H3C Technologies H3C S5560 Series Switches - Manual (Page 95)

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• Type-5 LSAs.
• Type-7 LSAs in an NSSA area.
• Type-5 LSAs translated by the ASBR (also an ABR) from Type-7 LSAs in an NSSA area.
If the ASBR (ABR) is not a translator, it cannot summarize routes in Type-5 LSAs translated from
Type-7 LSAs.
To configure route summarization on an ASBR:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter OSPF view.
ospf [ process-id | router-id router-id
| vpn-instance vpn-instance-name ]* N/A
3. Configure ASBR route
summarization.
asbr-summary ip-address
{ mask-length | mask } [ cost cost |
not-advertise | nssa-only | tag tag ] *
By default, route summarization is not
configured on an ASBR.
Configuring discard routes for summary networks
Discard routes help prevent routing black holes when route summarization is configured on ABRs and
ASBRs.
During route summarization, an ABR or ASBR generates a discard route for the summary network. The
destination and output interface of the discard route is the summary network and interface Null 0. When
receiving packets destined for a nonexistent network that is a part of the summary network, the ABR or
ASBR discards the packets according to the discard route.
For example, Router A summarizes networks 19.1.1.0/24, 19.1.2.0/24, and 19.1.3.0/24 into network
19.1.0.0/16, and advertises the summary network to Router B. When Router B receives a packet destined
for 19.1.4.0/24, Router B forwards the packet to Router A according to the summary route. Because no
specific route to 19.1.4.0/24 exists, Router A discards the packet according to the discard route.
To configure discard routes for summary networks:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter OSPF view.
ospf [ process-id | router-id router-id
| vpn-instance vpn-instance-name ] * N/A
3. Configure discard routes
for summary networks.
discard-route { external
{ external-preference | suppression }
| internal { internal-preference |
suppression } } *
By default:
• The ABR or ASBR generates
discard routes for summary
networks.
• The preference of discard
routes is 255.
Configuring received OSPF route filtering
Perform this task to filter routes calculated using received LSAs.
The following filtering methods are available:
• Use an ACL or IP prefix list to filter routing information by destination address.