eBGP Multihop with Secondary Addressing

From: Dennis J. Hartmann (dennisjhartmann@hotmail.com)
Date: Tue Jun 21 2005 - 12:19:38 GMT-3


    Why is eBGP required for a peering session between two external BGP
peers when using secondary addressing on the interfaces. Even though the
primary addresses on the interfaces are in different subnets, I'm able to
get a peering relationship up with no prolem, but the lab answer says that
eBGP multihop should be used. Below is the basic IP configuration. Notice
that the primary and secondary address subnets do not align.
 
R1:
172.16.31.0 primary
172.16.13.0 secondary
router bgp 100
neighbor 172.16.13.1 remoate-as 300
 
 
R3:
172.16.13.0 primary
172.16.31.0 secondary
router bgp 300
neighbor 172.16.31.1 remote-as 100
 
show ip bgp summary verified that the neighbors are established and prefixes
are being learned.

Sincerely,

 

Dennis J. Hartmann

White Pine Communications

dh8@pobox.com

CCSI#23402/CCIP/CCNP/CCDP/CCNA/CCDA

Cisco IP Voice Support & Design Specialist

Cisco Optical, VPN & IDS Specialist

MCSE



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