Riverbed SteelHead 3070-SD, Руководство пользователя

Страница: 44 / 124

44 | Configuring BGP, OSPF, Static Routing, and Route Retraction on SteelHead SD
Configuring BGP on SteelHead SD
The hold-time value is three times the interval at which keepalive messages are sent. Using the
default values for the keepalive time of 60 and the hold time of 180, the settings work together
like this: after two neighbors establish an eBGP session, 60 seconds later they’ll each send a
keepalive message. When a gateway receives a keepalive message from its neighbor, that
gateway’s hold time for the session will have counted down from 180 to 120, but it’s then reset
to 180. This process continues every 60 seconds. However, should neighbor A lose power, then
neighbor B won’t receive any keepalives. So after 180 seconds, neighbor B determines that
neighbor A is down and closes the session.
– Weight - Specify the BGP weight value to the routes received from the BGP neighbor. A route
with a high weight value is preferred among multiple routes with the same destination. The
default value is range is 2 to 65534. For details on how the weight metric is used in BGP path
selection, see
“Configuring BGP path selection” on page 45 .
– Next hop self - Click On to change the next hop attribute for received updates to its own IP
address. Enable this option to change the next-hop attribute for external networks that will be
advertised to branch route.
When routes from another AS are learned via the eBGP neighbor, the next hop for that route
isn’t changed when it is passed to its iBGP peers. As an iBGP peer may not be aware of next hop
of the external route, that route becomes unreachable for the iBGP peer. If the iBGP neighbor is
configured with the Next-hop self option, the next hop is changed to its own interface address
which is reachable from the iBGP neighbor.
– Default route originate - Click On to distribute the default route (0.0.0.0/0) to the specified BGP
neighbor. The default setting is Off .
Route map - Click the search selector and select the route use case. The routing policies
defined by the selected route map are applied while accepting routes to the BGP neighbor.
10. Click Submit .
11. Repeat Step 5 through Step 10 if you have two MPLS providers that need to do BGP peering with the
current appliance. You need to create a BGP configuration for each one.
12. Repeat this process for other SteelHead SDs behind other routers.
Note: BGP redistribution and summarization can only be configured after you have defined route maps and prefixes.
Configuring BGP routing policies
Optionally, you can configure BGP routing polices by defining inbound and outbound prefixes, AS paths,
and route maps for BGP neighbors. By specifying these options, you can define what inbound and
outbound routes are allowed or denied for BGP neighbors.
We recommend you define route maps, AS lists, and prefix lists before you configure the inbound and
outbound settings. For details on configuring routing policies, see
“Overview of routing policies on
SteelHead SD” on page 69 .