3com 3031 安装指导
466
C
HAPTER
37: IP R
OUTING
P
ROTOCOL
O
VERVIEW
Except for direct routing, IBGP and EBGP, the preferences of various dynamic
routing protocols can be manually configured to meet the user requirements. In
addition, the preferences for individual static routes can be different.
routing protocols can be manually configured to meet the user requirements. In
addition, the preferences for individual static routes can be different.
Load Balancing and
Route Backup
■
Load balancing: Support multi-route mode, permitting to configure multiple
routes that reach the same destination and use the same precedence. The
same destination can be reached via multiple different paths, whose
precedence is equal. When there is no route that can reach the same
destination with a higher precedence, the multiple routes will be adopted. The
packets are forwarded to the destination via these paths, thus implementing
load balancing.
routes that reach the same destination and use the same precedence. The
same destination can be reached via multiple different paths, whose
precedence is equal. When there is no route that can reach the same
destination with a higher precedence, the multiple routes will be adopted. The
packets are forwarded to the destination via these paths, thus implementing
load balancing.
■
Route backup: Support route backup. When main route failed, the system will
automatically switch to a backup route to improve the network reliability.In
order to achieve route backup, the user can configure multiple routes to the
same destination according to actual situation. One of the routes has the
highest precedence and is called as main route. The other routes have
descending precedence and are called as backup routes. Normally, the router
sends data via main route. When the line is in failure, the main route will hide
itself and the router will choose one route whose precedence is higher than
others from the left routes as a path to send data. In this way, the switchover
from the main route to the backup route is realized. When the main route
recovers, the router will restore it and re-select route. As the main route has
the highest precedence, the router will choose the main route to send data.
This process is the automatic switchover from the backup route to the main
route.
automatically switch to a backup route to improve the network reliability.In
order to achieve route backup, the user can configure multiple routes to the
same destination according to actual situation. One of the routes has the
highest precedence and is called as main route. The other routes have
descending precedence and are called as backup routes. Normally, the router
sends data via main route. When the line is in failure, the main route will hide
itself and the router will choose one route whose precedence is higher than
others from the left routes as a path to send data. In this way, the switchover
from the main route to the backup route is realized. When the main route
recovers, the router will restore it and re-select route. As the main route has
the highest precedence, the router will choose the main route to send data.
This process is the automatic switchover from the backup route to the main
route.
For the same destination, a specified routing protocol may find multiple different
routes. If the routing protocol has the highest precedence among all active routing
protocols, these multiple routes will be regarded as currently valid routes. Thus,
load balancing of IP traffic is ensured in terms of routing protocols. By far, the
routing protocols that support load balancing include OSPF, BGP and IS-IS. Static
route also supports load balancing.
routes. If the routing protocol has the highest precedence among all active routing
protocols, these multiple routes will be regarded as currently valid routes. Thus,
load balancing of IP traffic is ensured in terms of routing protocols. By far, the
routing protocols that support load balancing include OSPF, BGP and IS-IS. Static
route also supports load balancing.
Routes Shared between
Routing Protocols
As the algorithms of various routing protocols are different, different routing
protocols may learn different routes, which leads to the problem of how to share
the learned routes between the routing protocols. A router can import the route
protocols may learn different routes, which leads to the problem of how to share
the learned routes between the routing protocols. A router can import the route
Table 537 Routing protocols and route discovery preferences
Routing Protocol or Route Type
The Preference of the Corresponding Route
DIRECT
0
OSPF
10
IS-IS
15
STATIC
60
RIP
100
OSPF ASE
150
OSPF NSSA
150
IBGP
256
EBGP
256
UNKNOWN
255