HP 5500 Ei 5500 Si Switch Series Configuration Guide

 212 
Configuring the default local preference 
The local preference is used to determine the best route for traffic leaving the local AS. When a BGP 
router obtains from several IBGP peers multiple routes to the same destination but with different next hops, 
it considers the route with the highest local preference as the best route.  
This task allows you to specify the default loca l preference for routes sent to IBGP peers. 
To specify the default local preference: 
 
Step Command  Remarks 
1.  Enter...

 213 
Figure 86 Route selection based on MED  
 
 
As shown in Figure 86, Router D learns network 10.0.0.0 from  both Router A and Router B. Because 
Router B has a smaller router ID, the route learned from it is optimal.  
     Network            NextHop         MED        LocPrf     PrefVal Pa\
th/Ogn 
 *>i  10.0.0.0         2.2.2.2        50                      0       30\
0e 
 * i                   3.3.3.3        50                      0       20\
0e 
When Router D learns network 10.0.0.0 from...

 214 
Enabling the comparison of MED of routes from confederation peers 
The MED attributes of routes from confederation peers are not compared if their AS-path attributes 
contain AS numbers that do not belong to the confederation, such as these three routes: AS-path 
attributes of them are 65006 65009, 65007 65009, and 65008 65009; and MED values of them are 
2, 3, and 1. Because the third route contains an AS  number that does not belong to the confederation, 
the first route becomes the optimal...

 215 
If you have configured BGP load balancing on a BGP router, the router will set it as the next hop for routes 
s e n t  t o  a n  I B G P  p e e r  o r  p e e r  g r o u p.  T h i s  i s  d o n e  r e g a r d l e s s  o f  w h e t h e r  t h e   peer next-hop-local command 
is configured.  
To configure the next hop attribute: 
 
Step Command  Remarks 
1.  Enter system view. 
system-view N/A 
2.
  Enter BGP view. 
bgp as-number   N/A 
3.  Specify the router as the next hop of 
routes sent to a peer...

 216 
Specifying a fake AS number for a peer or peer group 
When Router A in AS 2  is moved to AS 3, you can configure Router A to specif y a fake AS number of 2  
for created connections to EBGP peers or peer groups. In this way, these EBGP peers still think Router A 
is in AS 2 and need not change their configurations. This feature ensures uninterrupted BGP services. 
To specify a fake AS number for a peer or peer group: 
 
Step Command  Remarks 
1.  Enter system view. 
system-view N/A 
2.  Enter BGP...

 217 
Removing private AS numbers from updates to a peer or peer group 
 
Step Command  Remarks 
1.  Enter system view. 
system-view N/A 
2.  Enter BGP view. 
bgp as-number   N/A 
3.  Configure BGP to remove private AS 
numbers from the AS_PATH attribute of 
updates to a peer or peer group.  peer { group-name 
| ip-address  } 
public-as-only  By default, BGP updates 
carry private AS numbers. 
 
Ignoring the first AS numb
er of EBGP route updates 
Typically, BGP checks the AS_PATH attribute of a route...

 218 
•  If the router has established a neighbor relationship with a peer, you must reset the BGP connection 
to validate the new set timers. 
•   The  timer  command takes effect for only new connections. 
•   After  peer timer  command is executed, the peer connection is closed at once, and a new 
connection to the peer is negotiated  using the configured hold time. 
To configure BGP keepalive interval and holdtime: 
 
Step Command Remarks 
1.   Enter system view. 
system-view  N/A 
2.  Enter BGP...

 219 
Configuring automatic soft-reset 
After route refresh is enabled for peers and a policy is modified, the router advertises a route-refresh 
message to the peers, which then resend their routing information to the router. After receiving the routing 
information, the router performs dynami c route update by using the new policy. 
To enable BGP route refresh for a peer or peer group: 
 
Step Command  Remarks 
1.  Enter system view. 
system-view N/A 
2.  Enter BGP view. 
bgp as-number   N/A 
3....

 220 
whether to carry non-standard ORF information in the packets). After completing the negotiation process 
and establishing the neighboring relationship, the BGP router and its BGP peer can exchange ORF 
information through specific route-refresh messages.  
For the parameters configured on both si des for ORF capability negotiation, see Tabl e  8. 
T

o enable the BGP ORF capability:  
 
Step Command Remarks 
1.   Enter system view. 
system-view  N/A 
2.  Enter BGP view. 
bgp as-number   N/A 
3....

 221 
 
Step Command  Remarks 
1.  Enter system view. 
system-view N/A 
2.  Enter BGP view. 
bgp as-number   N/A 
3.  Enable 4-byte AS 
number suppression.  peer 
{ group-name  | ip-address } 
capability-advertise suppress-4-byte-as  Disabled by default.  
 
Setting the DSCP value for BGP packets 
An IPv4 packet header contains an 8-bit Type of Servic
e (TOS) field. As defined in RFC 2474, the first six 
bits set the Differentiated Services Code Point (DSCP) value and the last two bits are reserved....