Tänkte roa mig med att göra lite OSPF-labbar från GNS3 Vault, först ut var denna om Summarization Discard Route. 
Goal:
- All IP addresses have been preconfigured for you.
- Configure OSPF and use the correct areas.
- Configure a loopback0 interface on router Spielburg with network address 3.3.3.3 /24.
- Configure router Shapeir to summarize network 3.3.3.0 /24 to 3.0.0.0 /8.
- Configure router Shapeir so it doesn’t add a null0 entry in its routing table.
Konfig:
Basic config på samtliga enheter, summera nät kan vi som bekant endast göra på ABR. För interna nät används area x range, E1/E2 använder summary-address direkt på ASBR.
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Tarna
router ospf 1
log-adjacency-changes
network 192.168.12.0 0.0.0.255 area 0
Shapeir
router ospf 1
log-adjacency-changes
area 1 range 3.0.0.0 255.0.0.0
network 192.168.12.0 0.0.0.255 area 0
network 192.168.23.0 0.0.0.255 area 1
Spielburg
interface Loopback0
ip address 3.3.3.3 255.255.255.0
router ospf 1
log-adjacency-changes
network 3.3.3.0 0.0.0.255 area 1
network 192.168.23.0 0.0.0.255 area 1
Vilket ger följande resultat i Tarna:
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Tarna#sh ip route | beg Gate
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet0/0
O IA 3.0.0.0/8 \[110/3\] via 192.168.12.2, 00:24:49, FastEthernet0/0
O IA 192.168.23.0/24 \[110/2\] via 192.168.12.2, 00:32:18, FastEthernet0/0
Och i Shapeir:
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Shapeir#sh ip route | beg Gate
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet1/0
3.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 3.3.3.3/32 \[110/2\] via 192.168.23.3, 00:00:23, FastEthernet0/0
**O 3.0.0.0/8 is a summary, 00:00:23, Null0**
C 192.168.23.0/24 is directly connected, FastEthernet0/0
Det var null0-routen vi ej fick ha.. Här körde jag fast rätt rejält, en lösning hade ju kunnat vara att göra en statisk route på Speilberg och sedan redistributa in den i OSPF, men enligt labben skulle konfigändringen göras i Shapeir.. Titeln på labben spoilade dock lite, följande information fanns att läsa på Cisco’s OSPF Commands:
discard-route
| To reinstall either an external or internal discard route that was previously removed, use the discard-route command in router configuration mode. To remove either an external or internal discard route, use the no form of this command. discard-route [external | internal] no discard-route [external | internal] |
Syntax Description
external
(Optional) Reinstalls the discard route entry for redistributed summarized routes on an Autonomous System Boundary Router (ASBR).
internal
(Optional) Reinstalls the discard-route entry for summarized internal routes on the Area Border Router (ABR).
Hemligheten ligger i “To remove either an external or internal discard route, use the no form of this command.” Testade helt enkelt med “no discard-route internal” och vips så var null0-routen borta. :)
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router ospf 1
no discard-route internal
Shapeir#sh ip route | beg Gate
Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, FastEthernet1/0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 \[110/2\] via 192.168.23.3, 00:18:12, FastEthernet0/0
C 192.168.23.0/24 is directly connected, FastEthernet0/0
Vet inte om jag ser så mycket praktiskt nytta att använda detta dock. :P