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ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Poison Reverse

Poison Reverse

Poison reverse allows a RIP-enabled interface to set the cost of the route that it learns from a neighbor to 16 (indicating that the route is unreachable) and then send the route back. After receiving this route, the neighbor deletes the useless route from its routing table, which prevents loops.

Figure 4-5 Networking for poison reverse

In Figure 4-5, Device A sends Device B a route to 10.0.0.0/8. If poison reverse is not configured, Device B will send this route back to Device A after learning it from Device A. As a result, Device A learns the following routes to 10.0.0.0/8:
  • A direct route with zero hops
  • A route with Device B as the next hop and total two hops
Only direct routes, however, are active in the RIP routing table of Device A.

If the route from Device A to 10.0.0.0 becomes unreachable and Device B is not notified, Device B still considers the route to 10.0.0.0/8 reachable and continues sending this route to Device A. Then, Device A receives incorrect routing information and considers the route to 10.0.0.0/8 reachable through Device B; Device B considers the route to 10.0.0.0/8 reachable through Device A. As a result, a loop occurs on the network.

With poison reverse, after Device B receives the route from Device A, Device B sends a route unreachable message to Device A with cost 16. Device A then no longer learns the reachable route from Device B, which prevents routing loops.

If both split horizon and poison reverse are configured, only poison reverse takes effect.

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Updated: 2019-01-04

Document ID: EDOC1100059473

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