Examples about how
redistribution can be implemented are covered later in this chapter.
At a high level, Cisco recommends that you consider employing the
following guidelines when using redistribution:
- Be familiar with
your network
--- This
is the overriding recommendation. There are many ways to implement
redistribution, so knowing your network will enable you to make
the best decision. Use an analyzer to track your data flows.
Do not overlap
routing protocols
--- Do
not run two different protocols in the same internetwork. Rather,
have distinct boundaries between networks that use different
protocols.
One-way
redistribution
--- To
avoid routing loops and having problems with varying convergence
time, allow routes to be exchanged in only one direction, not both
directions. In the other direction, you should consider using a
default route. This is important for cases when you have multiple
points of redistribution. If you have only one ASBR, full two-way
redistribution is recommended.
Two-way
redistribution
--- In
case of only one point of redistribution (one ASBR only), there are
no potential problems. If you have multiple ASBRs and if you must
allow two-way redistribution, enable a mechanism to reduce the
chances of routing loops. Examples of mechanisms already covered in
this chapter are default routes, route filters, and modification of
the metrics advertised. With these types of mechanisms, you can
reduce the chances of routes imported from one AS being reinjected
into the same AS as new route information.
Use the following redistribute?
command to see a list of protocols that can be supported by
redistribution:
p1r1(config-router)#redistribute?
Bgp Border Gateway
Protocol (BGP)
connected Connected
egp Exterior Gateway
Protocol (EGP)
eigrp Enhanced
Interior Gateway Routing Protocol (EIGRP)
igrp Interior Gateway
Routing Protocol (IGRP)
isis ISO IS-IS
iso-igrp IGRP for OSI
networks
mobile Mobile routes
odr On Demand Stub
Routes
ospf Open Shortest
Path First (OSPF)
rip Routing
Information Protocol (RIP)
static Static routes
As shown previously
for IP, all protocols are supported by redistribution. Before
implementing redistribution, consider the following points:
- You can
redistribute only protocols that support the same protocol
stack. For example, you can redistribute between IP RIP and OSPF
because they both support the TCP/IP stack, but you cannot
redistribute between Internetwork Packet Exchange (IPX) RIP and
OSPF because IPX RIP supports the IPX/Sequenced Packet Exchange
(SPX) stack and OSPF does not.
- How you configure
redistribution varies among protocols and among combinations of
protocols. For example, redistribution occurs automatically
between IGRP and EIGRP when they have the same AS number, but it
must be configured between EIGRP and RIP.
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