Information Technology Reference
In-Depth Information
does not need to run BGP synchronization. This feature is very seldom used in any network
and should be disabled for ISP networks. A more detailed discussion of BGP synchroniza-
tion is provided in Chapter 2, “Understanding BGP Building Blocks.”
Network Addressing Methodology
The focus of this section on network addressing is specific to infrastructure addressing. The
suggested IGP deployment is a single-area design. This provides no area border at which
to aggregate infrastructure addressing. Infrastructure addressing consists of two types of
addressing—loopback addresses and link addresses. These are discussed in the next
sections. You'll then learn more about customer addressing.
Loopback Addressing
The loopback address provides an IP address that is independent of any physical interface.
The router is the only device on the subnet, allowing a /32 to be used for optimal address
efficiency. If IP multicast is deployed, an RP Anycast is used, as described in Chapter 11,
“Multiprotocol BGP and Interdomain Multicast,” and multiple loopback addresses are
configured.
The loopback address that is not used for the RP Anycast should be explicitly configured
as the BGP router ID. This prevents the possibility of BGP infrastructure failure from
duplicate BGP router IDs existing in the network.
Link Addressing
The other aspect of infrastructure addressing is link addressing. The typical backbone
connection is a point-to-point connection, with only two devices in a subnet. The /31 has
been redefined without a network or broadcast address, making both IP addresses in the
subnet usable. You should capitalize on /31 address efficiency when configuring link
addressing.
The scarcity of IP address space and the difficulty of receiving additional allocations from
the assigning authorities introduced the concept of using RFC 1918, or private addressing
for link addresses. However, RFC 1918 specifically states that packets with private address-
ing in either the source or destination address should not be forwarded over interenterprise
links. This means that they should not be forwarded across the Internet. A traceroute
through an ISP using private addressing for infrastructure links generates packets sourced
from private addresses.
If multiple ISPs use private addressing from the same subnets, there is the potential for
configuration mistakes to cause inadvertent denial-of-service attacks. The accidental
redistribution and advertisements of the private infrastructure addressing could interfere
with other ISPs using the same address space for infrastructure addressing.
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