Cisco ASR 9000 Series Routing Configuration Guide

IPv6 uRPF Support on Cisco ASR 9000's A9K-SIP-700
Unicast IPv6 Reverse Path Forwarding (uRPF) mitigates problems caused by the introduction of malformed
or spoofed IP source addresses into a network by discarding IP packets that lack a verifiable IP source address.
Unicast RPF does this by doing a reverse lookup in the Cisco Express Forwarding (CEF) table. Therefore,
uRPF is possible only if CEF is enabled on the router.
Use the ipv6 verify unicast source reachable-via {any | rx} [allow-default] [allow-self-ping] command in
interface configuration mode to enable IPV6 uRPF.
For more information on IPv6 uRPF, refer Implementing Cisco Express Forwarding module in Cisco ASR 9000
Series Aggregation Services Router IP Addresses and Services Command Reference
Remove and Replace Private AS Numbers from AS Path in BGP
Private autonomous system numbers (ASNs) are used by Internet Service Providers (ISPs) and customer
networks to conserve globally unique AS numbers. Private AS numbers cannot be used to access the global
Internet because they are not unique. AS numbers appear in eBGP AS paths in routing updates. Removing
private ASNs from the AS path is necessary if you have been using private ASNs and you want to access the
global Internet.
Public AS numbers are assigned by InterNIC and are globally unique. They range from 1 to 64511. Private
AS numbers are used to conserve globally unique AS numbers, and they range from 64512 to 65535. Private
AS numbers cannot be leaked to a global BGP routing table because they are not unique, and BGP best path
calculations require unique AS numbers. Therefore, it might be necessary to remove private AS numbers from
an AS path before the routes are propagated to a BGP peer.
External BGP (eBGP) requires that globally unique AS numbers be used when routing to the global Internet.
Using private AS numbers (which are not unique) would prevent access to the global Internet. The remove
and replace private AS Numbers from AS Path in BGP feature allows routers that belong to a private AS to
access the global Internet. A network administrator configures the routers to remove private AS numbers from
the AS path contained in outgoing update messages and optionally, to replace those numbers with the ASN
of the local router, so that the AS Path length remains unchanged.
The ability to remove and replace private AS numbers from the AS Path is implemented in the following
ways:
•
The remove-private-as command removes private AS numbers from the AS path even if the path
contains both public and private ASNs.
•
The remove-private-as command removes private AS numbers even if the AS path contains only private
AS numbers. There is no likelihood of a 0-length AS path because this command can be applied to eBGP
peers only, in which case the AS number of the local router is appended to the AS path.
•
The remove-private-as command removes private AS numbers even if the private ASNs appear before
the confederation segments in the AS path.
•
The replace-as command replaces the private AS numbers being removed from the path with the local
AS number, thereby retaining the same AS path length.
The feature can be applied to neighbors per address family (address family configuration mode). Therefore,
you can apply the feature for a neighbor in one address family and not on another, affecting update messages
on the outbound side for only the address family for which the feature is configured.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Implementing BGP
IPv6 uRPF Support on Cisco ASR 9000's A9K-SIP-700

Cisco ASR 9000 Series Specifications

General

Brand	Cisco
Model	ASR 9000 Series
Category	Network Router
Language	English