Information Technology Reference
In-Depth Information
Example 4-15
Advertisement Status in R1 Under Normal Conditions
R1#show ip bgp 172.16.2.0
BGP routing table entry for 172.16.2.0/24, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
192.168.12.2
300
192.168.13.3 from 192.168.13.3 (192.168.13.3)
Origin IGP, metric 0, localpref 100, valid, external, best
Community: 100:300
R1#show ip bgp neighbor 192.168.12.2 | include Condition-map
Condition-map AS300-in, Advertise-map AS200-out, status: Withdraw
Example 4-16
R2 Does Not Have 172.16.1.0 Under Normal Conditions
R2#show ip bgp 172.16.1.0
% Network not in table
When the session between R1 and R3 is down, 172.16.2.0/24 is removed from R1's BGP
RIB. R2's advertisement status is now Advertise, as shown in Example 4-17. The prefix
172.16.1.0/24 is now available in R2, as shown in Example 4-18. For this design to work,
it is important to ensure that the right prefix from the provider is being tracked.
Example 4-17
Advertisement Status During Primary Link Failure
R1#show ip bgp neighbor 192.168.12.2 | include Condition-map
Condition-map AS300-in, Advertise-map AS200-out, status: Advertise
Example 4-18
Prefix 172.16.1.0 Is Present on R2 During a Primary Link Failure
R2#show ip bgp 172.16.1.0
BGP routing table entry for 172.16.1.0/24, version 14
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Not advertised to any peer
100
192.168.12.1 from 192.168.12.1 (192.168.13.1)
Origin IGP, metric 0, localpref 100, valid, external, best
Figure 4-3 shows a topology of conditional advertisement to track the existence of a prefix.
Within AS 100, R1 is the only BGP speaker, and it has an eBGP session with R3 in AS 300.
All routers within AS 100 communicate using OSPF. The internal address block 10.0.0.0/
16 is translated into a public block 172.16.0.0/16 on R2. The policy is that R1 should not
advertise 172.16.0.0/16 to R3 unless 10.0.0.0/16 is available.
