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36 An Introduction to IP Routing Protocols
Route policies supports the following types of policies:
• Accept (In) Policies
Accept polices are applied to incoming routing updates before they are
applied to the routing table. In the case of RIP, accept policies can be
applied to all incoming packets and only one policy can be created
for each RIP interface. In the case of OSPF, accept policies are only
applied to Type 5 External routes based on the advertising router ID.
There can only be one OSPF accept policy per switch and the policy
is applied before updates are added to the routing table from the link
state database.
• Announce (Out) Policies
Announce policies are applied to outgoing routing updates before
the routing update packets are actually transmitted from the switch.
In the case of RIP, announce policies can be applied to all outgoing
packets and only one policy can be created for each RIP interface.
Announce policies are not supported for OSPF as OSPF requires
routing information to be consistent throughout the OSPF domain.
• Redistribution Policies
Redistribution policies are used to provide notification of addition or
deletion of a route in the routing table by one protocol to another
protocol. OSPF redistribution policies send redistributed routes as Type
5 External routes. There can be only one OSPF redistribution route per
switch and it must be configured as a ASBR with redistribution enabled.
Route policies consist of the following items:
• Prefix Lists
— List of IP addresses with subnet masks.
— Identified by a prefix list name and unique identifier.
— Prefix lists support the comparison of ranges of incoming masks.
• Route Maps
— Contain a set of match and set parameters.
— Match and set parameters can contain several prefix lists.
— A set of match and set parameters are identified by a sequence
number.
— Accept and deny actions are associated with each sequenced
parameter set.
— Sequence numbers act as a preference setting. Sets with a lower
sequence number are preferred over those with a higher sequence
number.
Nortel Ethernet Routing Switch 5500 Series
Configuration-IP Routing Protocols
NN47200-503 03.01 Standard
5.1 27 August 2007
Copyright © 2005-2007, Nortel Networks
.