7.5 Using Multiple Routing Protocols
7.5.4 Redistribution guidelines
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.