last Update           20      00:01:24
  Distance: external 20 internal 200 local 200

Perform the same “show” commands on ENT1 to verify association.
Using a ping and traceroute command can check the Layer 3 connectivity for the entire path:

SERV1> ping
84 bytes from icmp_seq=1 ttl=253 time=40.158 ms
84 bytes from icmp_seq=2 ttl=253 time=21.494 ms
84 bytes from icmp_seq=3 ttl=253 time=27.591 ms
84 bytes from icmp_seq=4 ttl=253 time=22.309 ms
84 bytes from icmp_seq=5 ttl=253 time=23.390 ms
SERV1> trace
trace to, 8 hops max, press Ctrl+C to stop
 1   2.539 ms  9.359 ms  9.216 ms
 2   19.470 ms  20.039 ms  19.656 ms
 3   *   39.910 ms (ICMP type:3, code:3, Destination port unreachable)  *

Note the exam topics to not mention troubleshooting. Just configuring and verifying….

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