Ip Routing Policy - 3Com 7700 Configuration Manual

98 C 5: R
HAPTER OUTING

IP Routing Policy

P O
ROTOCOL PERATION
If the physical link and the lower layer protocol are normal, check the OSPF
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parameters configured on the interface. The parameters should be the same
parameters configured on the router adjacent to the interface. The same
area ID should be used, and the networks and the masks should also be
consistent. (The P2P or virtually linked segment can have different segments
and masks.)
Insure that the dead timer on the same interface is at least four times the
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value of the hello timer.
If the network type is NBMA, the peer must be manually specified, using the
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peer ip-address command.
If the network type is broadcast or NBMA, there must be at least one
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interface with a priority greater than zero.
If an area is set as the STUB area to which the routers are connected, the
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area on these routers must also be set as a STUB area.
The same interface type should be adopted for the neighboring routers.
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If more than two areas are configured, at least one area should be
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configured as the backbone area with an area ID of 0.
Ensure that the backbone area connects with all other areas.
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The virtual links cannot pass through the STUB area.
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Troubleshooting globally
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If OSPF cannot discover remote routes and OSPF has been configured
according to the previous procedures and you have checked all local
troubleshooting items, verify the following configurations.
If more than two areas are configured on a router, at least one area should
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be configured as the backbone area.
As shown in Figure 8, RTA and RTD are each configured to belong to only
one area, whereas RTB and RTC are both configured to belong to two
areas. RTB belongs to area0, which complies with the backbone area
membership requirement. However, RTC does not belong to area0.
Therefore, a virtual link must be set up between RTC and RTB to insure that
area2 and area0 (the backbone area) are connected.
Figure 8 OSPF Areas
area0
RTA
The backbone area (area0) cannot be configured as the STUB area and the
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virtual link cannot pass through the STUB area. So, if a virtual link has been
set up between RTB and RTC, neither area1 nor area0 can be configured as
a STUB area. Only area2 can be configured as a STUB area.
Routers in the STUB area cannot redistribute the external routes.
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When a router distributes or receives routing information, it needs to implement
some policies to filter the routing information so it can receive or distribute the
routing information that meets only the specified condition. A routing protocol
such as RIP may need to import routing information discovered by other protocols
area1
RTC
RTB
area2
RTD