Riverbed SteelHead 3070-SD, Руководство пользователя

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Configuring BGP, OSPF, Static Routing, and Route Retraction on SteelHead SD | 51
Configuring BGP on SteelHead SD
7. Select the origin type from the list:
• igp - Set the prefix to originate from routing information learned from the interior gateway protocol
(IGP) such as OSPF.
• egp -Network layer reachability information (NLRI) is learned via EGP, as indicated by “e” in the BGP
table.
• incomplete - Set the prefix to originate from an aggregate statement or via redistribution of a static
route.
8. Specify the remaining match criteria. For details, see “Configuring route maps” on page 76 .
9. Click Submit .
Enabling multi exit discriminator (MED) settings
In BGP path selection, you configure MED attributes when there are multiple paths to a destination prefix
that have the same local preference and the same AS path length. The purpose of the MED settings is to
select the best path when there are multiple connections between two autonomous systems.
The MED attribute is applied to outbound routes, dictating the best inbound path into the AS (assuming
multiple paths exist). When a BGP speaker learns a route from a peer, it can pass the route's MED to any
iBGP peers, but not to eBGP peers. As a result, the MED has relevance only between neighboring
autonomous systems.
MED is a BGP path attribute that can influence the route selection process. MED breaks the tie between
the two routes when the weight, local preference, AS-Path, and origin type are same. For details, see
“Configuring BGP path selection” on page 45 .
You can configure these MED types:
• Deterministic MED - Enabling this option ensures the comparison of the MED variable when
choosing routes advertised by different peers in the same autonomous system.
• Always-compare MED - Enabling this option ensures the comparison of the MED for paths from
neighbors in different autonomous systems.
To enable multi-exit discriminator settings
1. Choose Appliances and select the appliance to expand the pane.