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6.1.8 Secondary Addressing – 29 Bit
This approach utilizes a 29-bit subnet for each remote connection. Within each 29-bit subnet is the POP router secondary, the Black
Box WAN addressing, and the remote router secondary.
6.1.9 Pros and Cons of Different IP Addressing Schemes
The following table provides information about addressing scheme pros and cons.
Table 10 Addressing Schemes: Pros and Cons
6.1.10 Routing Considerations for IP Multiplexing
RIP / RIP2 / IGRP –Turn off split horizons to enable routing updates through secondary addresses, if used.
EIGRP – Updates are sourced only from primary addresses, although routers will listen to updates arriving on primary and
secondary.
OSPF – For Cisco and other routers, routing updates are sourced and detected only on primary addresses, therefore
secondary addressing schemes are not usable.
BGP4 – Routing updates are fully functional over primary and secondary addresses.
POP Router e0: 200.1.1.1/30 primary
199.1.1.1/29 secondary
199.1.1.9/29 secondary
199.1.1.17/29 secondary
POP Black Box e0:
wan1:
wan2:
wan3:
200.1.1.2/30
199.1.1.2/29
199.1.1.10/29
199.1.1.18/29
Black Box 1 e0:
wan
201.1.1.2/30
199.1.1.3/29
Router 1 e0: 201.1.1.1/30 primary
199.1.1.4/29 secondary
Black Box 2 e0:
wan1:
202.1.1.2/30
199.1.1.11/29
Router 2 e0: 202.1.1.1/30 primary
199.1.1.12/29 secondary
Router/DSU s0: 199.1.1.19/29
Approach Pros Cons
Single Subnet Minimizes consumption of IP
address space
POP Black Box requires two route statements
per remote connection.
Split Subnet Less routes required in Black
Box
Consumes 29-bit subnet per remote site.
Secondary Addressing Easily Scalable Consumes 29-or 30-bit subnet per remote. Not
transparent to certain routing protocols.