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of one of the directly connected border routers. The border routers in
each major location and remote connectivity hub routers should have the
default route in the BGP table with an AS_PATH of 65100 65105.
Verify that the number of prefixes in BGP is approximately the same as
in EIGRP. Also, save the output from show ip route summary on each
of the core routers and border routers. This will be used for further
validation after the cutover to the BGP core has been made.
Step 3
BGP Core Activation
This step activates the BGP core from a packet-switching perspective. The intent is to
segment the network into separate EIGRP domains by breaking the EIGRP adjacency
formation over the Ethernet DMZ in each location. To accomplish this, on all the routers,
R1 through R13, configure passive interface under the EIGRP router process for the
interface connecting to the Ethernet DMZ in that location. It is important to verify full
connectivity after EIGRP and BGP have reconverged.
Collect the output from show ip route summary on each of the core routers and border
routers. Compare the number of routes in the combined EIGRP and BGP processes with
those collected before breaking the EIGRP adjacencies. The total number of routes in the
tables on these routers should be the same. This validates that full routing information is
received.
The distribution of routes between EIGRP and BGP will vary from location to location. The
core routers will be almost entirely BGP routes. The border routers will be a combination,
depending on how many routes are originated in that location being in EIGRP and the
prefixes originated elsewhere being in BGP.
Final Cleanup
The final step in the migration is to clean up artifacts from the migration. After full connec-
tivity has been verified, the administrative distance for BGP should be returned to the default
values by removing the distance command from the BGP router process configuration. The
clear ip route command must be issued for the new administrative distance to take effect.
The last step is to renumber the core EIGRP process. This can be accomplished by config-
uring an identical EIGRP process with a different ASN on each core router. The old EIGRP
process can then be removed. The old EIGRP process should not be removed until the new
EIGRP process has been configured on every core router and proper adjacency establish-
ment has been confirmed using the show ip eigrp neighbor command.
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